In article <PuCNf.675$ZL1.646_at_trndny09>, dcressey_at_verizon.net says...
> If you have set types and tuple types, do you need to define relations
> separately as a type? Can't you merely define a relation as a set of
> tuples?
Possibly; I think that is mainly a matter of perspective. A relation is
constrained to contain tuples of just one tuple type. If we have a set
type generator (think the generic Set of Java 5) that can enforce this,
it might fit the bill. However, there are at least two issues:
- An empty relation of one type should not be equal to an empty relation
of another type. In Java, all empty sets are equal:
new HashSet<String>().equals(new HashSet<Exception>()) evaluates to
true.
- Sets only have set operators. We need relational operators as well;
besides, the cartesian product is defined differently (though
analogously) for sets and relations.
--
Jon
Received on Thu Mar 02 2006 - 08:14:12 CST
