diff --git a/src/mibew/js/compiled/chat/mibewapi_chat_interaction.js b/src/mibew/js/compiled/chat/mibewapi_chat_interaction.js
index 5bd4abfe..564c731a 100644
--- a/src/mibew/js/compiled/chat/mibewapi_chat_interaction.js
+++ b/src/mibew/js/compiled/chat/mibewapi_chat_interaction.js
@@ -5,4 +5,4 @@
  You may obtain a copy of the License at
      http://www.apache.org/licenses/LICENSE-2.0
 */
-MibewAPIChatInteraction=function(){this.obligatoryArguments={"*":{threadId:null,token:null,"return":{},references:{}},result:{errorCode:0}};this.getReservedFunctionsNames=function(){return["result"]}};MibewAPIChatInteraction.prototype=new MibewAPIInteraction;
+MibewAPIChatInteraction=function(){this.mandatoryArguments=function(){return{"*":{threadId:null,token:null,"return":{},references:{}},result:{errorCode:0}}};this.getReservedFunctionsNames=function(){return["result"]}};MibewAPIChatInteraction.prototype=new MibewAPIInteraction;
diff --git a/src/mibew/js/compiled/chat_app.js b/src/mibew/js/compiled/chat_app.js
index 929b8437..90f617e5 100644
--- a/src/mibew/js/compiled/chat_app.js
+++ b/src/mibew/js/compiled/chat_app.js
@@ -11,7 +11,7 @@
  You may obtain a copy of the License at
      http://www.apache.org/licenses/LICENSE-2.0
 */
-MibewAPIChatInteraction=function(){this.obligatoryArguments={"*":{threadId:null,token:null,"return":{},references:{}},result:{errorCode:0}};this.getReservedFunctionsNames=function(){return["result"]}};MibewAPIChatInteraction.prototype=new MibewAPIInteraction;
+MibewAPIChatInteraction=function(){this.mandatoryArguments=function(){return{"*":{threadId:null,token:null,"return":{},references:{}},result:{errorCode:0}}};this.getReservedFunctionsNames=function(){return["result"]}};MibewAPIChatInteraction.prototype=new MibewAPIInteraction;
 /*
  Copyright 2005-2013 the original author or authors.
  Licensed under the Apache License, Version 2.0 (the "License").
diff --git a/src/mibew/js/compiled/mibewapi.js b/src/mibew/js/compiled/mibewapi.js
index 46c4c74e..45448954 100644
--- a/src/mibew/js/compiled/mibewapi.js
+++ b/src/mibew/js/compiled/mibewapi.js
@@ -6,15 +6,14 @@
      http://www.apache.org/licenses/LICENSE-2.0
 */
 function MibewAPI(a){this.protocolVersion="1.0";if("object"!=typeof a||!(a instanceof MibewAPIInteraction))throw Error("Wrong interaction type");this.interaction=a}
-MibewAPI.prototype.checkFunction=function(a,b){if("undefined"==typeof a["function"]||""==a["function"])throw Error("Cannot call for function with no name");if(b)for(var c=this.interaction.getReservedFunctionsNames(),d=0;d<c.length;d++)if(a["function"]==c[d])throw Error("'"+a["function"]+"' is reserved function name");if("object"!=typeof a.arguments)throw Error("There are no arguments in '"+a["function"]+"' function");var c=0,f=this.interaction.getObligatoryArguments(a["function"]),e;a:for(e in a.arguments)for(d=
-0;d<f.length;d++)if(e==f[d]){c++;continue a}if(c!=f.length)throw Error("Not all obligatory arguments are set in '"+a["function"]+"' function");};MibewAPI.prototype.checkRequest=function(a){if("string"!=typeof a.token){if("undefined"==typeof a.token)throw Error("Empty token");throw Error("Wrong token type");}if(""==a.token)throw Error("Empty token");if("object"!=typeof a.functions||!(a.functions instanceof Array)||0==a.functions.length)throw Error("Empty functions set");for(var b=0;b<a.functions.length;b++)this.checkFunction(a.functions[b])};
