Re: foreign key constraint versus referential integrity constraint

Mr. Scott wrote:

>[...] Constraints specify what can and cannot be
>assigned a positive truth value, they do not specify what has been assigned
>a positive truth value. Queries manipulate what has been assigned a
>positive truth value or what can be derived from what has been assigned a
>positive truth value.

[Quoted] Formally: a database instance is a set of named relations, i.e. a mapping from names to relations.
A database is a set of possible database instances, such that each instance maps the same names to relations with, per name, the same signature. It is defined by a database schema (which maps each relation name to its signature) and database constraints (which limit the possible combinations of relations to which the names are mapped). (I can go on and define 'signature', etc.) A database constraint is a predicate on database instances.

A 'table' (in this context) is a named relation in a database instance, or perhaps a database restricted to that name (i.e. a relation name mapped to the set of all possible values for that relation).

A 'view' (in this context) is a named mapping from database instances to relations.

-- 
Reinier