code: protected static String createKey(CmsUUID source, CmsUUID target, String relType) {
  
          return RELATION_ID_PREFIX + source + "_" + target + "_" + relType;
      }
docs: Creates a relation id string from the source and target ids and a relation type.<p>
  
  @param source the source id
  @param target the target id
  @param relType the relation type
  
  @return the relation id