Re: WWW/Internet 2009: 2nd CFP until 21 September
Date: Fri, 14 Aug 2009 19:39:50 GMT
Mr. Scott wrote:
> I think you're confused about what a predicate is. The predicate states the
> fact that an order has one address from the domain of all addresses.
> Whether that address is at present known or unknown doesn't change that
> fact. ...
I don't think so, in RT a predicate 'states' no fact until its variables are instantiated by the terms/values of a proposition/tuple, (aka extension) this results in a true or false propositon. In RT, only propositions can represent true or false facts. Predicates are not facts in Codd's model.
Maybe it's somehow different in SQL. One problem I have with SQL is that it seems extraordinarily unwieldy for defining constraints coherently, whereas in RA that's usually quite concise and it's clear what any invented shorthands really mean. Received on Fri Aug 14 2009 - 14:39:50 CDT