In this appendix, a top-down approach to database design is illustrated. In this approach the following topics are discussed:
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Identifying the real-world entities that are involved. These entities typically correspond to (disjoint) Enterprise Database Server data sets.
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Using a notation to represent the relationships between the data sets.
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Developing techniques for mapping the relationships between data sets in disjoint data sets and index sequential sets, for one-to-one (1-to-1), one-to-many (1-to-N), and many-to-many (M-to-N) relationships.
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Using different programming techniques for handling the relationships simply and efficiently.
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Illustrating how data items are often added as the design progresses in a series of successive refinements.
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Refining the concepts behind the data sets to eliminate update anomalies.
Using the information in this appendix, you can design a database that is simple, easy to comprehend, general, extendible, and easy and efficient to interrogate and update. Normally, the final DASDL description consists of primarily disjoint standard data sets, index sequential sets, and automatic subsets, with relatively few links, embedded structures, or manual sets. Use of the later structures can make the database unnecessarily complicated, overly constrained, inflexible, and less efficient instead of more sophisticated. In contrast, use of disjoint structures can help make the database simple, efficient, and easily recoverable.
