General Relations
For databases, we are nearly always interested in n-ary relations between distinct domains, e.g. assume:
Login = {wcao, Flora, Fulay, zyr98210, jin0328}
LastName = {Cao, Flora, Fulay, Zhang}
Dept = {CSIT, EE, CS}
then we may define the relation:
Students, on Login ? LastName ? Dept :
{ (wcao, Cao, CSIT),
(Flora, Flora, EE ),
(Fulay, Fulay, CS ),
(zyr98210, Zhang, CS ),
(jin0328, Zhang, CS ) }