If and how to represent ordered / unordered containments in M3

[enikao]

We support multi-valued Containments in M3.
In our first online meeting (#2), we discussed whether to qualify the kind of their sequence.

Proposals included:

• Flag ordered vs. unordered
• Flag sortable

Aspects:

• When creating domain models, it's mostly convenient to have ordered containments.
• For automatic merging / diffing, explicitly knowing the order doesn't matter is very useful
• Collaborative modeling / distributed data structures can handle unordered collections a lot easier.

[markusvoelter]

So I guess we'll have them? I don't see con-arguments?

[dslmeinte]

Insertion order by default, unordered or ordered in a particular way through annotations?

[ftomassetti]

+1 for having unordered as an annotation

[joswarmer]

I'd say that we need at least ordered, as the order may carry semantics. E.g. if I have in my language a Statement list containing many Statements, these have to be ordered.

[joswarmer]

Also, for users editing models, it is very inconvenient, if not completely unworkable, if the order of elements has changed after saving and retrieving a model.