Model composition where instance of class is used multiple times

Question

I want to model the following scenario:

• A message a consists of one or more base types.
• Base types are uint8 .. uint64 and int8 .. int64.
• A message can also contain other messages.

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Example:

Message position

• uint8 x
• uint8 y

Message movement

• position start
• position end
• uint8 speed

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This is what i modeled in Sirius so far

The issue here is that I cannot link the message position twice to the message movement. Can you please provide a approach of modelling this problem?

Answer 1

Your modelization is lacking one "layer" to represent your "message type" / "message instance" structure.

I think what you need to do is something a bit like this:

• Class MessageType with a containment towards BaseType (which IMO should be renamed something like MessageDataType)
• Class MessageInstance with a containment towards itself and a reference to a MessageType.

Then you end user must first create a MessageType instance, called "position" and a second one called "movement". Then create three MessageInstance instances, two pointing towards MessageType "movement" and one containing the first two MessageInstance instances.

I would also advise seriously thinking about how you want to name your concepts, because there is a potential confusion between an Ecore instance of one of your EClass and the fact that you are effectively modeling a type/instance structure.