18 Questions
What is represented by a note in an activity diagram in UML?
Annotation
How are notes attached to the model elements in activity diagrams?
Dashed line
What is represented by a pair of square brackets in an activity diagram?
Guard condition
What does a merge node do in an activity diagram?
Allows multiple flows to join together
How is the flow between activities constrained in UML activity diagrams?
Guards
How is concurrency achieved in activity diagrams?
Synchronization bars
What is the central process involved in making a hot drink?
Boiling water in a kettle
In an activity diagram, how are activities typically represented?
Rounded boxes
What do completed activities trigger in an activity diagram?
Outgoing transitions
Which symbol represents a decision point in an activity diagram?
Diamond
What do start and stop nodes represent in an activity diagram?
Filled circles
Which element in an activity diagram denotes a fork?
Thick horizontal line
What is the purpose of redrawing the activity diagram in Example 3?
To allow the choice between coffee with milk and coffee without milk
In Example 4, what new choice is introduced in the activity diagram for preparing a pot of tea?
Choice of milk and sugar
What is expected of a library member in the borrowing process according to the text?
Return the books that they have on loan after a certain period
What action does the librarian take if a member fails to bring a borrowed book back on time?
Imposes a fine
What does the possession of a book during the loan period signify?
The book is temporarily owned by the borrowing member
What happens if a library member waits in line but then decides not to borrow any book?
The librarian records a return instead of a loan
Study Notes
Activity Diagrams
- An activity diagram is a type of UML diagram that shows the flow of activities and decisions in a system.
Elements and Symbols
- Activities are shown as rounded boxes.
- Transitions are shown as lines with arrows.
- Start and stop nodes are represented as filled circles.
- Synchronization bars are denoted by thick horizontal lines and used to show concurrent activities.
Notes and Annotations
- A note (with annotation) is shown as a rectangle with the top right-hand corner folded down.
- A dashed line is used to attach the note to the model element to which it refers.
Decision and Merge Nodes
- A diamond shape is used as a decision node, which represents a Boolean test (guard) that determines which path to take.
- One outgoing transition from a decision node should always be taken, meaning exactly one of the relevant guards must always evaluate to true.
- A diamond shape is also used as a merge node, which brings together alternative mutually exclusive flows.
Workflow and Activities
- Workflow is defined as a sequence of activities that produces a result of observable value.
- An activity has only one transition into and out of it, which is enforced by decision and merge nodes for alternative outgoing and incoming transitions, and by synchronization bars for concurrent outgoing (fork) and incoming (join) transitions.
Examples of Activity Diagrams
- Preparing a cup of coffee, with the ability to check if the cup is clean and wash it if necessary.
- Preparing a cup of coffee, with the choice of coffee with milk or coffee without milk.
- Preparing a pot of tea, with the choice of milk and sugar when the tea is poured.
- The lending process from a library, including borrowing and returning books.
Test your knowledge on UML activity diagrams and notes. Practice redrawing activity diagrams with specific examples like preparing a cup of coffee and checking if the cup is clean.
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