public Dependency getDependency(
        Operator<? extends OperatorDesc> op, String internalName) {
      Map<ColumnInfo, Dependency> colMap = depMap.get(op);
      if (colMap != null) {
        for (Map.Entry<ColumnInfo, Dependency> e: colMap.entrySet()) {
          if (e.getKey().getInternalName().equals(internalName)) {
            return e.getValue();
          }
        }
      }
      return null;
    }
Gets the dependency for a tuple of an operator,
and a ColumnInfo with specified internal name.

@param op The operator whose dependency is being inspected.
@param internalName The internal name of the column info
@return Dependency for that particular operator, ColumnInfo tuple.
        null if no dependency is found.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/lineage/LineageCtx.java