[vo-dml] Clarification on composition rule..

[CresitelloDittmar, Mark]

Hi,

In the Transform model, we have a case where we want to use the same Object
with different roles in the parent Object.
Specifically, we want to define a "Mapping" with a forward and inverse
"Operation".

What I'd like to do is:
[image: A.png]

But the VO-DML rec states; Section 4.17, pg 48, "an ObjectType can only be
the target of at most one Composition relation".
And this does indeed fail vo-dml validation.   NOTE: the nature of several
operations require it to be an ObjectType rather than a DataType, so these
can't be Attributes.

I CAN do:
[image: B.png]

Which has only 1 composition, but is hacky and not very user-friendly.. I'd
really prefer to have explicit 'forward' and 'inverse' tags.
To make a vo-dml compliant version of the first diagram, I need to add a
layer to the model.  This works fine, and is the current model, but is
rather ugly and makes it a little more difficult to interpret.

[image: C.png]

Mainly, I think I'm looking to confirm that the rule in Section 4.17 is
*intended* to include this case.
I expect it is, and has to do with RDB implementations and distinguishing
the instances, but I'm not a DB person and don't fully get all that.

Mark
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