code: RelationBuilder getRelationBuilder(Object target, Relation relation, Node source)
      {
          RelationBuilder relationBuilder = new RelationBuilder(target, relation, source);
          relationBuilder.assignGraphGenerator(this.generator);
          return relationBuilder;
      }
docs: Returns relation builder instance.
  
  @param target
  relational entity
  @param relation
  relation
  @param source
  relation originator entity
  @return relation builder instance.