+MibewAPI.prototype.checkFunction=function(a,b){if("undefined"==typeof a["function"]||""==a["function"])throw Error("Cannot call for function with no name");if(b)for(var d=this.interaction.getReservedFunctionsNames(),c=0;c<d.length;c++)if(a["function"]==d[c])throw Error("'"+a["function"]+"' is reserved function name");if("object"!=typeof a.arguments)throw Error("There are no arguments in '"+a["function"]+"' function");var d=0,f=this.interaction.getMandatoryArguments(a["function"]),e;a:for(e in a.arguments)for(c=
+0;c<f.length;c++)if(e==f[c]){d++;continue a}if(d!=f.length)throw Error("Not all mandatory arguments are set in '"+a["function"]+"' function");};MibewAPI.prototype.checkRequest=function(a){if("string"!=typeof a.token){if("undefined"==typeof a.token)throw Error("Empty token");throw Error("Wrong token type");}if(""==a.token)throw Error("Empty token");if("object"!=typeof a.functions||!(a.functions instanceof Array)||0==a.functions.length)throw Error("Empty functions set");for(var b=0;b<a.functions.length;b++)this.checkFunction(a.functions[b])};
 MibewAPI.prototype.checkPackage=function(a){if("undefined"==typeof a.signature)throw Error("Missed package signature");if("undefined"==typeof a.proto)throw Error("Missed protocol version");if(a.proto!=this.protocolVersion)throw Error("Wrong protocol version");if("undefined"==typeof a.async)throw Error("'async' flag is missed");if("boolean"!=typeof a.async)throw Error("Wrong 'async' flag value");if("object"!=typeof a.requests||!(a.requests instanceof Array)||0==a.requests.length)throw Error("Empty requests set");
-for(var b=0;b<a.requests.length;b++)this.checkRequest(a.requests[b])};MibewAPI.prototype.getResultFunction=function(a,b){"undefined"==typeof b&&(b=null);var c=null,d;for(d in a)if(a.hasOwnProperty(d)&&"result"==a[d]["function"]){if(null!==c)throw Error("Function 'result' already exists in functions list");c=a[d]}if(!0===b&&null===c)throw Error("There is no 'result' function in functions list");if(!1===b&&null!==c)throw Error("There is 'result' function in functions list");return c};
-MibewAPI.prototype.buildResult=function(a,b){var c=this.interaction.getObligatoryArgumentsDefaults("result"),d;for(d in c)c.hasOwnProperty(d)&&(a[d]=c[d]);return{token:b,functions:[{"function":"result",arguments:a}]}};MibewAPI.prototype.encodePackage=function(a){var b={signature:""};b.proto=this.protocolVersion;b.async=!0;b.requests=a;return encodeURIComponent(JSON.stringify(b)).replace(/\%20/gi,"+")};
-MibewAPI.prototype.decodePackage=function(a){a=JSON.parse(decodeURIComponent(a.replace(/\+/gi," ")));this.checkPackage(a);return a};function MibewAPIInteraction(){this.obligatoryArguments={};this.getReservedFunctionsNames=function(){return[]}}
-MibewAPIInteraction.prototype.getObligatoryArguments=function(a){var b=[];if("object"==typeof this.obligatoryArguments["*"])for(var c in this.obligatoryArguments["*"])this.obligatoryArguments["*"].hasOwnProperty(c)&&b.push(c);if("object"==typeof this.obligatoryArguments[a])for(c in this.obligatoryArguments[a])this.obligatoryArguments[a].hasOwnProperty(c)&&b.push(c);return b};
-MibewAPIInteraction.prototype.getObligatoryArgumentsDefaults=function(a){var b={};if("object"==typeof this.obligatoryArguments["*"])for(var c in this.obligatoryArguments["*"])this.obligatoryArguments["*"].hasOwnProperty(c)&&(b[c]=this.obligatoryArguments["*"][c]);if("object"==typeof this.obligatoryArguments[a])for(c in this.obligatoryArguments[a])this.obligatoryArguments[a].hasOwnProperty(c)&&(b[c]=this.obligatoryArguments[a][c]);return b};
-function MibewAPIExecutionContext(){this.returnValues={};this.functionsResults=[]}
