Re: Relation Schemata vs. Relation Variables


Brian Selzer wrote:

[...] A delete/insert combination would have to
satisfy any delete constraints or insert constraints or both, but that
doesn't mean that the update constraint couldn't still be circumvented.

Indeed, but the point is not whether they can be circumvented or not
because in both aprroaches (your approach and a relational assignment
approach) you can circumvent it. However under the relational
assignment approach one combines inserts and deletes into a single
assignment which would be checked as a whole, so there would at least
be less opportunity to get around it. Of course the tighter control
comes at a price: explicit modelling of an entity-pairing rule in the
transition constraint. But given that making such a thing explicit is
probably not unwise anyway and that it is more faithful to the
"database is a set of propositions" paradigma, I'd say it is the better
option.

-- Jan Hidders

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