Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

"Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message news:I4Cxe.135796$Bh7.7066690_at_phobos.telenet-ops.be...
> Jon Heggland wrote:

[...]
>> Not personally, but what more do you need than definitions of value,
>> domain, tuple and relation, and a minimal set of algebra operators?
>
> The notions of database schema, database constraints, database instances
> and how they are exactly related.

A constraint (in the RM) is just a predicate [required to evaluate to true].

A relation schema is a schema name R and a set of attributes A: R(A)

A database schema is a pair (RR, C) where RR is a set of relation schemata and C is a set of constraints on RR.

A relation instance for R(A) is a set of tuples.

>
> -- Jan Hidders
Received on Sun Jul 03 2005 - 08:29:20 CDT