Validating a Relation Instance
It must be possible to recognize whether a candidate N-tuple is a legal value of some particular N-ary relation.
This set of legal values may be enumerated as a set of points and/or intervals, computed by an algorithm, or tested for membership by a logical predicate based on a set of rules.
Examples:
- The relation from an offered Course to its (set of) Pre-requisite Courses is a tabulated multi-valued function.
- The Father to Son relation between two Persons must obey the constraint Sex=‘Male’ on any Person having the role of Father or Son.
- The relation isLengthOf(h, Vector(x, y)) must satisfy the Pythagorean Theorem (h2 = x2 + y2).