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Concurrent Activities in Activity Diagrams

publish date: 2026/06/08 03:53:21.873125 UTC

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In the involuntary patient detention activity diagram, after the patient is transferred to a secure hospital, three activities can happen concurrently: informing social care, informing the next of kin, and updating the detention register. What UML notation element signals that these activities may be executed in parallel?

Guard conditions in square brackets on each arrow

Three separate start nodes, one for each concurrent activity

A diamond shape splitting the flow into three branches

A solid bar from which multiple arrows lead to the concurrent activities

Correct Answer

A solid bar from which multiple arrows lead to the concurrent activities

Explanation

When the flow from a solid bar leads to a number of activities, those activities may be executed in parallel. This is the fork notation in UML activity diagrams — a single solid bar fans out into multiple outgoing arrows, each pointing to an activity that can run concurrently. A diamond is used for mutually exclusive alternatives, not parallel execution.

Reference

Software Engineering, Ian Sommerville, 9th edition

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