Relation Variables

This chapter focuses on the logical difference between relation values (relations) and relation variables (relvars). In particular, it discusses and explains a variety of concepts and properties that are widely thought of as applying to relations as such but in fact don’t—they apply to relvars instead. The concepts in question include relational assignment (the well known shorthands INSERT, DELETE, and UPDATE in particular, also the less well known shorthands D_INSERT and I_DELETE); keys and foreign keys; key constraints, foreign key constraints, and other integrity constraints; The Golden Rule; and base vs. virtual relvars (views). The chapter concludes by defining and discussing the relational model as such.