Activity diagram
The notation of the UML activity diagram: initial and final nodes, actions, decision and merge with guards, fork and join, swimlanes.
- 21 cards
- 4 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
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A few cards from the deck
Action: what is it?
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An elementary step of the flow, drawn as a rounded rectangle: it finishes, then hands over to the next one.
It is named with a verb (“Check the stock”) and drawn with a single exit: to choose a path or start several, you go through a decision or a fork.
After “Pay”, the parcel is packed while the invoice is issued, and shipping waits for both. Which nodes go before and after those two actions?
- A fork, then a join
- A decision, then a merge
- A join, then a fork
- A decision, then a join
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A fork, then a join
Both actions must happen: a fork to start them, a join to wait for them. A decision would send only one path; with a join behind it, the diagram would get stuck.
The flow starts at the … node, a filled disc, and ends at the … node, a filled disc inside a circle.
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The flow starts at the initial node, a filled disc, and ends at the final node, a filled disc inside a circle.
You usually start from a single initial node, and you may place several final nodes. The first activity final node reached stops every path still running.
Guard: what is it?
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A condition in square brackets carried by a branch, like
[in stock]: it must be true for the path to be taken.The guards on a decision's exits must exclude each other and cover every case;
[else]is the last resort.Why does a join placed right after a decision block the diagram?
- It can only be used inside a single swimlane
- It rejects any incoming branch that carries a guard
- It waits for every incoming path; the decision takes only one
- It runs the two entries one after the other without waiting
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It waits for every incoming path; the decision takes only one
A join only releases when all incoming paths have arrived. After a decision, only one does: a merge is what brings them together.