public Dependency getDependency(Operator<? extends OperatorDesc> op,
      ColumnInfo col) {
      Map<ColumnInfo, Dependency> colMap = depMap.get(op);
      if (colMap == null) {
        return null;
      }

      return colMap.get(col);
    }
Gets the dependency for an operator, columninfo tuple.
@param op The operator whose dependency is being inspected.
@param col The column info whose dependency is being inspected.
@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