Primary Keys as Indices
Let integer coordinates i = pk(xi) and j = pk(yj) index the elements of X and Y, and redefine CFR(x,y) as CFK(i,j) in {TRUE, FALSE}.
Then members of R(x, y) correspond 1 to 1 with integer pairs or 2-D points where CFK(i,j) = 1.
If x and y are two entity or record types in a database, the integer variables i and j play the role of primary keys on the Domain and CoDomain.
- Ref: 96f523 project on binary Join extension of chgen.
- Question: What if the relation is ternary (N=3)?
Relations may represent a participating entity instance by reference, as a foreign key or fkey, whose value matches the pkey of the referenced object.