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One Model, Many Interests, Many Views
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.