code: private int comparePrecedence(char sourceRelation, char targetRelation) {
          int result = -1;
  
          int sourcePrecedence = getPrecedenceNumber(sourceRelation);
          int targetPrecedence = getPrecedenceNumber(targetRelation);
          if (sourcePrecedence < targetPrecedence) {
              result = 1;
          } else if (sourcePrecedence == targetPrecedence) {
              result = 0;
          } else {
              result = -1;
          }
  
          return result;
      }
docs: Compares the semantic relation of the source and target in the order of precedence
  = > < ! ?. Returning -1 if sourceRelation is less precedent than targetRelation,
  0 if sourceRelation is equally precedent than targetRelation,
  1 if sourceRelation  is more precedent than targetRelation.
  
  @param sourceRelation source relation from IMappingElement.
  @param targetRelation target relation from IMappingElement.
  @return -1 if sourceRelation is less precedent than targetRelation,
  0 if sourceRelation is equally precedent than targetRelation,
  1 if sourceRelation  is more precedent than targetRelation.