[vo-dml] Clarification on composition rule..

[Patrick Dowler]

I don't understand "NOTE: the nature of several operations require it to be
an ObjectType rather than a DataType, so these can't be Attributes."

I have created models with DataType(s) that are "structures" so I could use
them as attributes in multiple places and I have declared DataType(s) that
extend (subclass) other DataType(s). Both of those are vodml compliant...
what is it that requires TOperation to be an ObjectType? Is it a
philosophical issue?

--
Patrick Dowler
Canadian Astronomy Data Centre
Victoria, BC, Canada


On Wed, 4 Mar 2020 at 09:43, CresitelloDittmar, Mark <
mdittmar at cfa.harvard.edu> wrote:

> 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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