-MibewAPIExecutionContext.prototype.getArgumentsList=function(a){var b=a.arguments,c=a.arguments.references,d,f,e;for(e in c)if(c.hasOwnProperty(e)){f=c[e];if("undefined"==typeof this.functionsResults[f-1])throw Error("Wrong reference in '"+a["function"]+"' function. Function #"+f+" does not call yet.");if("undefined"==typeof b[e]||""==b[e])throw Error("Wrong reference in '"+a["function"]+"' function. Empty '"+e+"' argument.");d=b[e];if("undefined"==typeof this.functionsResults[f-1][d])throw Error("Wrong reference in '"+
-a["function"]+"' function. There is no '"+d+"' argument in #"+f+" function results");b[e]=this.functionsResults[f-1][d]}return b};MibewAPIExecutionContext.prototype.getResults=function(){return this.returnValues};
-MibewAPIExecutionContext.prototype.storeFunctionResults=function(a,b){var c;if(b.errorCode)this.returnValues.errorCode=b.errorCode,this.returnValues.errorMessage=b.errorMessage||"";else for(var d in a.arguments["return"])if(a.arguments["return"].hasOwnProperty(d)){c=a.arguments["return"][d];if("undefined"==typeof b[d])throw Error("Variable with name '"+d+"' is undefined in the results of the '"+a["function"]+"' function");this.returnValues[c]=b[d]}this.functionsResults.push(b)};
+for(var b=0;b<a.requests.length;b++)this.checkRequest(a.requests[b])};MibewAPI.prototype.getResultFunction=function(a,b){"undefined"==typeof b&&(b=null);var d=null,c;for(c in a)if(a.hasOwnProperty(c)&&"result"==a[c]["function"]){if(null!==d)throw Error("Function 'result' already exists in functions list");d=a[c]}if(!0===b&&null===d)throw Error("There is no 'result' function in functions list");if(!1===b&&null!==d)throw Error("There is 'result' function in functions list");return d};
+MibewAPI.prototype.buildResult=function(a,b){var d=this.interaction.getMandatoryArgumentsDefaults("result"),c;for(c in d)d.hasOwnProperty(c)&&(a[c]=d[c]);return{token:b,functions:[{"function":"result",arguments:a}]}};MibewAPI.prototype.encodePackage=function(a){var b={signature:""};b.proto=this.protocolVersion;b.async=!0;b.requests=a;return encodeURIComponent(JSON.stringify(b)).replace(/\%20/gi,"+")};
+MibewAPI.prototype.decodePackage=function(a){a=JSON.parse(decodeURIComponent(a.replace(/\+/gi," ")));this.checkPackage(a);return a};function MibewAPIInteraction(){this.mandatoryArguments=function(){return{}};this.getReservedFunctionsNames=function(){return[]}}
+MibewAPIInteraction.prototype.getMandatoryArguments=function(a){var b=this.mandatoryArguments(),d=[];if("object"==typeof b["*"])for(var c in b["*"])b["*"].hasOwnProperty(c)&&d.push(c);if("object"==typeof b[a])for(c in b[a])b[a].hasOwnProperty(c)&&d.push(c);return d};
+MibewAPIInteraction.prototype.getMandatoryArgumentsDefaults=function(a){var b=this.mandatoryArguments(),d={};if("object"==typeof b["*"])for(var c in b["*"])b["*"].hasOwnProperty(c)&&(d[c]=b["*"][c]);if("object"==typeof b[a])for(c in b[a])b[a].hasOwnProperty(c)&&(d[c]=b[a][c]);return d};function MibewAPIExecutionContext(){this.returnValues={};this.functionsResults=[]}
+MibewAPIExecutionContext.prototype.getArgumentsList=function(a){var b=a.arguments,d=a.arguments.references,c,f,e;for(e in d)if(d.hasOwnProperty(e)){f=d[e];if("undefined"==typeof this.functionsResults[f-1])throw Error("Wrong reference in '"+a["function"]+"' function. Function #"+f+" does not call yet.");if("undefined"==typeof b[e]||""==b[e])throw Error("Wrong reference in '"+a["function"]+"' function. Empty '"+e+"' argument.");c=b[e];if("undefined"==typeof this.functionsResults[f-1][c])throw Error("Wrong reference in '"+
+a["function"]+"' function. There is no '"+c+"' argument in #"+f+" function results");b[e]=this.functionsResults[f-1][c]}return b};MibewAPIExecutionContext.prototype.getResults=function(){return this.returnValues};
