When r and S are two relations from set A to B and B to C respectively, we can define a relation SoR from A to C such that
(a.c) Є SoR imples for all b Є B subject to the relations (a,b) ЄR and (b.c) ЄS.
SoR is called the composition of R and S.
Properties of SoR
In general RoS is not equal to SoR.
(SoR) - = R-oS-