🏗️Software Engineering: Software Maintenance (Just the Quotes)

"A clean design is more easily modified as requirements change or as more is learned about what parts of the code consume significant amounts of execution time. A 'clever' design that fails to work or to run fast enough can often be salvaged only at great cost. Efficiency does not have to be sacrificed in the interest of writing readable code - rather, writing readable code is often the only way to ensure efficient programs that are also easy to maintain and modify." (Brian W Kernighan & Phillip J Plauger, "The Elements of Programming Style", 1974)

"Most programs are too big to be comprehended as a single chunk. They must be divided into smaller pieces that can be conquered separately. That is the only way to write them reliably; it is the only way to read and understand them. [...] When a program is not broken up into small enough pieces, the larger modules often fail to deliver on these promises. They try to do too much, or too many different things, and hence are difficult to maintain and are too specialized for general use." (Brian W Kernighan & Phillip J Plauger, "The Elements of Programming Style", 1974)

"Programs are not used once and discarded, nor are they run forever without change. They evolve. The new version of the integration program has a greater likelihood of surviving changes later without acquiring bugs. It assists instead of intimidating those who must maintain it." (Brian W Kernighan & Phillip J Plauger, "The Elements of Programming Style", 1974)

"All repairs tend to destroy the structure, to increase the entropy and disorder of the system. Less and less effort is spent on fixing the original design flaws; more and more is spent on fixing flaws introduced by earlier fixes. As time passes, the system becomes less and less well-ordered. Sooner or later the fixing ceases to gain any ground. Each forward step is matched by a backward one. Although in principle usable forever, the system has worn out as a base for progress." (Frederick P. Brooks, "The Mythical Man-Month", 1975)

"Clearly, methods of designing programs so as to eliminate or at least illuminate side effects can have an immense payoff in maintenance costs. So can methods of implementing designs with fewer people, fewer interfaces, and hence fewer bugs." (Fred P Brooks, "The Mythical Man-Month: Essays", 1975)

"Program maintenance involves no cleaning, lubrication, or repair of deterioration. It consists chiefly of changes that repair design defects. Much more often than with hardware, these changes include added functions. Usually they are visible to the user." (Fred P Brooks, "The Mythical Man-Month: Essays", 1975)

"Systems program building is an entropy-decreasing process, hence inherently metastable. Program maintenance is an entropy-increasing process, and even its most skillful execution only delays the subsidence of the system into unfixable obsolescence." (Fred P Brooks, "The Mythical Man-Month: Essays", 1975)

"The fundamental problem with program maintenance is that fixing a defect has a substantial (20-50 percent) chance of introducing another. So the whole process is two steps forward and one step back." (Fred P Brooks, "The Mythical Man-Month: Essays", 1975)

"The fundamental problem with software maintenance is that fixing a defect has a substantial (20-50 percent) chance of introducing another. So the whole process is two steps forward and one step back. Why aren't defects fixed more cleanly? First, even a subtle defect shows itself as a local failure of some kind. In fact it often has system-wide ramifications, usually nonobvious. Any attempt to fix it with minimum effort will repair the local and obvious, but unless the structure is pure or the documentation very fine, the far-reaching effects of the repair will be overlooked. Second, the repairer is usually not the man who wrote the code, and often he is a junior programmer or trainee. (Frederick P. Brooks, "The Mythical Man-Month" , 1975)

"[Enterprise Architecture is] the set of descriptive representations (i. e., models) that are relevant for describing an Enterprise such that it can be produced to management's requirements (quality) and maintained over the period of its useful life." (John Zachman, 1987)

"The most common kind of coding bug, and often considered the least harmful, are documentation bugs (i.e., erroneous comments). Although many documentation bugs are simple spelling errors or the result of poor writing, many are actual errors - that is, misleading or erroneous comments. We can no longer afford to discount such bugs, because their consequences are as great as 'true' coding errors. Today programming labor is dominated by maintenance. This will increase as software becomes even longer-lived. Documentation bugs lead to incorrect maintenance actions and therefore cause the insertion of other bugs." (Boris Beizer, "Software Testing Techniques", 1990)

"The majority of the cost of a software project is in long-term maintenance. In order to minimize the potential for defects as we introduce change, it’s critical for us to be able to understand what a system does. As systems become more complex, they take more and more time for a developer to understand, and there is an ever greater opportunity for a misunderstanding. Therefore, code should clearly express the intent of its author. The clearer the author can make the code, the less time others will have to spend understanding it. This will reduce defects and shrink the cost of maintenance." (Robert C Martin, "Clean Code: A Handbook of Agile Software Craftsmanship", 2008)

"Architecture is the set of descriptive representations that are required in order to create an object. If you can’t describe it, you can’t create it. Also, if you ever want to change the object you created, Architecture constitutes the baseline for changing the object once it is created; that is, it is the baseline for changing the object IF you retain the descriptive representations used in its creation and IF you ensure that the descriptive representations are always maintained consistent with the instantiation." (John Zachman, "Architecture Is Architecture Is Architecture", [Ed. Leon A Kappelman, "The Sim Guide To Enterprise Architecture"] 2009)

"Writing and (particularly) maintaining software is a continual battle against entropy. Keeping on top of quality is tough, requiring high levels of discipline. This discipline is difficult enough to maintain under the best of circumstances, let alone when faced with concrete evidence that the software is uncared for, such as a long-unfixed bug. As soon as discipline slips, quality can go into a self-reinforcing downward spiral, and you’re in real trouble." (Paul Butcher, "Debug It! Find, Repair, and Prevent Bugs in Your Code", 2009)

"Few would deny the importance of writing quality code. High quality code contains less bugs, and is easier to understand and easier to maintain. However, the precise definitions of code quality can be more subjective, varying between organizations, teams, and even individuals within a team." (John F Smart, "Jenkins: The Definitive Guide", 2011)

"A lack of focus on a shared language and knowledge of the problem domain results in a codebase that works but does not reveal the intent of the business. This makes codebases difficult to read and maintain because translations between the analysis model and the code model can be costly and error prone." (Scott Millett, "Patterns Principles and Practices of Domain Driven Design", 2015)

"The fact that software engineering is not like other forms of engineering should really come as no surprise. Medicine is not like the law. Carpentry is not like baking. Software development is like one thing, and one thing only: software development. We need practices that make what we do more efficient, more verifiable, and easier to change. If we can do this, we can slash the short-term cost of building software, and all but eliminate the crippling long-term cost of maintaining it." (David S Bernstein, "Beyond Legacy Code", 2015)

"There is common but flawed notion in enterprise IT circles that maintenance work requires less skill than full-scale development. As a result, project sponsors looking to reduce cost opt for a different team of lower-cost people for maintenance work. This is false economy. It hurts the larger business outcome and reduces IT agility." (Sriram Narayan, "Agile IT Organization Design: For Digital Transformation and Continuous Delivery", 2015)

"The goal of software architecture is to minimize the human resources required to build and maintain the required system." (Robert C Martin, "Clean Architecture: A Craftsman's Guide to Software Structure and Design", 2017)

"When software is done right, it requires a fraction of the human resources to create and maintain. Changes are simple and rapid. Defects are few and far between. Effort is minimized, and functionality and flexibility are maximized." (Robert C Martin, "Clean Architecture: A Craftsman's Guide to Software Structure and Design", 2017)

🏗️Software Engineering: Perfection (Just the Quotes)

"[...] no program is ever perfect; there is always room for improvement. Of course, it is foolish to polish a program beyond the point of diminishing returns, but most programmers do too little revision; they are satisfied too early. Don't stop with your first draft." (Brian W Kernighan & Phillip J Plauger, "The Elements of Programming Style", 1974)

"Software never was perfect and won't get perfect. But is that a license to create garbage? The missing ingredient is our reluctance to quantify quality." (Boris Beizer, "Software Testing Techniques", 1990)

"Do build perfectly for today. Do the simple thing that solves today's problem, but do it well. Keep the code of high quality, just perfect for today's needs." (Ron Jeffries, "Extreme Programming Installed", 2001)

"Users may be annoyed by bugs, and software developers may be disappointed by their inability to perfect their work, and managers may be frustrated by the unreliability of their plans. But in the end, none of that matters as much as the simple fact that software does not work the way we think, and until it does, it is not worth trying to perfect." (Scott Rosenberg, "Dreaming in Code", 2007)

"Prototyping is always inspirational - not in the sense of a perfected artwork but just the opposite: because it inspires new ideas. Prototyping should start early in the life of a project, and we expect them to be numerous, quickly executed, and pretty ugly." (Tim Brown, "Change by Design: How Design Thinking Transforms Organizations and Inspires Innovation", 2009)

"The fact that bugs will certainly occur in your code does not mean you aren’t responsible for them. The fact that the task to write perfect software is virtually impossible does not mean you aren’t responsible for the imperfection." (Robert C Martin,"The Clean Coder: A code of conduct for professional programmers", 2011)

"Areas of low complexity or that are unlikely to be invested in can be built without the need for perfect code quality; working software is good enough. Sometimes feedback and first-to-market are core to the success of a product; in this instance, it can make business sense to get working software up as soon as possible, whatever the architecture." (Scott Millett, "Patterns Principles and Practices of Domain Driven Design", 2015)

"Not all of a large software product needs be perfectly designed - in fact trying to do so would be a waste of effort." (Scott Millett, "Patterns Principles and Practices of Domain Driven Design", 2015)

