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The above diagram shows a system - the construction supply process - represented as a composition of component systems. The three rectangles in the middle represent the roles of "buyer", "site manager" and "accounts clerk" in a construction company, the two on the left the roles of the "sales persons" and "delivery persons" in the suppliers of that construction company, and the one on the right the role of "engineer" in the customer of the construction company. The engineer may choose some of the suppliers used by the construction company. Otherwise the construction company picks its suppliers by reference to directories of suppliers (maintained by "directory agencies"). The lines between rectangles represent flows of information and artifacts between the roles represented by the rectangles.
Note that some of the rectangles and lines in the diagram (such as "supplier sales persons" and "orders") represent sets of similar components whilst others (such as "site manager") represent single components. This problem is addressed by the definition of POSD but need not concern the reader here.
last revision: 21st June 1997