40
Preliminary Definitions
Def:  A relational description DP is a sequence of
         relations  over a set of primitives P.
• Let DA = {R1,…,RI} be a relational description over A.
• Let DB = {S1,…,SI} be a relational description over B.
•
• Let f be a 1-1, onto mapping from A to B.
•
• For any relation R, the composition R°f is given by
 R°f = {(b1,…,bn) | (a1,…,an) is in R and f(ai)=(bi), i=1,n}