Re: modeling either/or relationship...

"Volker Hetzer" <volker.hetzer_at_ieee.org> wrote in message news:drd0q3$idc$1_at_nntp.fujitsu-siemens.com...
> Hi!
> I've got to model electrical constraints on a net of a pcb.
> So, a net can be constrained either by layer,net class (and constraint
name)
> or constraint class (and constraint name).
>
> The problem I have is that a constraint (with a name and a bunch of
attributes)
> can be either
> - a "free constraint, adressed by layer, net class and name or
> - a "bound constraint", adressed by the constraint class name.
> A constraint cannot be both.
>
> I can enforce this easily with a table constraint (id set1 xor id set2 is
true), but
> can I put this into an ER diagram too?
>
> Lots of Greetings!
> Volker

Look up "generalization specialization relational model" on the web. Received on Fri Jan 27 2006 - 13:37:00 CET