Re: Join constraints

Jernej Kase wrote:
>How can one set external constraints over join path using visio orm
>source diagram?
>
>For example, let's say we have three objects:
> Owner (ownID)
> Building (buildID)
> Room (roomID)
>
>And fact types:
> Owner is owner of zero or more Building / Building is owned by zero
>or one Owner.
> Owner is owner of zero or more Room / Room is owned by zero or one
>Owner.
> Room belongs to exactly one Building.
>
>I would like to set the following constraint:
> Building b is owned by Owner xor Room r is owned by Owner, Room r
>belongs to Building b.
>
>Is there a way to describe this constraint?

Not in ORM (or FORML as they now call it) as it is now. It's the best data model around but somehow these ORM guys and girls still don't realize that all these cute graphical constraints are sometimes not enough and you need a serious constraint languages based on something like first-order (or higher-order) logic for those cases. Such a thing is very easy to design, but they didn't, so there you go.

• Jan Hidders