Re: Another view on analysis and ER


"paul c" <toledobythesea@xxxxxxxx> wrote in message
news:JBD6j.5404$jq2.1804@xxxxxxxxxxxx
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.



.

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