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Editorial Team
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Asked: 2026-05-20T20:47:06+00:00

Is it valid to have an Interface as part of a sequence diagram. For

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Is it valid to have an Interface as part of a sequence diagram. For instance, is the following UML valid? The purpose of the interfaces is to show extensibility and testability points in the design. You could extend by providing a different implementation for each interface and better test by replacing the interfaces with mocks. However, I don’t know if this violates the rules of UML. Thanks in advance.

GameService:IGameService     GameRepository:IGameRepository
           |                            |
           |                            | 
           |--------------------------->|
           |                            |
           |                            |
           |                            |

P.S.: Sorry for the poor’s man diagram.

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1 Answer

  1. Editorial Team

    Of course a lifeline in a sequence diagram can represent an (instance of an) interface. From the perspective of the diagram, it doesn’t matter much—there are no restrictions on where the operations/messages on the events should come from.
    If you want to indicate that the operations have to come e.g. from the signature of the target (IGameRepository), you have to document/encode this separately, e.g. in OCL.

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