"People are inherently imperfect - we like to say that humans are mostly a collection of intermittent bugs. But before you can understand the bugs in your coworkers, you need to understand the bugs in yourself. We’re going to ask you to think about your own reactions, behaviors, and attitudes - and in return, we hope you gain some real insight into how to become a more efficient and successful software engineer who spends less energy dealing with people-related problems and more time writing great code." (Titus Winters, "Software Engineering at Google: Lessons Learned from Programming Over Time", 2020)

🏗️Software Engineering: Heuristic (Just the Quotes)

"Heuristic reasoning is reasoning not regarded as final and strict but as provisional and plausible only, whose purpose is to discover the solution of the present problem. We are often obliged to use heuristic reasoning. We shall attain complete certainty when we shall have obtained the complete solution, but before obtaining certainty we must often be satisfied with a more or less plausible guess. We may need the provisional before we attain the final. We need heuristic reasoning when we construct a strict proof as we need scaffolding when we erect a building." (George Pólya, "How to Solve It", 1945)

"The aim of heuristics is to study the methods and rules of discovery and invention. [...] Heuristic, as an adjective, means 'serving to discover'." (George Pólya, "How to Solve It", 1945)

"An algorithm gives you the instructions directly. A heuristic tells you how to discover the instructions for yourself, or at least where to look for them." (Steve McConnell, "Code Complete", 1993)

"Heuristic (it is of Greek origin) means discovery. Heuristic methods are based on experience, rational ideas, and rules of thumb. Heuristics are based more on common sense than on mathematics. Heuristics are useful, for example, when the optimal solution needs an exhaustive search that is not realistic in terms of time. In principle, a heuristic does not guarantee the best solution, but a heuristic solution can provide a tremendous shortcut in cost and time." (Nikola K Kasabov, "Foundations of Neural Networks, Fuzzy Systems, and Knowledge Engineering", 1996)

"Heuristic methods may aim at local optimization rather than at global optimization, that is, the algorithm optimizes the solution stepwise, finding the best solution at each small step of the solution process and 'hoping' that the global solution, which comprises the local ones, would be satisfactory." (Nikola K Kasabov, "Foundations of Neural Networks, Fuzzy Systems, and Knowledge Engineering", 1996)

"Models of bounded rationality describe how a judgement or decision is reached (that is, the heuristic processes or proximal mechanisms) rather than merely the outcome of the decision, and they describe the class of environments in which these heuristics will succeed or fail." (Gerd Gigerenzer & Reinhard Selten [Eds., "Bounded Rationality: The Adaptive Toolbox", 2001)

"A heuristic is a rule applied to an existing solution represented in a perspective that generates a new (and hopefully better) solution or a new set of possible solutions." (Scott E Page, "The Difference: How the Power of Diversity Creates Better Groups, Firms, Schools and Societies", 2008)

"There are two parts to learning craftsmanship: knowledge and work. You must gain the knowledge of principles, patterns, practices, and heuristics that a craftsman knows, and you must also grind that knowledge into your fingers, eyes, and gut by working hard and practicing." (Robert C Martin, "Clean Code: A Handbook of Agile Software Craftsmanship", 2008)

"A second class of metaphors - mathematical algorithms, heuristics, and models - brings us closer to the world of computer science programs, simulations, and approximations of the brain and its cognitive processes." (Diego Rasskin-Gutman, "Chess Metaphors: Artificial Intelligence and the Human Mind", 2009)

"[...] heuristics are simple, efficient rules - either hard-wired in our brains or learned - that kick in especially when we're facing problems with incomplete information." (David DiSalvo, "What Makes Your Brain Happy and Why You Should Do the Opposite", 2011)

"This is the essence of intuitive heuristics: when faced with a difficult question, we often answer an easier one instead, usually without noticing the substitution." (Daniel Kahneman, "Thinking, Fast and Slow", 2011)

"Heuristics are simplified rules of thumb that make things simple and easy to implement. But their main advantage is that the user knows that they are not perfect, just expedient, and is therefore less fooled by their powers. They become dangerous when we forget that." (Nassim N Taleb, "Antifragile: Things that gain from disorder", 2012)

"A good heuristic decision is made by 1) knowing what to look for, 2) knowing when enough information is enough (the 'threshold of decision' ), and 3) knowing what decision to make." (Patrick Van Horne, "Left of Bang", 2014)

"Heuristic decision making is fast and frugal and is often based on the evaluation of one or two salient bits of information." (Amitav Chakravarti, "Why People (Don’t) Buy: The Go and Stop Signals", 2015)

"A heuristic is a strategy we derive from previous experience with a similar problem." (Darius Foroux, "Think Straight", 2017)

More quotes on "Heuristic" at the-web-of-knowledge.blogspot.com. 

🏗️Software Engineering: Bugs (Just the Quotes)

"Program testing can be used to show the presence of bugs, but never to show their absence!" (Edsger W Dijkstra, "Notes On Structured Programming", 1970)

"If you want more effective programmers, you will discover that they should not waste their time debugging, they should not introduce the bugs to start with." (Edsger W Dijkstra, "The Humble Programmer", 1972)

"In the good old days physicists repeated each other's experiments, just to be sure. Today they stick to FORTRAN, so that they can share each other's programs, bugs included." (Edsger W Dijkstra, "How do we tell truths that might hurt?", 1975)

"The fundamental problem with software maintenance is that fixing a defect has a substantial (20-50 percent) chance of introducing another. So the whole process is two steps forward and one step back. Why aren't defects fixed more cleanly? First, even a subtle defect shows itself as a local failure of some kind. In fact it often has system-wide ramifications, usually nonobvious. Any attempt to fix it with minimum effort will repair the local and obvious, but unless the structure is pure or the documentation very fine, the far-reaching effects of the repair will be overlooked. Second, the repairer is usually not the man who wrote the code, and often he is a junior programmer or trainee. (Frederick P. Brooks, "The Mythical Man-Month" , 1975)

"Each new user of a new system uncovers a new class of bugs." (Brian W Kernighan, "Programming Pearls", 1985)

"Code migrates to data. Because of this law there is increasing awareness that bugs in code are only half the battle and that data problems should be given equal attention."  (Boris Beizer, "Software Testing Techniques", 1990)

"Failure to initialize a shared object can lead to data-dependent bugs caused by residues from a previous use of that object by another transaction. Note that the culprit transaction is long gone when the bug's symptoms are discovered. Because the effect of corruption of dynamic data can be arbitrarily far removed from the cause, such bugs are among the most difficult to catch." (Boris Beizer, "Software Testing Techniques", 1990)

"The complexity barrier. Software complexity (and therefore that of bugs) grows to the limits of our ability to manage that complexity." (Boris Beizer, "Software Testing Techniques", 1990)

"The most common kind of coding bug, and often considered the least harmful, are documentation bugs (i.e., erroneous comments). Although many documentation bugs are simple spelling errors or the result of poor writing, many are actual errors - that is, misleading or erroneous comments. We can no longer afford to discount such bugs, because their consequences are as great as 'true' coding errors. Today programming labor is dominated by maintenance. This will increase as software becomes even longer-lived. Documentation bugs lead to incorrect maintenance actions and therefore cause the insertion of other bugs." (Boris Beizer, "Software Testing Techniques", 1990)

"The pesticide paradox. Every method you use to prevent or find bugs leaves a residue of subtler bugs against which those methods are ineffective."  (Boris Beizer, "Software Testing Techniques", 1990)

"Design bugs are often subtle and occur by evolution with early assumptions being forgotten as new features or uses are added to systems." (Fernando J Corbató, "On Building Systems That Will Fail", 1991)

"The real value of tests is not that they detect bugs in the code, but that they detect inadequacies in the methods, concentration, and skills of those who design and produce the code." (Charles A R Hoare, "How Did Software Get So Reliable Without Proof?", Lecture Notes in Computer Science Vol. 1051, 1996)

"Beauty is more important in computing than anywhere else in technology because software is so complicated. Beauty is the ultimate defense against complexity." (David Gelernter, "Machine Beauty: Elegance And The Heart Of Technolog", 1998)

"Bug tracking will allow you to uncover 'smells' in code (to use a refactoring phrase). If there are a large number of problems in a particular segment of your project then you may want to really focus on that segment and stabilize it. How do you identify this clustering unless you keep track of the errors."(Ken Beck, 1999)

"Bugs are things that creep into your software against your will. Every defect in your code was put there by one of the programmers. Two of the programmers, with pair programming. With the customers we visit, when something goes wrong, they think it's a defect." (Ron Jeffries, "Extreme Programming Installed", 2001)

"The longer we wait between integrations and acceptance tests, the worse things get. Wait twice as long and we'll have four or more times the hassle. The reason is that one bug written just yesterday is pretty easy to find, while ten or a hundred written weeks ago can become almost impossible." (Ron Jeffries, "Extreme Programming Installed", 2001)

"Unit tests can be tedious to write, but they save you time in the future (by catching bugs after changes). Less obviously, but just as important, is that they can save you time now: tests focus your design and implementation on simplicity, they support refactoring, and they validate features as you develop." (Ron Jeffries, "Extreme Programming Installed, 2001)

"People also underestimate the time they spend debugging. They underestimate how much time they can spend chasing a long bug. With testing, I know straight away when I added a bug. That lets me fix the bug immediately, before it can crawl off and hide. There are few things more frustrating or time wasting than debugging. Wouldn't it be a hell of a lot quicker if we just didn't create the bugs in the first place?" (Martin Fowler, 2002)

