@Override
  public boolean equals(Object obj) {
    if (obj == null || !(obj instanceof OpSignature)) {
      return false;
    }
    if (obj == this) {
      return true;
    }
    OpSignature o = (OpSignature) obj;
    return signatureCompare(o);
  }
Holds the signature of the operator; the keys are are the methods name marked by {@link Signature}.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/signature/OpSignature.java