The activity diagram
Describing a flow with an activity diagram: actions, initial and final nodes, decision and merge with guards, fork and join, swimlanes per actor.
- 26 cards
- 3 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- Concepts
- Questions
- Sort and link
A few cards from the deck
Activity diagram: what is it?
Show the answer
A UML diagram that describes a sequence of actions, with its choices and its steps run in parallel, from the start to the end of a process.
It suits a use case, a business process or an algorithm. The arrows carry the flow of control from one action to the next.
A fork starts “prepare the parcel” and “issue the invoice”. When does the flow pass the join that closes them?
- When both actions are finished
- As soon as the first of the two is finished
- As soon as one of the two guards is true
- After one of the two branches has been chosen
Show the answer
When both actions are finished
The join synchronises: it waits for all branches. A guard or a choice of branch belongs to the decision, not to parallelism.
A decision picks … branch according to a guard; a fork starts … of its branches in parallel.
Show the answer
A decision picks a single branch according to a guard; a fork starts all of its branches in parallel.
This is the most common confusion between the two notations: the diamond chooses, the thick bar parallelises.
Decision node: what is it?
Show the answer
A diamond with one input and several outputs, of which only one is followed depending on the condition written on each outgoing arrow.
The conditions in square brackets must exclude each other and cover every case:
[payment accepted]and[else].Two branches coming out of a decision meet before “Archive the order”. Which node goes at the meeting point?
- A join
- A merge
- A fork
- A final node
Show the answer
A merge
Only one of the two branches was followed. A join would wait for the other one forever and the process would stay stuck; the merge lets the arrived branch through.