"Refactoring is risky. It requires changes to working code that can introduce subtle bugs. Refactoring, if not done properly, can set you back days, even weeks. And refactoring becomes riskier when practiced informally or ad hoc." (Erich Gamma, 2002)

"Refactoring is the process of changing a software system in such a way that it does not alter the external behavior of the code yet improves its internal structure. It is a disciplined way to clean up code that minimizes the chances of introducing bugs. In essence when you refactor you are improving the design of the code after it has been written." (Martin Fowler et al, "Refactoring: Improving the Design of Existing Code", 2002)

"Refactoring changes the programs in small steps. If you make a mistake, it is easy to find the bug." (Martin Fowler et al, "Refactoring: Improving the Design of Existing Code", 2002)

"All OO languages show some tendency to suck programmers into the trap of excessive layering. Object frameworks and object browsers are not a substitute for good design or documentation, but they often get treated as one. Too many layers destroy transparency: It becomes too difficult to see down through them and mentally model what the code is actually doing. The Rules of Simplicity, Clarity, and Transparency get violated wholesale, and the result is code full of obscure bugs and continuing maintenance problems." (Eric S. Raymond, "The Art of Unix Programming", 2003)

"Old code rarely offers trendy graphics or flavor-of-the-month features, but it has one considerable ad - vantage: It tends to work. A program that has been well used is like an old garden that has been well tended or a vintage guitar that has been well played: Its rough edges have been filed away, its bugs have been found and fixed, and its performance is a known and valuable quantity." (Scott Rosenberg, "Dreaming in Code", 2007)

"Users may be annoyed by bugs, and software developers may be disappointed by their inability to perfect their work, and managers may be frustrated by the unreliability of their plans. But in the end, none of that matters as much as the simple fact that software does not work the way we think, and until it does, it is not worth trying to perfect." (Scott Rosenberg, "Dreaming in Code", 2007)

"Well-commented code is one hallmark of good programming practice; it shows that you care about what you’re doing, and it is considerate to those who will come after you to fix your bugs. But comments also serve as a kind of back channel for programmer-to-programmer communication and even occasionally as a competitive arena or an outlet for silliness." (Scott Rosenberg, "Dreaming in Code", 2007)

"It is unit tests that keep our code flexible, maintainable, and reusable. The reason is simple. If you have tests, you do not fear making changes to the code! Without tests every change is a possible bug."  (Robert C Martin, "Clean Code: A Handbook of Agile Software Craftsmanship", 2008)

"But remember that refactoring should never be combined with modifying the functionality of the code, and that very definitely includes fixing bugs." (Paul Butcher, "Debug It! Find, Repair, and Prevent Bugs in Your Code", 2009)

"Crying that it's an application bug is like crying over the speed of light: you should deal with reality, not what you wish reality was." (Linus Torvalds, 2009)

"Every piece of code is built upon a platform of myriad assumptions - things that have to be true for it to behave as expected. More often than not, bugs arise because one or more of these assumptions are violated or turn out to be mistaken." (Paul Butcher, "Debug It! Find, Repair, and Prevent Bugs in Your Code", 2009)

"Most bugs are caused by simple oversights. Yes, occasionally you will be faced by something very subtle, but don’t overlook the simple things." (Paul Butcher, "Debug It! Find, Repair, and Prevent Bugs in Your Code", 2009)

"One final point - whether fixing bugs or implementing new functionality, it’s good practice to always examine exactly what it is that you’re about to check in before every check-in. It won’t take long, and every once in a while, you’ll catch a change that you really didn’t intend to make from slipping through."  (Paul Butcher, "Debug It! Find, Repair, and Prevent Bugs in Your Code", 2009)

"Successful reproduction [of bugs] is all about control. If you control all the relevant variables, you will reproduce your problem. The trick, of course, is identifying which variables are relevant to the bug at hand, discovering what you need to set them to, and finding a way to do so." (Paul Butcher, "Debug It! Find, Repair, and Prevent Bugs in Your Code", 2009)

"In many applications, integration or functional tests are used by default as the standard way to test almost all aspects of the system. However integration and functional tests are not the best way to detect and identify bugs. Because of the large number of components involved in a typical end-to-end test, it can be very hard to know where something has gone wrong. In addition, with so many moving parts, it is extremely difficult, if not completely unfeasible, to cover all of the possible paths through the application." (John F Smart, "Jenkins: The Definitive Guide", 2011)

"Few would deny the importance of writing quality code. High quality code contains less bugs, and is easier to understand and easier to maintain. However, the precise definitions of code quality can be more subjective, varying between organizations, teams, and even individuals within a team." (John F Smart, "Jenkins: The Definitive Guide", 2011)

"The fact that bugs will certainly occur in your code does not mean you aren’t responsible for them. The fact that the task to write perfect software is virtually impossible does not mean you aren’t responsible for the imperfection." (Robert C Martin,"The Clean Coder: A code of conduct for professional programmers", 2011)

"When you cannot concentrate and focus sufficiently, the code you write will be wrong. It will have bugs. It will have the wrong structure. It will be opaque and convoluted. It will not solve the customers’ real problems. In short, it will have to be reworked or redone. Working while distracted creates waste." (Robert C Martin,"The Clean Coder: A code of conduct for professional programmers", 2011)

"Agile teams often do not distinguish between bugs, enhancements, or change requests. They use a general unit called change to track progress. Change seems to be a valid unit for both development and operations because operations teams primarily think in terms of changes to the production system. Using changes as a shared term for both development and operations makes it easier to stream production issues back to a work backlog (that is ideally shared by both groups)." (Michael Hüttermann et al, "DevOps for Developers", 2013)

"Automation is an essential backbone of DevOps. Automation is the use of solutions to reduce the need for human work. Automation can ensure that the software is built the same way each time, that the team sees every change made to the software, and that the software is tested and reviewed in the same way every day so that no defects slip through or are introduced through human error." (Michael Hüttermann et al, "DevOps for Developers", 2013)

"The real bug here is that the design of the system even permits this class of bug. It is unconscionable that someone designing a critical piece of security infrastructure would design the system in such a way that it does not fail safe." (Jamie Zawinski, 2014)

"When you write a computer program you've got to not just list things out and sort of take an algorithm and translate it into a set of instructions. But when there's a bug - and all programs have bugs - you've got to debug it. You've got to go in, change it, and then re-execute … and you iterate. And that iteration is really a very, very good approximation of learning." (Nicholas Negroponte, "A 30-year history of the future", [Ted Talk] 2014)

"Attributing bugs to their authors doesn't make them more responsible, only more scared." (Yegor Bugayenko, "Code Ahead", 2018)

"The job of a tester is to prove that the software is bug free, while it has to be the other way around: The job of a tester is to prove that the software is broken. The better testers are doing their jobs, the more bugs they manage to find and report." (Yegor Bugayenko, "Code Ahead", 2018)

"We must not blame programmers for their bugs. They belong to them only until the code is merged to the repository. After that, all bugs are ours!" (Yegor Bugayenko, "Code Ahead", 2018)

"Fixing a bug is much like adding a new feature: the presence of the bug suggests that a case was missing from the initial test suite, and the bug fix should include that missing test case." (Titus Winters, "Software Engineering at Google: Lessons Learned from Programming Over Time", 2020)

"People are inherently imperfect - we like to say that humans are mostly a collection of intermittent bugs. But before you can understand the bugs in your coworkers, you need to understand the bugs in yourself. We’re going to ask you to think about your own reactions, behaviors, and attitudes - and in return, we hope you gain some real insight into how to become a more efficient and successful software engineer who spends less energy dealing with people-related problems and more time writing great code." (Titus Winters, "Software Engineering at Google: Lessons Learned from Programming Over Time", 2020)

"When program developers are not territorial about their code and encourage others to look for bugs and potential improvements, progress speeds up dramatically." (Gerald Weinberg)

🏗️Software Engineering: Testing (Just the Quotes)

"Program testing can be used to show the presence of bugs, but never to show their absence!" (Edsger W Dijkstra, "Notes On Structured Programming", 1970)

"Test input for validity and plausibility. [...] Make sure input cannot violate the limits of the program. [...] Identify bad input; recover if possible. [...] Test programs at their boundary values." (Brian W Kernighan & Phillip J Plauger, "The Elements of Programming Style", 1974)

"Watch out for off-by-one errors. A common cause of off-by-one errors is an incorrect test, for example using "greater than" when "greater than or equal to" is actually needed. This program is a binary search routine, which looks for a particular element in a table by halving the interval in which the element might lie, until it ultimately either finds it, or deduces that it isn't present." (Brian W Kernighan & Phillip J Plauger, "The Elements of Programming Style", 1974)

"Write and test a big program in small pieces." (Brian W Kernighan & Phillip J Plauger, "The Elements of Programming Style", 1974)

"It is a fundamental principle of testing that you must know in advance the answer each test case is supposed to produce. If you don't, you are not testing; you are experimenting." (Brian Kernighan, "Software Tools in Pascal", 1981)

"The essence of a software entity is a construct of interlocking concepts: […] I believe the hard part of building software to be the specification, design, and testing of this conceptual construct, not the labor of representing it and testing the fidelity of the representation." (Fred Brooks, "No Silver Bullet", 1986)

