code: private String getAlias(String schema, String table, String column, int stepDepth) {
          //PropertyType is not part of equals or hashCode so not needed for the lookup.
          Column c = new Column(schema, table, column, null, stepDepth);
          return columns.get(c);
      }
docs: get an alias if the column is already in the list
  
  @param schema
  @param table
  @param column
  @return