"The database is the heart of our information processing systems and not simply a by-product of processing. […] A database that has been properly structured and organized, and which actually represents and contains that data of an enterprise, will stabilize the information processing systems. [...] The use of data is reckoning, the generation of information which will in turn be used to manage the enterprise. The generation of information is the only reason for having a database." (John K Lyon, "What is a Data Base", Bulletin of ACM SIGFIDET 5(1) , 1973)
"A database has structure which exists in three forms. It has a perceived structure, which is the way that each of us looks at the database. […] The physical structure of the database relates to the manner in which data is physically represented within the database in terms of sort sequence, record and field sizes, and its existence on one or more master files. […] The logical structure describes the way things really exist within the environment. The entities, i.e., the things within the enterprise, really exist; they have properties which distinguish them from all the other things within the business; and the relationships which exist among the entities." (John K Lyon, "What is a Data Base", Bulletin of ACM SIGFIDET 5(1) , 1973)
"Two of the most difficult areas of data-base management are the design of an information structure and the reduction of that structure to a data structure which is compatible with and managed by the DBMS. […] Data-base management systems are tools to be applied by the users of these systems to build an accurate and useful model of their organization and its information needs. To accomplish this, the information structure must accurately define and characterize the items of data and the relations among them that are of interest to the users. This is no small task, for it demands a knowledge of the organization and the distribution of information among its various parts." (Robert W Taylor & Randall L Frank, "CODASYL Data-Base Management Systems", 1976)
"A variety of reasons make careful database design essential. These include data redundancy, application performance, data independence, data security, and ease of programming. All are important factors in the data processing environment, and all can be adversely affected by a poor database design." (Mark L Gillenson, "Database: Step by Step", 1985)
"Database design refers to the process of organizing the data fields needed by one or more applications into an organized structure. This structure must foster the required relationships among the fields while conforming to the physical constraints of the particular database management system in use. There are two parts to the process that people usually associate with the term 'database design'. One is 'logical database design' which has two components. The first involves organizing the data fields into nonredundant groupings based on the data relationships. The second involves an initial organizing of those logical groupings into structures based on the nature of the DBMS and of the applications that will use the data. […] The second part of database design is 'physical database design, which refers to refitting the previously described derived structures to conform to the performance and operational idiosyncrasies of the DBMS, again guided by the application's processing requirements." (Mark L Gillenson, "Database: Step by Step", 1985)
"The conceptual model is the focal point of the process of database design. All activities either converge upon or emanate from the conceptual model. All structures, through mappings either into or out of the conceptual model, must be to some extent compatible with it." (Andrew Pletch, "Conceptual Modeling in the Classroom", SIGMOD Record 18(1), 1989)
"Because one has to be an optimist to begin an ambitious project, it is not surprising that underestimation of completion time is the norm." (Fernando J Corbató, "On Building Systems That Will Fail", 1991)
"It is important to emphasize the value of simplicity and elegance, for complexity has a way of compounding difficulties and as we have seen, creating mistakes. My definition of elegance is the achievement of a given functionality with a minimum of mechanism and a maximum of clarity." (Fernando J Corbató, "On Building Systems That Will Fail", 1991)
"A database is basically a collection of related facts (e.g. a company's personnel records, or a bus timetable). Discovering the essential kinds of facts that underlie an application, and the conditions that apply to them, is both interesting and illuminating. The quality of the database design used for these facts and conditions is important. Just as a house built from a good architectural plan is more likely to be safe and convenient for living, a well-designed database simplifies the task of ensuring that its facts are correct and easy to get at." (Terry Halpin, "Conceptual Schema & Relational Database Design" 2nd Ed., 1995)
"If an application requires maintenance and retrieval of large amounts of data, a DBMS offers many advantages over manual record-keeping systems. Operations on data may often be performed faster. Data may be stored compactly on disk, and redundancy may be reduced by data sharing. Many data errors can be avoided by automatic integrity checking. With multi-user systems, access rights to data can be enforced by the system. People can spend more time on creative design rather than on routine tasks more suited to computers."(Terry Halpin, "Conceptual Schema & Relational Database Design" 2nd Ed., 1995)
"No matter how sophisticated the information system, if we give it the wrong picture of our UoD to start with, we can't expect to get much sense out of it. This is one aspect of the gigo (Garbage In Garbage Out) principle. Most of the problems with many database applications can be traced to bad database design." (Terry Halpin, "Conceptual Schema & Relational Database Design" 2nd Ed., 1995)
"When we design a database for a particular application, we create a model of it. Technically, the application area that we are modeling is called the universe of discourse (UoD), since it is the world (or universe) that we are interested in talking (or discoursing) about. Typically the UoD is a 'part' of the 'real world'. To build a good model requires a good understanding of the world we are modeling, and hence is a task ideally suited to people rather than machines. The main challenge is to describe the UoD clearly and precisely. Great care is required here, since errors introduced at this stage filter through to later stages in software development, and the later the errors are detected the more expensive they are to remove." (Terry Halpin, "Conceptual Schema & Relational Database Design" 2nd Ed., 1995)
"A bad logical design means that a good physical design cannot be performed. Good logical design is crucial to good database performance, and a bad logical design will result in a physical design that attempts to cover up the weaknesses in it. A bad logical design is hard to change, and once the system is implemented it will be almost impossible to do so." (Ken England, "Microsoft SQL Server 2000 Performance Optimization and Tuning Handbook", 2001)
"[…] physical database design is not a static, one-off process. Once the database has gone into production, the user requirements are likely to change. Even if they do not, the database data is likely to be volatile, and tables are likely to grow." (Ken England, "Microsoft SQL Server 2000 Performance Optimization and Tuning Handbook", 2001)
"The physical design process is a key phase in the overall design process. It is too often ignored until the last minute in the vain hope that performance will be satisfactory. Without a good physical design, performance is rarely satisfactory and throwing hardware at the problem is rarely completely effective. There is no substitute for a good physical design, and the time and effort spent in the physical design process will be rewarded with an efficient and well-tuned database, not to mention happy users!" (Ken England, "Microsoft SQL Server 2000 Performance Optimization and Tuning Handbook", 2001)
"There is no right way to design a database; there are a number of possible approaches and all these may be perfectly valid. It is sometimes said that performance tuning is an art, not a science. This may be true, but it is important to undertake performance tuning experiments with the same kind of rigorous, controlled conditions under which scientific experiments are performed." (Ken England, "Microsoft SQL Server 2000 Performance Optimization and Tuning Handbook", 2001)
"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)
No comments:
Post a Comment