(1) A statement with one or more arguments implying a
constraint among cooccurring values of these arguments. E.g., a mathematical
function such as the
logarithm, an ordering such as "is greater than" or "causes", a statement of association such as "is married to", a correspondence, a
code. Equivalently (2), a subset of elements of a
cartesian product set (Wiener). When that subset contains observed or permissible cooccurrences, its complement in the same product set is called a
constraint and contains conceivable cooccurrances that did not occur or are excluded. Relations are of different
ordinality. Unary relations or properties are of order one.
binary relations are of order two, etc. Relations may be combined to form new relations, e.g., the simple ternary relation of "off-spring" which relates a father, a mother and a child can be used recursively (
see recursion ) to generate a whole family tree. More than one relation may be defined in the same Cartesian product set as the relations "talked to", "is married to", "exchanged goods with" all of which are subsets of the product of two sets of people. (
Krippendorff )
