A data model is a representation of the information consumed and produced by a system, which lets you analyze the data objects present in the system and the relationships between them. PowerDesigner® provides conceptual, logical, and physical data models to allow you to analyze and model your system at all levels of abstraction.
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Joe Celko, Joe Celko's SQL for Smarties (Morgan Kaufmann Publishers, Inc., 1995), 467 pages; paperbound; ISBN 1-55860-323-9.