"Object-oriented programming languages support encapsulation, thereby improving the ability of software to be reused, refined, tested, maintained, and extended. The full benefit of this support can only be realized if encapsulation is maximized during the design process. […] design practices which take a data-driven approach fail to maximize encapsulation because they focus too quickly on the implementation of objects." (Rebecca Wirfs-Brock, "Object-oriented Design: A. responsibility-driven approach", 1989)

"A design remedy that prevents bugs is always preferable to a test method that discovers them." (Boris Beizer, "Software Testing Techniques", 1990)

"A test that reveals a bug has succeeded, not failed." (Boris Beizer, "Software Testing Techniques", 1990)

"More than the act of testing, the act of designing tests is one of the best bug preventers known. The thinking that must be done to create a useful test can discover and eliminate bugs before they are coded - indeed, test-design thinking can discover and eliminate bugs at every stage in the creation of software, from conception to specification, to design, coding and the rest."  (Boris Beizer, "Software Testing Techniques", 1990)

"Programmers are responsible for software quality - quality in their own work, quality in the products that incorporate their work, and quality at the interfaces between components. Quality has never been and will never be tested in. The responsibility is both moral and professional." (Boris Beizer, "Software Testing Techniques", 1990)

"A problem with this 'waterfall' approach is that there will then be no user interface to test with real users until this last possible moment, since the 'intermediate work products' do not explicitly separate out the user interface in a prototype with which users can interact. Experience also shows that it is not possible to involve the users in the design process by showing them abstract specifications documents, since they will not understand them nearly as well as concrete prototypes." (Jakob Nielsen, "Usability Engineering", 1993)

"Testing by itself does not improve software quality. Test results are an indicator of quality, but in and of themselves, they don't improve it. Trying to improve software quality by increasing the amount of testing is like trying to lose weight by weighing yourself more often. What you eat before you step onto the scale determines how much you will weigh, and the software development techniques you use determine how many errors testing will find. If you want to lose weight, don't buy a new scale; change your diet. If you want to improve your software, don't test more; develop better." (Steve C McConnell, "Code Complete: A Practical Handbook of Software Construction", 1993)

"The entire idea behind prototyping is to save on the time and cost to develop something that can be tested with real users. These savings can only be achieved by somehow reducing the prototype compared with the full system: either cutting down on the number of features in the prototype or reducing the level of functionality of the features such that they seem to work but do not actually do anything." (Jakob Nielsen, "Usability Engineering", 1993)

"The real value of tests is not that they detect bugs in the code, but that they detect inadequacies in the methods, concentration, and skills of those who design and produce the code." (Charles A R Hoare, "How Did Software Get So Reliable Without Proof?", Lecture Notes in Computer Science Vol. 1051, 1996)

"The longer we wait between integrations and acceptance tests, the worse things get. Wait twice as long and we'll have four or more times the hassle. The reason is that one bug written just yesterday is pretty easy to find, while ten or a hundred written weeks ago can become almost impossible." (Ron Jeffries, "Extreme Programming Installed", 2001)

"Unit tests can be tedious to write, but they save you time in the future (by catching bugs after changes). Less obviously, but just as important, is that they can save you time now: tests focus your design and implementation on simplicity, they support refactoring, and they validate features as you develop." (Ron Jeffries, "Extreme Programming Installed, 2001)

"People also underestimate the time they spend debugging. They underestimate how much time they can spend chasing a long bug. With testing, I know straight away when I added a bug. That lets me fix the bug immediately, before it can crawl off and hide. There are few things more frustrating or time wasting than debugging. Wouldn't it be a hell of a lot quicker if we just didn't create the bugs in the first place?" (Martin Fowler, 2002)

"A system that is comprehensively tested and passes all of its tests all of the time is a testable system. That’s an obvious statement, but an important one. Systems that aren’t testable aren’t verifiable. Arguably, a system that cannot be verified should never be deployed." (Robert C Martin, "Clean Code: A Handbook of Agile Software Craftsmanship", 2008)

"Features have a specification cost, a design cost, and a development cost. There is a testing cost and a reliability cost. […] Features have a documentation cost. Every feature adds pages to the manual increasing training costs." (Douglas Crockford, "JavaScript: The Good Parts: The Good Parts", 2008)

"If the discipline of requirements specification has taught us anything, it is that well-specified requirements are as formal as code and can act as executable tests of that code!"  (Robert C Martin, "Clean Code: A Handbook of Agile Software Craftsmanship", 2008)

"It is a myth that we can get systems 'right the first time'. Instead, we should implement only today’s stories, then refactor and expand the system to implement new stories tomorrow. This is the essence of iterative and incremental agility. Test-driven development, refactoring, and the clean code they produce make this work at the code level." (Robert C Martin, "Clean Code: A Handbook of Agile Software Craftsmanship", 2008) 

"It is unit tests that keep our code flexible, maintainable, and reusable. The reason is simple. If you have tests, you do not fear making changes to the code! Without tests every change is a possible bug."  (Robert C Martin, "Clean Code: A Handbook of Agile Software Craftsmanship", 2008)

"It turns out that strong typing does not eliminate the need for careful testing. And I have found in my work that the sorts of errors that strong type checking finds are no the errors I worry about." (Douglas Crockford, "JavaScript: The Good Parts", 2008)

"Acceptance testing relies on the ability to execute automated tests in a productionlike environment. However, a vital property of such a test environment is that it is able to successfully support automated testing. Automated acceptance testing is not the same as user acceptance testing. One of the differences is that automated acceptance tests should not run in an environment that includes integration to all external systems. Instead, your acceptance testing should be focused on providing a controllable environment in which the system under test can be run. 'Controllable' in this context means that you are able to create the correct initial state for our tests. Integrating with real external systems removes our ability to do this." (David Farley & Jez Humble, "Continuous Delivery: Reliable Software Releases through Build, Test, and Deployment Automation", 2010)

"In many applications, integration or functional tests are used by default as the standard way to test almost all aspects of the system. However integration and functional tests are not the best way to detect and identify bugs. Because of the large number of components involved in a typical end-to-end test, it can be very hard to know where something has gone wrong. In addition, with so many moving parts, it is extremely difficult, if not completely unfeasible, to cover all of the possible paths through the application." (John F Smart, "Jenkins: The Definitive Guide", 2011)

"Systems with high risks must be tested more thoroughly than systems that do not generate big losses if they fail. The risk assessment must be done for the individual system parts, or even for single error possibilities. If there is a high risk for failures by a system or subsystem, there must be a greater testing effort than for less critical (sub)systems. International standards for production of safety-critical systems use this approach to require that different test techniques be applied for software of different integrity levels." (Andreas Spillner et al, "Software Testing Foundations: A Study Guide for the Certified Tester Exam" 4th Ed., 2014)

"But perhaps the biggest problem is that the longer you spend working on something - whether it’s a prototype or a real product - the more attached you’ll become, and the less likely you’ll be to take negative test results to heart. After one day, you’re receptive to feedback. After three months, you’re committed." (Jake Knapp et al, "Sprint: How to Solve Big Problems and Test New Ideas in Just Five Days", 2016)

"Sometimes you can’t fit everything in. Remember that the sprint is great for testing risky solutions that might have a huge payoff. So you’ll have to reverse the way you would normally prioritize. If a small fix is so good and low-risk that you’re already planning to build it next week, then seeing it in a prototype won’t teach you much. Skip those easy wins in favor of big, bold bets." (Jake Knapp et al, "Sprint: How to Solve Big Problems and Test New Ideas in Just Five Days", 2016)

"Automated testing is a safety net that protects the program from its programmers." (Yegor Bugayenko, "Code Ahead", 2018)

"Quality is a product of a conflict between programmers and testers." (Yegor Bugayenko, "Code Ahead", 2018)

"Quality must be enforced, otherwise it won't happen. We programmers must be required to write tests, otherwise we won't do it." (Yegor Bugayenko, "Code Ahead", 2018)

"The job of a tester is to prove that the software is bug free, while it has to be the other way around: The job of a tester is to prove that the software is broken. The better testers are doing their jobs, the more bugs they manage to find and report." (Yegor Bugayenko, "Code Ahead", 2018)

"Code coverage can provide some insight into untested code, but it is not a substitute for thinking critically about how well your system is tested." (Titus Winters, "Software Engineering at Google: Lessons Learned from Programming Over Time", 2020)

"Fixing a bug is much like adding a new feature: the presence of the bug suggests that a case was missing from the initial test suite, and the bug fix should include that missing test case." (Titus Winters, "Software Engineering at Google: Lessons Learned from Programming Over Time", 2020)

"In addition to developing the proper culture, invest in your testing infrastructure by developing linters, documentation, or other assistance that makes it more difficult to write bad tests." (Titus Winters, "Software Engineering at Google: Lessons Learned from Programming Over Time", 2020)

"When an engineer refactors the internals of a system without modifying its interface, whether for performance, clarity, or any other reason, the system’s tests shouldn’t need to change. The role of tests in this case is to ensure that the refactoring didn’t change the system’s behavior. Tests that need to be changed during a refactoring indicate that either the change is affecting the system’s behavior and isn’t a pure refactoring, or that the tests were not written at an appropriate level of abstraction." (Titus Winters, "Software Engineering at Google: Lessons Learned from Programming Over Time", 2020)

🏗️Software Engineering: Recursion (Just the Quotes)

