[talaketu]

Exactly. Primary key is a subset of attributes - thus necessarily populated by values.

It's worth considering the correspondence between the concept of functional dependency in the relational model, and the concept of a pure function in functional programming. The issue under discussion, then, is whether referential transparency is afforded in the database.

While referential transparency in a database is achieved momentarily at the right isolation level, it is not achieved in the eternal sense of a pure function.

This is because the functional dependency in FP encodes an intensional definition, whereas the functional dependency captured in a relation is extensional, usually modelling the state of the knowledge of the relevant world, and therefore being subject to change.