It is very important to distinguish between the UML model and the set of diagrams of a system. A diagram is a partial graphical representation of a system’s model. The model also contains a “semantic backplane” — documentation such as written use cases that drive the model elements and diagrams.There are four parts to the UML 2.x specification: the Superstructure that defines the notation and semantics for diagrams and their model elements; the Infrastructure that defines the core metamodel on which the Superstructure is based.UML does not restrict UML element types to a certain diagram type. In general, every UML element may appear on almost all types of diagrams. This flexibility has been partially restricted in UML 2.0.

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Class diagrams are the backbone of almost every object oriented method, including UML. They describe the static structure of a system.Package diagrams are a subset of class diagrams, but developers sometimes treat them as a separate technique. Package diagrams organize elements of a system into related groups to minimize dependencies between packages.

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This third edition of dbDesign is a general update, both to meet legal requirements for U.S. “Section 508” accessibility and to bring the code into compliance with the latest World Wide Web Consortium standards. In the process, I’ve tried to make the SQL examples as generic as possible, although you will still have to consult the documentation for your own database system. Graphics no longer require the SVG plugin; large-image and text-only views of each graphic are provided for all readers; the menu is now arranged by topic areas; and the print version (minus left-side navigation) is done automatically by a style sheet.

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