A database design methodology is defined for the design of large relational databases. First, the data requirements are conceptualized using an extended entity-relationship model, with the extensions being additional semantics such as ternary relationships, optional relationships, and the generalization abstraction. The extended entityrelationship model is then decomposed according to a set of basic entity-relationship constructs, and these are transformed into candidate relations. A set of basic transformations has been developed for the three types of relations: entity relations, extended entity relations, and relationship relations. Candidate relations are further analyzed and modified to attain the highest degree of normalization desired. The methodology produces database designs that are not only accurate representations of reality, but flexible enough to accommodate future processing requirements. It also reduces the number of data dependencies that must be analyzed, using the extended ER model conceptualization, and maintains data integrity through normalization. This approach can be implemented manually or in a simple software package as long as a "good" solution is acceptable and absolute optimality is not required.
Database management systems have evolved to the point of general acceptance and wide application; however a major problem still facmg the user is the effective utihzatlon of these systems. Important to achmving effective database usability and responsiveness is the design of the database. This paper presents a practmal stepwlse database design methodology that derives a DBMS-processable database structure from a set of user information and processing requirements Although the methodology emphasizes the logical design step, the activities of reqmrements analysis and physmal design are also addressed. The methodology is illustrated wtth a detailed example Performance trade-offs among multiple users of a single integrated database are considered, and the relationship between short-term design and design for flexibility to changing reqmrements IS discussed.Many steps m the database design process can be assisted with proper use of computer modehng techniques and other tools, such as requirements analysis software. The example design problem and its solution steps serve to point out when and where current technology can be effectively used
The development of a powerful restructuring function involves two important components-the unambiguous specification of the restructuring operations and the realization of these operations in a software system. This paper is directed to the first component in the belief that a precise specification will provide a firm foundation for the development of restructuring algorithms and, subsequently, their implementation. The paper completely defines the semantics of the restructuring of tree structured databases.The delineation of the restructuring function is accomplished by formulating three different levels of abstraction, with each level of abstraction representing successively more detailed semantics of the function.At the first level of abstraction, the schema modification, three types are identified-naming, combining, and relating; these three types are further divided into eight schema operations. The second level of abstraction, the instance operations, constitutes the transformations on the data instances; they are divided into group operations such as replication, factoring, union, etc., and group relation operations such as collapsing, refinement, fusion, etc. The final level, the item value operations, includes the actual item operations, such as copy value, delete value, or create a null value.
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