31 December 2007

Software Engineering: Architecture (Just the Quotes)

"The term architecture is used here to describe the attributes of a system as seen by the programmer, i.e., the conceptual structure and functional behavior, as distinct from the organization of the data flow and controls, the logical design, and the physical implementation." (Gene Amdahl et al, "Architecture of the IBM System", IBM Journal of Research and Development. Vol 8 (2), 1964)

"In computer design three levels can be distinguished: architecture, implementation and realisation; for the first of them, the following working definition is given: The architecture of a system can be defined as the functional appearance of the system to the user, its phenomenology. […] The inner structure of a system is not considered by the architecture: we do not need to know what makes the clock tick, to know what time it is. This inner structure, considered from a logical point of view, will be called the implementation, and its physical embodiment the realisation." (Gerrit A Blaauw, "Computer Architecture", 1972)

"There always is an architecture, whether it is defined in advance - as with modern computers - or found out after the fact - as with many older computers. For architecture is determined by behavior, not by words. Therefore, the term architecture, which rightly implies the notion of the arch, or prime structure, should not be understood as the vague overall idea. Rather, the product of the computer architecture, the principle of operations manual, should contain all detail which the user can know, and sooner or later is bound to know." (Gerrit A Blaauw, "Computer Architecture", 1972)

"The design of a digital system starts with the specification of the architecture of the system and continues with its implementation and its subsequent realisation... the purpose of architecture is to provide a function. Once that function is established, the purpose of implementation is to give a proper cost-performance and the purpose of realisation is to build and maintain the appropriate logical organisation." (Gerrit A Blaauw, "Specification of Digital Systems", Proc. Seminar in Digital Systems Design, 1978)

"With increasing size and complexity of the implementations of information systems, it is necessary to use some logical construct (or architecture) for defining and controlling the interfaces and the integration of all of the components of the system." (John Zachman, "A Framework for Information Systems Architecture", 1987)

"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)

"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)

"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)

"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)

"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)

"An architecture framework is a tool which can be used for developing a broad range of different architectures [architecture descriptions]. It should describe a method for designing an information system in terms of a set of building blocks, and for showing how the building blocks fit together. It should contain a set of tools and provide a common vocabulary. It should also include a list of recommended standards and compliant products that can be used to implement the building blocks." (TOGAF, 2002)

"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)

"The traditional view on software architecture suffers from a number of key problems that cannot be solved without changing our perspective on the notion of software architecture. These problems include the lack of first-class representation of design decisions, the fact that these design decisions are cross-cutting and intertwined, that these problems lead to high maintenance cost, because of which design rules and constraints are easily violated and obsolete design decisions are not removed." (Jan Bosch, "Software architecture: The next step", 2004)

"As a noun, design is the named (although sometimes unnamable) structure or behavior of a system whose presence resolves or contributes to the resolution of a force or forces on that system. A design thus represents one point in a potential decision space. A design may be singular (representing a leaf decision) or it may be collective (representing a set of other decisions). As a verb, design is the activity of making such decisions. Given a large set of forces, a relatively malleable set of materials, and a large landscape upon which to play, the resulting decision space may be large and complex. As such, there is a science associated with design (empirical analysis can point us to optimal regions or exact points in this design space) as well as an art (within the degrees of freedom that range beyond an empirical decision; there are opportunities for elegance, beauty, simplicity, novelty, and cleverness). All architecture is design but not all design is architecture. Architecture represents the significant design decisions that shape a system, where significant is measured by cost of change." (Grady Booch, "On design", 2006)

"The goal for our software architecture is to provide the key mechanisms that are required to implement a wide variety of cross-layer adaptations described by our taxonomy. Our strategy for developing such an architecture is actually to create two architectures, a 'conceptual' one, followed by a 'concrete' one." (Soon H Choi, "A Software Architecture for Cross-layer Wireless Networks", 2008)

"A good system design is based on a sound conceptual model (architecture). A system design that has no conceptual structure and little logic to its organization is ultimately going to be unsuccessful. Good architecture will address all the requirements of the system at the right level of abstraction." (Vasudeva Varma, "Software Architecture: A Case Based Approach", 2009)

"A software architecture encompasses the significant decisions about the organization of the software system, the selection of structural elements and interfaces by which the system is composed, and determines their behavior through collaboration among these elements and their composition into progressively larger subsystems. Hence, the software architecture provides the skeleton of a system around which all other aspects of a system revolve." (Muhammad A Babar et al, "Agile Software Architecture Aligning Agile Processes and Software Architectures", 2014)

"Good architecture is all about splitting stuff reliably into self-contained parcels that allow work on them to continue relatively independently in parallel (often these days in different locations)." (Richard Hopkins & Stephen Harcombe, "Agile Architecting: Enabling the Delivery of Complex Agile Systems Development Projects", 2014)

"Good architecture provides good interfaces that separate the shear layers of its implementation: a necessity for evolution and maintenance. Class-oriented programming puts both data evolution and method evolution in the same shear layer: the class. Data tend to remain fairly stable over time, while methods change regularly to support new services and system operations. The tension in these rates of change stresses the design." (James O Coplien & Trygve Reenskaug, "The DCI Paradigm: Taking Object Orientation into the Architecture World", 2014)

"In more ways than one, architecture is all about avoiding bottlenecks. In architecture, the term bottleneck typically refers to a design problem that is preventing processing from occurring at full speed. [...] A good architecture will avoid bottlenecks in both." (Richard Hopkins & Stephen Harcombe, "Agile Architecting: Enabling the Delivery of Complex Agile Systems Development Projects", 2014)

"There is a tendency to believe that good architecture leads to systems that perform better and are more secure, but such claims relate less to any given architectural principle than to the timing of big-picture deliberations in the design cycle and to the proper engagement of suitable stakeholders." (James O Coplien & Trygve Reenskaug, "The DCI Paradigm: Taking Object Orientation into the Architecture World", 2014)

"Architecture begins where engineering ends." (Walter Gropius, [speech])

"Architecture is the tension between coupling and cohesion." (Neal Ford)

"Programming without an overall architecture or design in mind is like exploring a cave with only a flashlight: You don't know where you've been, you don't know where you're going, and you don't know quite where you are." (Danny Thorpe)

"The fundamental organization of a system embodied in its components, their relationships to each other, and to the environment, and the principles guiding its design and evolution." (ANSI/IEEE Std 1471: 2000)

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