// This file is part of OpenTSDB.
// Copyright (C) 2015  The OpenTSDB Authors.
//
// This program is free software: you can redistribute it and/or modify it
// under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 2.1 of the License, or (at your
// option) any later version.  This program is distributed in the hope that it
// will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty
// of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
// General Public License for more details.  You should have received a copy
// of the GNU Lesser General Public License along with this program.  If not,
// see <http://www.gnu.org/licenses/>.
package net.opentsdb.query.expression;

import java.util.List;

import net.opentsdb.core.DataPoints;
import net.opentsdb.core.TSQuery;

public interface Expression {

  public DataPoints[] evaluate(TSQuery data_query, 
      List<DataPoints[]> results, List<String> params);

  public String writeStringField(List<String> params, String inner_expression);
  
}

@@ -877,38 +877,570 @@
 y;%0A%0A
-public interface Expression %7B%0A
+/**%0A * The interface for various expressions/functions used when querying OpenTSDB.%0A * @since 2.3%0A */%0Apublic interface Expression %7B%0A%0A  /**%0A   * Computes a set of results given the results of a %7B@link TSQuery%7D that may%0A   * include multiple metrics and/or group by result sets.%0A   * @param data_query The original query from the user%0A   * @param results The results of the query%0A   * @param params Parameters parsed from the expression endpoint related to%0A   * the implementing function%0A   * @return An array of data points resulting from the implementation%0A   */
 %0A  p
@@ -1545,16 +1545,114 @@
 rams);%0A%0A
+  /**%0A   * TODO - document me!%0A   * @param params%0A   * @param inner_expression%0A   * @return%0A   */%0A
   public

Add some notes to the Expression interface.