Which node marks the start of concurrent sequences in an activity?

Which node marks the start of concurrent sequences in an activity?

• A. Fork node
• B. Join node
• C. Decision node
• D. Merge node

Answer: (A)

In activity diagrams, parallel execution starts when the flow is split into multiple paths. A fork node does exactly this: it takes one incoming flow and creates several outgoing flows that can run concurrently. This is how concurrent sequences begin. By contrast, a join node waits for all parallel paths to complete and then merges them back into a single flow, signaling the end of that concurrent section. A decision node selects one path based on conditions, and a merge node simply combines multiple alternative paths into one without starting parallelism. So the fork node is the element that marks the start of concurrent sequences.

In activity diagrams, parallel execution starts when the flow is split into multiple paths. A fork node does exactly this: it takes one incoming flow and creates several outgoing flows that can run concurrently. This is how concurrent sequences begin. By contrast, a join node waits for all parallel paths to complete and then merges them back into a single flow, signaling the end of that concurrent section. A decision node selects one path based on conditions, and a merge node simply combines multiple alternative paths into one without starting parallelism. So the fork node is the element that marks the start of concurrent sequences.