"A powerful tool for reducing apparent complexity is recursion. In a recursive procedure, the method of solution is defined in terms of itself. That is, each part of the routine handles only a small piece of the strategy, then calls the other parts of the routine as needed to handle the rest. The trick is to reduce each hard case to one that is handled simply elsewhere." (Brian W Kernighan & Phillip J Plauger, "The Elements of Programming Style", 1974)

"Recursion represents no saving of time or storage. Somewhere in the computer must be maintained a list of all the places a recursive routine is called, so the program can eventually find its way back. But the storage for that list is shared among many different uses. More important, it is managed automatically; many of the burdens of storage management and control flow are placed on the compiler, not on the programmer. And since bookkeeping details are hidden, the program can be much easier to understand. Learning to think recursively takes some effort, but it is repaid with smaller and simpler programs." (Brian W Kernighan & Phillip J Plauger, "The Elements of Programming Style", 1974)

"Use recursive procedures for recursively-defined data structures." (Brian W Kernighan & Phillip J Plauger, "The Elements of Programming Style", 1974)

"Recursion is the root of computation since it trades description for time." (Alan J Perlis, "Epigrams on Programming", 1982)

"A deterministic process may be defined in terms of a mathematical function from its input channels to its output channels. Each channel is identified with the indefinitely extensible sequence of messages which pass along it. Such functions are defined in the usual way by recursion on the structure of the input sequences, except that the case of an empty input sequence is not considered." (C Anthony R Hoare, "Communicating Sequential Processes", 1985)

"Recursion permits the definition of a single process as the solution of a single equation. The technique is easily generalised to the solution of sets of simultaneous equations in more than one unknown. For this to work properly, all the right-hand sides must be guarded, and each unknown process must appear exactly once on the left-hand side of one of the equations." (C Anthony R Hoare, "Communicating Sequential Processes", 1985)

"Apart from power laws, iteration is one of the prime sources of self-similarity. Iteration here means the repeated application of some rule or operation - doing the same thing over and over again. […] A concept closely related to iteration is recursion. In an age of increasing automation and computation, many processes and calculations are recursive, and if a recursive algorithm is in fact repetitious, self-similarity is waiting in the wings."(Manfred Schroeder, "Fractals, Chaos, Power Laws Minutes from an Infinite Paradise", 1990)

"When we talk about software architecture, software is recursive and fractal in nature, etched and sketched in code. Everything is details. Interlocking levels of detail also contribute to a building’s architecture, but it doesn’t make sense to talk about physical scale in software. Software has structure - many structures and many kinds of structures-but its variety eclipses the range of physical structure found in buildings. You can even argue quite convincingly that there is more design activity and focus in software than in building architecture - in this sense, it’s not unreasonable to consider software architecture more architectural than building architecture!" (Robert C Martin, "Clean Architecture: A Craftsman's Guide to Software Structure and Design", 2017)

🏗️Software Engineering: Software (Just the Quotes)

"Since software construction is inherently a systems effort - an exercise in complex interrelationships - communication effort is great, and it quickly dominates the decrease in individual task time brought about by partitioning [increasing the workers]. Adding more people then lengthens, not shortens, the schedule." (Frederick Brook, "The Mythical Man-Month", 1975)

"The fundamental problem with software maintenance is that fixing a defect has a substantial (20-50 percent) chance of introducing another. So the whole process is two steps forward and one step back. Why aren't defects fixed more cleanly? First, even a subtle defect shows itself as a local failure of some kind. In fact it often has system-wide ramifications, usually nonobvious. Any attempt to fix it with minimum effort will repair the local and obvious, but unless the structure is pure or the documentation very fine, the far-reaching effects of the repair will be overlooked. Second, the repairer is usually not the man who wrote the code, and often he is a junior programmer or trainee. (Frederick P. Brooks, "The Mythical Man-Month" , 1975)

"The hardest single part of building a software system is deciding precisely what to build." (Frederick P. Brooks, "The Mythical Man-Month", 1975) 

"The essence of a software entity is a construct of interlocking concepts: […] I believe the hard part of building software to be the specification, design, and testing of this conceptual construct, not the labor of representing it and testing the fidelity of the representation." (Fred Brooks, "No Silver Bullet", 1986)

"The finest pieces of software are those where one individual has a complete sense of exactly how the program works. To have that, you have to really love the program and concentrate on keeping it simple, to an incredible degree." (Bill Gates , [interview], 1986)

"There are two ways of constructing a software design. One way is to make it so simple that there are obviously no deficiencies. And the other way is to make it so complicated that there are no obvious deficiencies." (Charles A R Hoare, [lecture] 1987)

"Object-oriented programming languages support encapsulation, thereby improving the ability of software to be reused, refined, tested, maintained, and extended. The full benefit of this support can only be realized if encapsulation is maximized during the design process. […] design practices which take a data-driven approach fail to maximize encapsulation because they focus too quickly on the implementation of objects." (Rebecca Wirfs-Brock, "Object-oriented Design: A. responsibility-driven approach", 1989)

"Programmers are responsible for software quality - quality in their own work, quality in the products that incorporate their work, and quality at the interfaces between components. Quality has never been and will never be tested in. The responsibility is both moral and professional." (Boris Beizer, "Software Testing Techniques", 1990)

"The complexity barrier. Software complexity (and therefore that of bugs) grows to the limits of our ability to manage that complexity." (Boris Beizer, "Software Testing Techniques", 1990)

"The most common kind of coding bug, and often considered the least harmful, are documentation bugs (i.e., erroneous comments). Although many documentation bugs are simple spelling errors or the result of poor writing, many are actual errors - that is, misleading or erroneous comments. We can no longer afford to discount such bugs, because their consequences are as great as 'true' coding errors. Today programming labor is dominated by maintenance. This will increase as software becomes even longer-lived. Documentation bugs lead to incorrect maintenance actions and therefore cause the insertion of other bugs." (Boris Beizer, "Software Testing Techniques", 1990)

"Every software system needs to have a simple yet powerful organizational philosophy (think of it as the software equivalent of a sound bite that describes the system's architecture). [A] step in [the] development process is to articulate this architectural framework, so that we might have a stable foundation upon which to evolve the system's function points." (Grady Booch, "Object-Oriented Design: with Applications", 1991)

"The fundamentals of language are not understood to this day. [...] Until we understand languages of communication involving humans as they are then it is unlikely many of our software problems will vanish." (Richard W Hamming, "The Art of Probability for Scientists and Engineers", 1991)

"As the size of software systems increases, the algorithms and data structures of the computation no longer constitute the major design problems. When systems are constructed from many components, the organization of the overall system - the software architecture - presents a new set of design problems. This level of design has been addressed in a number of ways including informal diagrams and descriptive terms, module interconnection languages, templates and frameworks for systems that serve the needs of specific domains, and formal models of component integration mechanisms." (David Garlan & Mary Shaw, "An introduction to software architecture", Advances in software engineering and knowledge engineering Vol 1, 1993)

"Testing by itself does not improve software quality. Test results are an indicator of quality, but in and of themselves, they don't improve it. Trying to improve software quality by increasing the amount of testing is like trying to lose weight by weighing yourself more often. What you eat before you step onto the scale determines how much you will weigh, and the software development techniques you use determine how many errors testing will find. If you want to lose weight, don't buy a new scale; change your diet. If you want to improve your software, don't test more; develop better." (Steve C McConnell, "Code Complete: A Practical Handbook of Software Construction", 1993)

"Software architecture involves the description of elements from which systems are built, interactions among those elements, patterns that guide their composition, and constraints on these patterns. In general, a particular system is defined in terms of a collection of components and interactions among those components. Such a system may in turn be used as a (composite) element in a larger system design." (Mary Shaw & David Garlan,"Characteristics of Higher-Level Languages for Software Architecture", 1994)

"Our experience with designing and analyzing large and complex software-intensive systems has led us to recognize the role of business and organization in the design of the system and in its ultimate success or failure. Systems are built to satisfy an organization's requirements (or assumed requirements in the case of shrink-wrapped products). These requirements dictate the system's performance, availability, security, compatibility with other systems, and the ability to accommodate change over its lifetime. The desire to satisfy these goals with software that has the requisite properties influences the design choices made by a software architect." (Len Bass et al, "Software Architecture in Practice", 1998)

"Generically, an architecture is the description of the set of components and the relationships between them. […] A software architecture describes the layout of the software modules and the connections and relationships among them. A hardware architecture can describe how the hardware components are organized. However, both these definitions can apply to a single computer, a single information system, or a family of information systems. Thus 'architecture' can have a range of meanings, goals, and abstraction levels, depending on who’s speaking." (Frank J Armour et al, "A big-picture look at enterprise architectures", IT professional Vol 1 (1), 1999)

"Planning is not about predicting the future. When you make a plan for developing a piece of software, development is not going to go like that. Not ever. Your customers wouldn’t even be happy if it did, because by the time software gets there, the customers don’t want what was planned, they want something different." (Kent Beck & Martin Fowler, "Planning Extreme Programming", 2000)

"Design patterns provide the cores of ready-made solutions that can be used to solve many of software’s most common problems. Some software problems require solutions that are derived from first principles. But most problems are similar to past problems, and those can be solved using similar solutions, or patterns." (Steve C McConnell, "Code Complete: A Practical Handbook of Software Construction" 2nd Ed., 2004)

