Are interfaces allowed in UML sequence diagrams

Question

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.

Answer 1

Yes, this is possible. Both classes and interfaces are subclasses of Classifier in the UML metamodel. Classifiers are the ones linked to the elements in the sequence diagram