/**
   * Return the set of elements from the given side which have a match in the opposite side
   * according to the given comparison
   * @param comparison_p a non-null comparison
   * @param side_p TARGET or REFERENCE
   * @return a non-null collection containing no null value
   */
  public Collection<EObject> getCommonElements(IComparison comparison_p, Role side_p) {
    Collection<EObject> result = new HashSet<EObject>();
    for (IMatch match : comparison_p.getMapping().getContents()) {
      if (!match.isPartial())
        result.add(match.get(side_p));
    }
    return result;
  }