"The software architecture of a system or a family of systems has one of the most significant impacts on the quality of an organization's enterprise architecture. While the design of software systems concentrates on satisfying the functional requirements for a system, the design of the software architecture for systems concentrates on the nonfunctional or quality requirements for systems. These quality requirements are concerns at the enterprise level. The better an organization specifies and characterizes the software architecture for its systems, the better it can characterize and manage its enterprise architecture. By explicitly defining the systems software architectures, an organization will be better able to reflect the priorities and trade-offs that are important to the organization in the software that it builds." (James McGovern et al, "A Practical Guide to Enterprise Architecture", 2004)

"A road plan can show the exact location, elevation, and dimensions of any part of the structure. The map corresponds to the structure, but it's not the same as the structure. Software, on the other hand, is just a codification of the behaviors that the programmers and users want to take place. The map is the same as the structure. […] This means that software can only be described accurately at the level of individual instructions. […] A map or a blueprint for a piece of software must greatly simplify the representation in order to be comprehensible. But by doing so, it becomes inaccurate and ultimately incorrect. This is an important realization: any architecture, design, or diagram we create for software is essentially inadequate. If we represent every detail, then we're merely duplicating the software in another form, and we're wasting our time and effort." (George Stepanek, "Software Project Secrets: Why Software Projects Fail", 2005)

"Software is abstract and therefore seems as if it should be infinitely malleable. And yet, for all its ethereal flexibility, it can be stubbornly, maddeningly intractable, and it is constantly surprising us with its rigidity." (Scott Rosenberg, "Dreaming in Code", 2007)

"Software is different; it has no core. It is onionlike, a thing of layers, each built painstakingly and precariously on the previous one, each counting on the one below not to move or change too much. Software builders like to talk about laying bricks; skeptics see a house of cards. Either way, there’s a steady accumulation going on. New layers pile on old. Programmers call these accretions 'layers of abstraction', because each time a new one is added, something complex and specific is being translated into something simpler and more general." (Scott Rosenberg, "Dreaming in Code", 2007)

"Software is easy to make, except when you want it to do something new. And then, of course, there is a corollary: The only software that's worth making is software that does something new." (Scott Rosenberg, "Dreaming in Code", 2007)

"The names programmers adopt for their abstractions are, as geeks like to say, 'nontrivial'. In software, labels and names matter; they are the handles by which you grab things." (Scott Rosenberg, "Dreaming in Code", 2007)

"There is almost always something you can pull off the shelf that will satisfy many of your needs. But usually the parts of what you need done that your off-the-shelf code won’t handle are the very parts that make your new project different, unique, innovative - and they’re why you’re building it in the first place." (Scott Rosenberg, "Dreaming in Code", 2007)

"We tend to form mental models that are simpler than reality; so if we create represented models that are simpler than the actual implementation model, we help the user achieve a better understanding. […] Understanding how software actually works always helps someone to use it, but this understanding usually comes at a significant cost. One of the most significant ways in which computers can assist human beings is by putting a simple face on complex processes and situations. As a result, user interfaces that are consistent with users’ mental models are vastly superior to those that are merely reflections of the implementation model." (Alan Cooper et al,  "About Face 3: The Essentials of Interaction Design", 2007)

"Part of the beauty of software is that it’s deterministic - the computer does exactly what you tell it to do, and, given the same starting point, it will do exactly the same thing every time." (Paul Butcher, "Debug It! Find, Repair, and Prevent Bugs in Your Code", 2009)

"Writing and (particularly) maintaining software is a continual battle against entropy. Keeping on top of quality is tough, requiring high levels of discipline. This discipline is difficult enough to maintain under the best of circumstances, let alone when faced with concrete evidence that the software is uncared for, such as a long-unfixed bug. As soon as discipline slips, quality can go into a self-reinforcing downward spiral, and you’re in real trouble." (Paul Butcher, "Debug It! Find, Repair, and Prevent Bugs in Your Code", 2009)

"We developers can easily develop blind spots. We necessarily have a different perspective from our users, and that can mean we miss important information that would be obvious to someone who understands things from their point of view. Furthermore, our focus tends to be on working out how to make the software work, not proving that it’s broken." (Paul Butcher, "Debug It! Find, Repair, and Prevent Bugs in Your Code", 2009)

"Refactoring is the process of changing a software system in such a way that it does not alter the external behavior of the code yet improves its internal structure. It is a disciplined way to clean up code that minimizes the chances of introducing bugs. In essence when you refactor you are improving the design of the code after it has been written." (Jay Fields et al, "Refactoring: Ruby Edition", 2010)

"An obsession with 'feature delivery' ignores the human-related and team-related dynamics inherent in modern software, leading to a lack of engagement from staff, especially when the cognitive load is exceeded." (Matthew Skelton, "Team Topologies: Organizing Business and Technology Teams for Fast Flow", 2019)

"Trying to determine the cognitive load of software using simple measures such as lines of code, number of modules, classes, or methods is misguided. […] When measuring cognitive load, what we really care about is the domain complexity - how complex is the problem that we’re trying to solve with software? A domain is a more largely applicable concept than software size." (Matthew Skelton, "Team Topologies: Organizing Business and Technology Teams for Fast Flow", 2019)

"One of the great enemies of design is when systems or objects become more complex than a person - or even a team of people - can keep in their heads. This is why software is generally beneath contempt." (Bran Ferren)

"The thing that makes software design difficult is that we must express thoughts about a problem and a solution we typically do not understand fully, using a language that does not contain many of our accustomed features of expression, to a system that is unforgiving of mistakes." (Alistair Cockburn)

🏗️Software Engineering: Refactoring (Just the Quotes)

"When you feel the need to write a comment, first try to refactor the code so that any comment becomes superfluous." (Kent Beck, "Refactoring: Improving the Design of Existing Code", 1999)

"When you find you have to add a feature to a program, and the program's code is not structured in a convenient way to add the feature, first refactor the program to make it easy to add the feature, then add the feature."  (Kent Beck, "Refactoring: Improving the Design of Existing Code", 1999)

"Unit tests can be tedious to write, but they save you time in the future (by catching bugs after changes). Less obviously, but just as important, is that they can save you time now: tests focus your design and implementation on simplicity, they support refactoring, and they validate features as you develop." (Ron Jeffries, "Extreme Programming Installed, 2001)

"Before you start refactoring, check that you have a solid suite of tests. These tests must be self-checking." (Martin Fowler et al, "Refactoring: Improving the Design of Existing Code", 2002)

"Given software engineers’ infatuation with indirection, it may not surprise you to learn that most refactoring introduces more indirection into a program. Refactoring tends to break big objects into several smaller ones and big methods into several smaller ones." (Kent Beck, "Indirection and Refactoring", 2002)

"One problem area for refactoring is databases. Most business applications are tightly coupled to the database schema that supports them. That's one reason that the database is difficult to change. Another reason is data migration. Even if you have carefully layered your system to minimize the dependencies between the database schema and the object model, changing the database schema forces you to migrate the data, which can be a long and fraught task." (Martin Fowler et al, "Refactoring: Improving the Design of Existing Code", 2002)

"Refactoring is risky. It requires changes to working code that can introduce subtle bugs. Refactoring, if not done properly, can set you back days, even weeks. And refactoring becomes riskier when practiced informally or ad hoc." (Erich Gamma, 2002)

"Refactoring is the process of changing a software system in such a way that it does not alter the external behavior of the code yet improves its internal structure. It is a disciplined way to clean up code that minimizes the chances of introducing bugs. In essence when you refactor you are improving the design of the code after it has been written." (Martin Fowler et al, "Refactoring: Improving the Design of Existing Code", 2002)

"Refactoring is the process of taking a running program and adding to its value, not by changing its behavior but by giving it more of these qualities that enable us to continue developing at speed." (Kent Beck, "Why Refactoring Works", 2002)

"Refactoring changes the programs in small steps. If you make a mistake, it is easy to find the bug." (Martin Fowler et al, "Refactoring: Improving the Design of Existing Code", 2002)

"Without refactoring, the design of the program will decay. As people change code - changes to realize short-term goals or changes made without a full comprehension of the design of the code - the code loses its structure. It becomes harder to see the design by reading the code. Refactoring is rather like tidying up the code. Work is done to remove bits that aren't really in the right place. Loss of the structure of code has a cumulative effect. The harder it is to see the design in the code, the harder it is to preserve it, and the more rapidly it decays. Regular refactoring helps code retain its shape." (Martin Fowler et al, "Refactoring: Improving the Design of Existing Code", 2002)

"A commitment to simplicity of design means addressing the essence of design - the abstractions on which software is built - explicitly and up front. Abstractions are articulated, explained, reviewed and examined deeply, in isolation from the details of the implementation. This doesn’t imply a waterfall process, in which all design and specification precedes all coding. But developers who have experienced the benefits of this separation of concerns are reluctant to rush to code, because they know that an hour spent on designing abstractions can save days of refactoring." (Daniel Jackson, "Software Abstractions", 2006)

"To programmers, refactoring means rewriting a chunk of code to make it briefer, clearer, and easier to read without changing what it actually does. Refactoring is often compared to gardening; it is never finished." (Scott Rosenberg, "Dreaming in Code", 2007)

"It is a myth that we can get systems 'right the first time'. Instead, we should implement only today’s stories, then refactor and expand the system to implement new stories tomorrow. This is the essence of iterative and incremental agility. Test-driven development, refactoring, and the clean code they produce make this work at the code level." (Robert C Martin, "Clean Code: A Handbook of Agile Software Craftsmanship", 2008)

