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Mapping for the Sequence Diagram

The interacting blocks involved in a function’s decomposition are displayed at the top of the diagram. Lifelines are shown as a dashed line extending downward from each interacting block. Individual function nodes in the decomposition are placed along the corresponding vertical lifeline (depending upon their allocation) in the sequence in which those functions occur. Often, these function nodes are unlabeled to focus attention on the interaction between the blocks. Control constructs (termed “interaction operators” in the language of the sequence diagram) are displayed in a lightweight manner and enclose the nested functions and constructs. This representation is much less complete than the control representation on an activity diagram or enhanced function flow block diagram, but it conveys essential nesting.

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