code: public static boolean sameSubject(SubjectNode s1, String s2) {
          if (s1 instanceof URIReference) {
              return sameResource((URIReference) s1, s2);
          } else {
              return false;
          }
      }
docs: Tells whether the given subjects are equivalent, with one given as a URI
  string.
  
  @param s1
  first subject.
  @param s2
  second subject, given as a URI string.
  @return true if equivalent, false otherwise.