"Refactoring is a lot like solving a Rubik’s cube. There are lots of little steps required to achieve a large goal. Each step enables the next." (Robert C Martin, "Clean Code: A Handbook of Agile Software Craftsmanship", 2008)

"Refactoring is the process of improving the design of existing code without changing its behavior. [...] Bug fixing often uncovers opportunities for refactoring. The very fact that you’re working with code that contains a bug indicates that there is a chance that it could be clearer or better structured." (Paul Butcher, "Debug It! Find, Repair, and Prevent Bugs in Your Code", 2009)

"Although it is focused on the code, refactoring has a large impact on the design of a system. It is vital for senior designers and architects to understand the principles of refactoring and to use them in their projects." (Jay Fields et al, "Refactoring: Ruby Edition", 2010)

"Refactoring is the process of changing a software system in such a way that it does not alter the external behavior of the code yet improves its internal structure. It is a disciplined way to clean up code that minimizes the chances of introducing bugs. In essence when you refactor you are improving the design of the code after it has been written." (Jay Fields et al, "Refactoring: Ruby Edition", 2010)

"When an engineer refactors the internals of a system without modifying its interface, whether for performance, clarity, or any other reason, the system’s tests shouldn’t need to change. The role of tests in this case is to ensure that the refactoring didn’t change the system’s behavior. Tests that need to be changed during a refactoring indicate that either the change is affecting the system’s behavior and isn’t a pure refactoring, or that the tests were not written at an appropriate level of abstraction." (Titus Winters, "Software Engineering at Google: Lessons Learned from Programming Over Time", 2020)

🏗️Software Engineering: Software Development (Just the Quotes)

"Far be it from me to suggest that all changes in customer objectives and requirements must, can, or should be incorporated in the design. Clearly a threshold has to be established, and it must get higher and higher as development proceeds, or no product ever appears." (Fred P Brooks, "The Mythical Man-Month: Essays", 1975)

"Economic principles underlie the overall structure of the software lifecycle, and its primary refinements of prototyping, incremental development, and advancemanship. The primary economic driver of the life-cycle structure is the significantly increasing cost of making a software change or fixing a software problem, as a function of the phase in which the change or fix is made." (Barry Boehm, "Software Engineering Economics", 1981)

"Poor management can increase software costs more rapidly than any other factor. Particularly on large projects, each of the following mismanagement actions has often been responsible for doubling software development costs." (Barry Boehm, "Software Engineering Economics", 1981)

"The primary functions of a software process model are to determine the order of the stages involved in software development and evolution and to establish the transition criteria for progressing from one Stage to the next. These include completion criteria for the current stage plus choice criteria and entrance criteria for the next stage. Thus, a process model addresses the following software project questions: (1) What shall we do next? (2) How long shall we continue to do it?" (Barry Boehm, "A spiral model of software development and enhancement", IEEE, 1988)

"Every software system needs to have a simple yet powerful organizational philosophy (think of it as the software equivalent of a sound bite that describes the system's architecture). [A] step in [the] development process is to articulate this architectural framework, so that we might have a stable foundation upon which to evolve the system's function points." (Grady Booch, "Object-Oriented Design: with Applications", 1991)

"Testing by itself does not improve software quality. Test results are an indicator of quality, but in and of themselves, they don't improve it. Trying to improve software quality by increasing the amount of testing is like trying to lose weight by weighing yourself more often. What you eat before you step onto the scale determines how much you will weigh, and the software development techniques you use determine how many errors testing will find. If you want to lose weight, don't buy a new scale; change your diet. If you want to improve your software, don't test more; develop better." (Steve C McConnell, "Code Complete: A Practical Handbook of Software Construction", 1993)

"If a project has not achieved a system architecture, including its rationale, the project should not proceed to full-scale system development. Specifying the architecture as a deliverable enables its use throughout the development and maintenance process." (Barry Boehm, 1995)

"Successful software development is a team effort - not just the development team, but the larger team consisting of customer, management and developers. [...] Every software project needs to deliver business value. To be successful, the team needs to build the right things, in the right order, and to be sure that what they build actually works." (Ron Jeffries, "Extreme Programming Installed", 2001)

"Agile development methodologies promise higher customer satisfaction, lower defect rates, faster development times and a solution to rapidly changing requirements. Plan-driven approaches promise predictability, stability, and high assurance. However, both approaches have shortcomings that, if left unaddressed, can lead to project failure. The challenge is to balance the two approaches to take advantage of their strengths and compensate for their weaknesses." (Barry Boehm & Richard Turner, "Observations on balancing discipline and agility", Agile Development Conference, 2003)

"Computer programming is tremendous fun. Like music, it is a skill that derives from an unknown blend of innate talent and constant practice. Like drawing, it can be shaped to a variety of ends – commercial, artistic, and pure entertainment. Programmers have a well-deserved reputation for working long hours, but are rarely credited with being driven by creative fevers. Programmers talk about software development on weekends, vacations, and over meals not because they lack imagination, but because their imagination reveals worlds that others cannot see." (Larry O'Brien & Bruce Eckel, "Thinking in C#", 2003)

"Design patterns give names to practical knowledge; they define a high-level vocabulary for understanding and solving business statements graphically. Design patterns are presented in a standard format; they're like recipes in a cookbook or dress patterns in a catalog. Above all, they are practical, first as instructional materials and then as development tools." (Alan Chmura & J Mark Heumann, "Logical Data Modeling: What it is and How to do it", 2005)

"Developing fewer features allows you to conserve development resources and spend more time refining those features that users really need. Fewer features mean fewer things to confuse users, less risk of user errors, less description and documentation, and therefore simpler Help content. Removing any one feature automatically increases the usability of the remaining ones." (Jakob Nielsen, "Prioritizing Web Usability", 2006)

"Communicating abstractions unambiguously - from programmer to machine, from programmer to programmer, and from program to user - is the single most challenging demand of software development." (Scott Rosenberg, "Dreaming in Code", 2007)

"[…] in software development, as in all things, plans get dodgier the farther into the future one looks. Any developer who has been around the block will admit that the cavalcade of methodologies over three decades of software history has left the field richer and given programmers useful new tools and ways of thinking about their work. But finding a developer or team that actually subscribes to a particular methodology isn’t easy." (Scott Rosenberg, "Dreaming in Code", 2007)

"The amateur software engineer is always in search of magic, some sensational method or tool whose application promises to render software development trivial. It is the mark of the professional software engineer to know that no such panacea exist." (Grady Booch et al, "Object-Oriented Analysis and Design with Applications", 2007) 

"The picture of digital progress that so many ardent boosters paint ignores the painful record of actual programmers’ epic struggles to bend brittle code into functional shape. That record is of one disaster after another, marking the field’s historical time line like craters. Anyone contemplating the start of a big software development project today has to contend with this unfathomably discouraging burden of experience. It mocks any newcomer with ambitious plans, as if to say, What makes you think you’re any different?" (Scott Rosenberg, "Dreaming in Code", 2007)

"Features have a specification cost, a design cost, and a development cost. There is a testing cost and a reliability cost. […] Features have a documentation cost. Every feature adds pages to the manual increasing training costs." (Douglas Crockford, "JavaScript: The Good Parts: The Good Parts", 2008)

"It is a myth that we can get systems 'right the first time'. Instead, we should implement only today’s stories, then refactor and expand the system to implement new stories tomorrow. This is the essence of iterative and incremental agility. Test-driven development, refactoring, and the clean code they produce make this work at the code level." (Robert C Martin, "Clean Code: A Handbook of Agile Software Craftsmanship", 2008)

"The use of rapid prototyping methodologies is to reduce the production time by using working models of the final product early in a project tends to eliminate time-consuming revisions later on, and by completing design tasks concurrently, rather than sequentially throughout the project. The steps are crunched together to reduce the amount of time needed to develop training or a product. The design and development phases are done simultaneously and the formative evaluation is done throughout the process." (Irene Chen, "Instructional Design Methodologies", 2008)

"Agile approaches to software development consider design and implementation to be the central activities in the software process. They incorporate other activities, such as requirements elicitation and testing, into design and implementation. By contrast, a plan-driven approach to software engineering identifies separate stages in the software process with outputs associated with each stage." (Ian Sommerville, "Software Engineering" 9th Ed., 2011)

"Agile methods universally rely on an incremental approach to software specification, development, and delivery. They are best suited to application development where the system requirements usually change rapidly during the development process. They are intended to deliver working software quickly to customers, who can then propose new and changed requirements to be included in later iterations of the system. They aim to cut down on process bureaucracy by avoiding work that has dubious long-term value and eliminating documentation that will probably never be used." (Ian Sommerville, "Software Engineering" 9th Ed., 2011)

"Software development is a marathon, not a sprint. You can’t win the race by trying to run as fast as you can from the outset. You win by conserving your resources and pacing yourself. A marathon runner takes care of her body both before and during the race. Professional programmers conserve their energy and creativity with the same care." (Robert C Martin,"The Clean Coder: A code of conduct for professional programmers", 2011) 

"System engineering is concerned with all aspects of the development and evolution of complex systems where software plays a major role. System engineering is therefore concerned with hardware development, policy and process design and system deployment, as well as software engineering. System engineers are involved in specifying the system, defining its overall architecture, and then integrating the different parts to create the finished system. They are less concerned with the engineering of the system components (hardware, software, etc.)." (Ian Sommerville, "Software Engineering" 9th Ed., 2011)

