Clustering by use of relation
The elements are mainly SSEs, represented as sticks
A seed match is usually a pair of sticks
To decide if two compatible pairs (Ai,Bj) and (Ak,Bl) are consistent, an intern relation r is used
The pairs are consistent if r(Ai,Ak) is approximately equal to r(Bj,Bl)
r should satisfy the following: r(Ai,Ak) and r(Bj,Bl) should be approximately equal if and only if the substructures (Ai,Ak) and (Bj,Bl) are considered as similar
r should be invariant with respect to rotation and translation, and in most cases to sequential order