Re: A real world example

JOG wrote:
> Originally Codd used the terms "roles and values" in the
> 1970 paper. Perhaps the commonm use of 'attributes and values' to
> describe a relation encourages the "thing-oriented" approach.

Probably true - on its own, the word "attribute" implies a thing (noun) its value is attributed to.

I try to remember Date's loose analogy of predicates as sentences, and attributes as nouns in the sentence. A predicate is a type of statement; each tuple is a specific statement about specific values, a statement we assert is true (and Closed World means those not in the database are assumed false). Constraints, then, are our means of keeping statements consistent in meaning, since the DBMS can't know the real-world meaning of any of them.

I'm not sure "roles and values" is any better; "predicates and free variables," or "predicates and terms," while less intuitive, are as close as I can get.

• erk