"A value stream is a series of activities required to deliver an outcome. The software development value stream may be described as: validate business case, analyze, design, build, test, deploy, learn from usage analytics and other feedback - rinse and repeat." (Sriram Narayan, "Agile IT Organization Design: For Digital Transformation and Continuous Delivery", 2015)

"Development is a design process. Design processes are generally evaluated by the value they deliver rather than a conformance to plan. Therefore, it makes sense to move away from plan-driven projects and toward value-driven projects. […] The realization that the source code is part of the design, not the product, fundamentally rewires our understanding of software." (Sriram Narayan, "Agile IT Organization Design: For Digital Transformation and Continuous Delivery", 2015)

"DevOps recognizes the importance of culture. The acronym CAMS (culture, automation, measurement, and sharing) is used to encapsulate its key themes. Culture is acknowledged as all important in making development and IT operations work together effectively. But what is culture in this context? It is not so much about an informal dress code, flexible hours, or a free in-house cafeteria as it is about how decisions are taken, norms of behavior, protocols of communication, and the ways of navigating hierarchy and bureaucracy to get things done." (Sriram Narayan, "Agile IT Organization Design: For Digital Transformation and Continuous Delivery", 2015)

"Feedback is what makes it iterative; otherwise, it is just mini-waterfall. Merely splitting use cases into stories does not make for iterative development if we wait until all stories are developed before we seek feedback. The point of splitting is to get feedback faster so that it can be incorporated into ongoing development. However, seeking stakeholder/user feedback for small batches of functionality (stories) is often not feasible with formal stage-gate processes. They were conceived with linear flows of large batches in mind." (Sriram Narayan, "Agile IT Organization Design: For Digital Transformation and Continuous Delivery", 2015)

"A key contribution of DevOps was to raise awareness of the problems lingering in how teams interacted (or not) across the delivery chain, causing delays, rework, failures, and a lack of understanding and empathy toward other teams. It also became clear that such issues were not only happening between application development and operations teams but in interactions with many other teams involved in software delivery, like QA, InfoSec, networking, and more." (Matthew Skelton & Manuel Pais, "Team Topologies: Organizing Business and Technology Teams for Fast Flow", 2019)

🏗️Software Engineering: Data Migration (Just the Quotes)

"One problem area for refactoring is databases. Most business applications are tightly coupled to the database schema that supports them. That's one reason that the database is difficult to change. Another reason is data migration. Even if you have carefully layered your system to minimize the dependencies between the database schema and the object model, changing the database schema forces you to migrate the data, which can be a long and fraught task." (Martin Fowler et al, "Refactoring: Improving the Design of Existing Code", 2002)

"Data migration is not just about moving data from one place to another; it should be focused on: realizing all the benefits promised by the new system when you entertained the concept of new software in the first place; creating the improved enterprise performance that was the driver for the project; importing the best, the most appropriate and the cleanest data you can so that you enhance business intelligence; maintaining all your regulatory, legal and governance compliance criteria; staying securely in control of the project." (John Morris, "Practical Data Migration", 2009)

 "One of my criticisms of the usual ad hoc approach to data migration is that it does not contain standardized work packages that allow for the migration activity to be tracked at programme level. Breaking data cleansing, the principal activity, down into methods and tasks allows different levels of control by the programme office." (John Morris, "Practical Data Migration", 2009)

"The key to a successful migration is to remember that data migration is a business not a technical problem and data quality is a business not a technical issue. It is for the enterprise to dictate how and where data comes from and goes and what constitutes sufficient data quality. It is our jobs, as handmaidens of progress, to assist with the technical issues of moving data from one place to another, identifying referential integrity and other technical issues, and facilitating the process. But we are the servants not the masters." (John Morris, "Practical Data Migration", 2009)

"Data migration is indeed a complex project. It is common for companies to underestimate the amount of time it takes to complete the data conversion successfully. Data quality usually suffers because it is the first thing to be dropped once the project is behind schedule. Make sure to allocate enough time to complete the task maintaining the highest standards of quality necessary. Migrate now, clean later typically leads to another source of mistrusted data, defeating the whole purpose of MDM." (Dalton Cervo & Mark Allen, "Master Data Management in Practice: Achieving true customer MDM", 2011)

"Data migration, in simple terms, is about physically copying data from one repository into another. The need for a data migration effort is highly dependent on the MDM architecture chosen [...] The goal of MDM is to eliminate redundant systems and have a single system-of-record. Therefore, it seems contradictory to have a temporary ongoing data migration, which is, in essence, maintaining multiple systems and having to write additional software to keep them synchronized." (Dalton Cervo & Mark Allen, "Master Data Management in Practice: Achieving true customer MDM", 2011)

"Companies typically underestimate the importance of metadata management in general, and more specifically during data migration projects. Metadata management is normally postponed when data migration projects are behind schedule because it doesn’t necessarily provide immediate benefit. However, in the long run, it becomes critical. It is common to see data issues later, and without proper metadata or data lineage it becomes difficult to assess the root cause of the problem." (Dalton Cervo & Mark Allen, "Master Data Management in Practice: Achieving true customer MDM", 2011)

"For a metadata management program to be successful, it needs to be accessible to everybody that needs it, either from a creation or a consumption perspective. It should also be readily available to be used as a byproduct of other activities, such as data migration and data cleansing. Remember, metadata is documentation, and the closer it is generated to the activity affecting it, the better." (Dalton Cervo & Mark Allen, "Master Data Management in Practice: Achieving true customer MDM", 2011)

🏗️Software Engineering: Design Patterns (Just the Quotes)

"A pattern is a fully realized form original, or model accepted or proposed for imitation. With patterns, small piecework is standardized into a larger chunk or unit. Patterns become the building blocks for design and construction. Finding and applying patterns indicates progress in a field of human endeavor." (Peter Coad, "Object-oriented patterns", 1992) 

"A design pattern systematically names, motivates, and explains a general design that addresses a recurring design problem in object-oriented systems. It describes the problem, the solution, when to apply the solution, and its consequences. It also gives implementation hints and examples. The solution is a general arrangement of objects and classes that solve the problem. The solution is customized and implemented to solve the problem in a particular context." (Erich Gamma et al, "Design Patterns: Elements of Reusable Object-Oriented Software", 1994)

"The purpose of a conceptual model is to provide a vocabulary of terms and concepts that can be used to describe problems and/or solutions of design. It is not the purpose of a model to address specific problems, and even less to propose solutions for them. Drawing an analogy with linguistics, a conceptual model is analogous to a language, while design patterns are analogous to rhetorical figures, which are predefined templates of language usages, suited particularly to specific problems." (Peter P Chen [Ed.], "Advances in Conceptual Modeling", 1999)

"In addition to their complexity-management benefit, design patterns can accelerate design discussions by allowing designers to think and discuss at a larger level of granularity." (Steve McConnell, "Code Complete" 2nd Ed., 2004)

"On small, informal projects, a lot of design is done while the programmer sits at the keyboard. 'Design' might be just writing a class interface in pseudocode before writing the details. It might be drawing diagrams of a few class relationships before coding them. It might be asking another programmer which design pattern seems like a better choice. Regardless of how it’s done, small projects benefit from careful design just as larger projects do, and recognizing design as an explicit activity maximizes the benefit you will receive from it." (Steve McConnell, "Code Complete" 2nd Ed., 2004)

"Software design patterns are what allow us to describe design fragments, and reuse design ideas, helping developers leverage the expertise of others. Patterns give a name and form to abstract heuristics, rules and best practices of object-oriented techniques." (Philippe Kruchten, [foreword] 2004)

"Design patterns give names to practical knowledge; they define a high-level vocabulary for understanding and solving business statements graphically. Design patterns are presented in a standard format; they're like recipes in a cookbook or dress patterns in a catalog. Above all, they are practical, first as instructional materials and then as development tools." (Alan Chmura & J Mark Heumann, "Logical Data Modeling: What it is and How to do it", 2005)

"Structural patterns describe how classes and objects can be combined to form larger structures. Patterns for classes describe how inheritance can be used to provide more useful program interfaces. Patterns for objects describe how objects can be composed into larger structures using object composition." (Junji Nakano et al, "Programming Statistical Data Visualization in the Java Language" [in "Handbook of Data Visualization"], 2008)

"Design patterns are high-level abstractions that document successful design solutions. They are fundamental to design reuse in object-oriented development." (Ian Sommerville, "Software Engineering" 9th Ed., 2011)

"Most designers think of design patterns as a way of supporting object-oriented design. Patterns often rely on object characteristics such as inheritance and polymorphism to provide generality. However, the general principle of encapsulating experience in a pattern is one that is equally applicable to all software design approaches." (Ian Sommerville, "Software Engineering" 9th Ed., 2011)

"A design pattern usually suggests a scheme for structuring the classes in a design solution and defines the required interactions among those classes. In other words, a design pattern describes some commonly recurring structure of communicating classes that can be used to solve some general design problems. Design pattern solutions are typically described in terms of classes, their instances, their roles and collaborations." (Rajib Mall, "Fundamentals of Software Engineering" 4th Ed., 2014)

"If a pattern represents a best practice, then an antipattern represents lessons learned from a bad design. [...] Antipatterns are valuable because they help us to recognise why a particular design alternative might seem at first like an attractive solution, but later on lead to complicacies and finally turn out to be a poor solution." (Rajib Mall, "Fundamentals of Software Engineering" 4th Ed., 2014)

"Each pattern describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice.''  (Christopher Alexander)