SQL and Relational Theory, 2nd Edition

CONCLUDING REMARKS

This brings us to the end of this preliminary chapter. For the most part, my aim has just been to tell you what I rather hope you knew already (and you might have felt the chapter was a little light on technical substance, therefore). Anyway, just to review briefly:

• I explained why we’d be concerned with principles, not products, and why I’d be using formal terminology such as relation, tuple, and attribute (at least in relational contexts) in place of their more “user friendly” SQL counterparts.

• I gave an overview of the original model, touching in particular on the following concepts: type (or domain), n-ary relation, tuple, attribute, candidate key (key for short), primary key, foreign key, entity integrity, referential integrity, relational assignment, and the relational algebra. (I also briefly mentioned the relational calculus.) With regard to the algebra, I mentioned the closure property and very briefly described the operators restrict, project, product, intersection, union, difference, and join.

• I discussed various properties of relations, introducing the terms heading, body, cardinality, and degree. Relations have no duplicate tuples, no top to bottom tuple ordering, and no left to right attribute ordering. I also discussed the difference between base relations (or base relvars, rather) and views. And I explained that every subset of a tuple is a tuple, every subset of a heading is a heading, and every subset of a body is a body.

• I discussed the logical ...