Re: Another view on analysis and ER

From: Brian Selzer <>
Date: Sun, 09 Dec 2007 13:52:48 GMT
Message-ID: <QqS6j.69545$>

"paul c" <> wrote in message news:JBD6j.5404$jq2.1804_at_pd7urf1no...
> JOG wrote:
> ...
>> 1) Married(Husband:John, Wife:Jane, Instituion:Church)
>> 2) EXISTS! x E marriages [ Husband(x, John) ^ Wife(x, Jane) ^
>> Institution(x, Church) ]
>> First one is marriage as a predicate, the second one the marriage as a
>> thing, x. Which to choose, and when. And if it depends ona certain
>> application, does picking one not bind us into that single conceptual
>> model?
>> ...
> PMFJI, just like to point out that when either hits the machine, the
> variables husband, wife, institution are the same, one of Codd's central
> points I think.
> Giving the relation a name is just a convenience and possibly an
> ill-considered choice to expand the name space of the possible types of
> relations in the db, eg., allow two relations with the same
> variables/attributes.

I don't think so. The names are not just a convenience, nor is the choice ill-considered. Under a FOL interpretation, each predicate symbol is assigned a distinct meaning. The name of a relation schema corresponds to that FOL predicate symbol. And it is not always the case that every relation schema in a database will have a different set of attributes, nor should it be. Received on Sun Dec 09 2007 - 14:52:48 CET

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