add notes for refactoring of engine interface

lib/shib/engines/dummyengine.js

@@ -10,10 +10,24 @@ Executer.prototype.setup = function(setups, callback){
   callback(null);
 };
 
-Executer.prototype.execute = function(query, callback){
+Executer.prototype.execute = function(jobname, query, callback){ //TODO: jobname -> queryid ( jobname generation should be done in each engines)
   callback(null, new Fetcher());
 };
 
+/*
+ * Fetcher
+ *
+ * schema(callback): callback(err, schema)
+ *  schema: {fieldSchemas: ['fieldname1', 'fieldname2', 'fieldname3', ...]}
+ *  //?? schema: ['fieldname1', 'fieldname2', ...]
+ *
+ * fetch(num, callback): callback(err, rows, cb)
+ *  num: rows to fetch (null == all)
+ *  rows: ["_col1value_\t_col2value_\t_col3value_", "_col1value_\t_col2value_\t_col3value_", ...]
+ *    no more rows exists if (rows === null || rows.length < 1 || (rows.length == 1 && rows[0].length < 1))
+ *  cb: callback function to call after iterative callback process
+ */
+
 Executer.prototype.end = function(){};
 
 var Monitor = exports.Monitor = function(){