What does the "extends"-relationship mean in conjunction with Profiles

[Viking]

Hi together,

We created an own profile with MDG. Unfortunately I do not understand the concept behind "Extension" resp. "extends". What does "extends" mean in conjunction with metaclasses (resp. a stereotype extends Metaclass) resp. what effects would "extends" have on software, for example? I only know and understand "extends" in conjunction with UseCases.

Many thanks in advance, V.

[Uffe]

Hello,


There is no meaningful parallel between the metaclass extension relationship and the use case extends relationship. They mean different things and are from completely different contexts.

The extension relationship from a stereotype element to a metaclass element, in EA's profile models, means that the stereotype will apply to the metaclass. Another way of putting it is that you are creating a subtype of the metaclass.

The subtype can be used in any context where UML (and EA) allows the metaclass, but you can also add additional semantics that apply only to the subtype. For instance, you can specify additional properties for elements of the subtype (tagged values), and you can place restrictions on what types of connectors can be drawn to/from them.

As to the effect of "extends" on software, this question makes no sense. Software is not an element type in UML. You can define one in your own metamodel, and define an "extends" relationship between such elements, but it is then up to you the metamodeller to specify the semantics of that relationship.

HTH,


/Uffe

[Viking]

Thank you, Uffe.

I did not want to use the concept for software development. I just thought there where an analogy in software development to better understand the concept.

[Geert Bellekens]

The profile "extends" is more like the "inherits", or "specializes" relation (technically the UML Generalization) known in class models.

Geert