Supported relations

// Directed relations
A.b    -> B;
A.b?   -> B;
A.bs*  -> B;
B      <- A.b  ;
B      <- A.b? ;
B      <- A.bs*;

// Bidirectional relations
A.b   <-> B.a;
A.b   <-> B.a?;
A.b   <-> B.as*;
A.b?  <-> B.a;
A.b?  <-> B.a?;
A.b?  <-> B.as*;
A.bs* <-> B.a;
A.bs* <-> B.a?;
A.bs* <-> B.as*;