code: function(requestId, itemName, isSnapshot, data) {
  		return protocol.implodeMessage(protocol.timestamp(), dataMethods.UPDATE_BY_MAP,
  			types.STRING, protocol.encodeString(itemName),
  			types.STRING, requestId,
  			types.BOOLEAN, protocol.encodeBoolean(isSnapshot),
  			protocol.implodeData(data));
  	}
docs: Encodes an update for a particular item to be sent to the proxy.
  
  @param {String} requestId the originating request id
  @param {String} itemName the item name
  @param {Boolean} isSnapshot if the data is a complete snapshot
  @param {Object} data a flat associative array built using simple primitive data
  types that represents the update record
  @return {String} the encoded message
  @private