CODEWITHSUNDEEP
umlsequence-diagram
sc0ttman
sc0ttman

Reputation: 69

How to represent Actor generalization/specialization in a UML Sequence Diagram?

I have a use case diagram, which has three Actors: User, Librarian and Staff.

The Staff and Librarian actors are specializations of the User actor, and in the Use Case diagram they each have some extended use cases associated only to them.

  1. In the sequence diagram, how do I show that the Librarian actor is a specialization of the User actor?

  2. Can the specialized actors (Librarian and Staff) have their own timelines in the Sequence diagram?

  3. Do I have to show a timeline for the generalized actor, even if it has no extra uses cases or actions over its specializations?

  4. Is it OK to re-arrange the Timelines of a sequence diagram once it has been extracted out into its own diagram, using an Interaction Use box in the main sequence diagram?

Upvotes: 1

Views: 2045

Answers (1)

xmojmr
xmojmr

Reputation: 8145

  1. In the sequence diagram, how do I show that the Librarian actor is a specialization of the User actor?

There's no way (as far as I know). You can show this relationship in UML Use Case Diagram and even better in UML Class Diagram

  1. Can the specialized actors (Librarian and Staff) have their own timelines in the Sequence diagram?

Yes, assuming they both play a role and interact in the scenario which the Sequence Diagram captures

  1. Do I have to show a timeline for the generalized actor, even if it has no extra uses cases or actions over its specializations?

No, you don't have to show formally correct but otherwise useless artifacts in your diagrams, unless a followup code generation (or MDA) tool forces you to do so

  1. Is it OK to re-arrange the Timelines of a sequence diagram once it has been extracted out into its own diagram, using an Interaction Use box in the main sequence diagram?

I'm not sure, but probably yes, if you keep binding of inputs and outputs and information identifying the lifeline clear and valid. Some articles where the correct answer might be hidden:

  • Source: uml-diagrams.org: UML Sequence Diagrams → Interaction Use

    ...One constraint imposed by UML specification that is sometimes difficult to follow is that the interaction use must cover all involved lifelines represented on the enclosing interaction. This means that all those lifelines should be somehow located near each other. If we have another interaction use on the same diagram it could be very tricky to rearrange all involved lifelines as required by UML

  • Source: www.omg.org/spec/UML/2.5/Beta2

    17.7 Interaction Uses → Semantics → Part Decompositions

    Decomposition of a lifeline within one Interaction by an Interaction (owned by the type of the Lifeline’s associated ConnectableElement), is interpreted exactly as an InteractionUse. The messages that go into (or go out from) the decomposed lifeline are interpreted as actual gates that are matched by corresponding formal gates on the decomposition.

    As the decomposed Lifeline is interpreted as an InteractionUse, the semantics of a PartDecomposition is the semantics of the Interaction referenced by the decomposition where the gates and parameters have been matched...

    17.7 Interaction Uses → Notation → PartDecomposition

    PartDecomposition is designated by a referencing clause in the head of the Lifeline as can be seen in the notation sub clause 17.3.4 (Lifeline) (see also Figure 17.21).

    If the part decomposition is denoted inline under the decomposed lifeline and the decomposition clause is “strict,” this indicates that the constructs on all sub lifelines within the inline decomposition are ordered in strict sequence (see 17.6.4 (Strict interactionOperator)...

    enter image description here Figure 17.21 PartDecomposition - the decomposed part

    ...

Upvotes: 1

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