tailieunhanh - Database Modeling & Design Fourth Edition- P13

Database Modeling & Design Fourth Edition- P13: Database technology has evolved rapidly in the three decades since the rise and eventual dominance of relational database systems. While many specialized database systems (object-oriented, spatial, multimedia, etc.) have found substantial user communities in the science and engineering fields, relational systems remain the dominant database technology for business enterprises. | Activity Diagrams 47 Nodes initial node final node activity node Control flow decision branch fork join Organization partition swim lanes Subset Name 1 Subset Name 2 Figure UML activity diagram constructs sion node must be mutually exclusive to avoid nondeterministic behavior. There can be no ambiguity as to which direction the control flows. The guards must cover all possible test conditions so that control is not blocked at the decision node. One path may be guarded with else . If a path is guarded by else then control flows in that direction only if all the other guards fail. Forks and joins are both forms of synchronization written with a solid bar. The fork has one incoming flow and multiple outgoing flows. When control flows to a fork the control concurrently 48 CHAPTER 3 The Unified Modeling Language UML follows all the outgoing flows. These are referred to as concurrent threads. Joins are the opposite of forks the join construct has multiple incoming flows and one outgoing flow. Control flows from a join only when control has reached the join from each of the incoming flows. Activity diagrams may be further organized using partitions also known as swim lanes. Partitions split activities into subsets organized by responsible party. Each subset is named and enclosed with lines. Activity Diagrams for Workflow Figure illustrates the UML activity diagram constructs used for the publication of this book. This diagram is partitioned into two subsets of activities organized by responsible party the left subset contains Customer activities and the right subset contains Manufacturer activities. Activity partitions are sometimes called swim lanes because of their typical appearance. Activity partitions may be arranged vertically horizontally or in a grid. Curved dividers may be used although this is atypical. Activity diagrams can also be written without a partition. The construct is organizational and doesn t carry inherent semantics. The meaning

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