3 - The Unified Modeling Language

Abstract

The Unified Modeling Language (UML) is a graphical language for communicating design specifications for software, currently very popular for communicating design specifications for software and, in particular, for logical database designs via class diagrams. The object-oriented software development community created UML to meet the special needs of describing object-oriented software design. UML has grown into a standard for the design of digital systems in general. The similarity between UML and the entity–relationship (ER) model is shown through some common examples in this chapter, including ternary relationships and generalization. UML activity diagrams are used to specify the activities and flow of control in processes. There are a number of different types of UML diagrams serving various purposes. The class and the activity diagram types are particularly useful for discussing database design issues. UML class diagrams capture the structural aspects found in database schemas. UML activity diagrams facilitate discussion on the dynamic processes involved in database design. This chapter is an overview of the syntax and semantics of the UML class and activity diagram constructs used in this book. These same concepts are useful for planning, documenting, discussing and implementing databases. UML activity diagrams are similar in purpose to flow charts. Processes are partitioned into constituent activities along with control flow specifications. This chapter is organized into three main sections. The first section presents class diagram notation, along with examples. The next section covers activity diagram notation, along with illustrative examples. Finally, the last section concludes with a few tips for UML usage.