“■ Types are (sets of) things we can talk about.
■ Relations are (sets of) things we say about the things we can talk about.

(There is a nice analogy here that might help you appreciate and remember these important points: Types are to relations as nouns are to sentences.) Thus, in the example, the things we can talk about are employee numbers, names, department numbers, and money values, and the things we say are true utterances of the form “The employee with the specified employee number has the specified name, works in the specified department, and earns the specified salary.”

It follows from all of the foregoing that:
1. Types and relations are both necessary (without types, we have nothing to talk about; without relations, we cannot say anything).
2. Types and relations are sufficient, as well as necessary—i.e., we do not need anything else, logically speaking.
3. Types and relations are not the same thing. It is an unfortunate fact that certain commercial products—not relational ones, by definition!—are confused over this very point.”