+MibewAPIExecutionContext.prototype.storeFunctionResults=function(a,b){var d;if(b.errorCode)this.returnValues.errorCode=b.errorCode,this.returnValues.errorMessage=b.errorMessage||"";else for(var c in a.arguments["return"])if(a.arguments["return"].hasOwnProperty(c)){d=a.arguments["return"][c];if("undefined"==typeof b[c])throw Error("Variable with name '"+c+"' is undefined in the results of the '"+a["function"]+"' function");this.returnValues[d]=b[c]}this.functionsResults.push(b)};
diff --git a/src/mibew/js/compiled/users/mibewapi_users_interaction.js b/src/mibew/js/compiled/users/mibewapi_users_interaction.js
index b68df266..f4acc3af 100644
--- a/src/mibew/js/compiled/users/mibewapi_users_interaction.js
+++ b/src/mibew/js/compiled/users/mibewapi_users_interaction.js
@@ -5,4 +5,4 @@
  You may obtain a copy of the License at
      http://www.apache.org/licenses/LICENSE-2.0
 */
-MibewAPIUsersInteraction=function(){this.obligatoryArguments={"*":{agentId:null,"return":{},references:{}},result:{errorCode:0}};this.getReservedFunctionsNames=function(){return["result"]}};MibewAPIUsersInteraction.prototype=new MibewAPIInteraction;
+MibewAPIUsersInteraction=function(){this.mandatoryArguments=function(){return{"*":{agentId:null,"return":{},references:{}},result:{errorCode:0}}};this.getReservedFunctionsNames=function(){return["result"]}};MibewAPIUsersInteraction.prototype=new MibewAPIInteraction;
diff --git a/src/mibew/js/compiled/users_app.js b/src/mibew/js/compiled/users_app.js
index 754dcf41..eb5c4637 100644
--- a/src/mibew/js/compiled/users_app.js
+++ b/src/mibew/js/compiled/users_app.js
@@ -45,7 +45,7 @@ a={hash:{},data:d};return c+=j((f=e.L10n||b.L10n,f?f.call(b,"visitors.table.head
  You may obtain a copy of the License at
      http://www.apache.org/licenses/LICENSE-2.0
 */
-MibewAPIUsersInteraction=function(){this.obligatoryArguments={"*":{agentId:null,"return":{},references:{}},result:{errorCode:0}};this.getReservedFunctionsNames=function(){return["result"]}};MibewAPIUsersInteraction.prototype=new MibewAPIInteraction;
+MibewAPIUsersInteraction=function(){this.mandatoryArguments=function(){return{"*":{agentId:null,"return":{},references:{}},result:{errorCode:0}}};this.getReservedFunctionsNames=function(){return["result"]}};MibewAPIUsersInteraction.prototype=new MibewAPIInteraction;
 /*
  Copyright 2005-2013 the original author or authors.
  Licensed under the Apache License, Version 2.0 (the "License").
diff --git a/src/mibew/js/source/chat/mibewapi_chat_interaction.js b/src/mibew/js/source/chat/mibewapi_chat_interaction.js
index 57a944bc..2c7a1347 100644
--- a/src/mibew/js/source/chat/mibewapi_chat_interaction.js
+++ b/src/mibew/js/source/chat/mibewapi_chat_interaction.js
@@ -12,16 +12,18 @@
  * @constructor
  */
 MibewAPIChatInteraction = function() {
-    this.obligatoryArguments = {
-        '*': {
-            'threadId': null,
-            'token': null,
-            'return': {},
-            'references': {}
-        },
-        'result': {
-            'errorCode': 0
-        }
+    this.mandatoryArguments = function() {
+        return {
+            '*': {
+                'threadId': null,
+                'token': null,
+                'return': {},
+                'references': {}
+            },
+            'result': {
+                'errorCode': 0
+            }
+        };
     };
 
     this.getReservedFunctionsNames = function() {
diff --git a/src/mibew/js/source/mibewapi.js b/src/mibew/js/source/mibewapi.js
index 8b1c3bba..a8568d94 100644
--- a/src/mibew/js/source/mibewapi.js
+++ b/src/mibew/js/source/mibewapi.js
@@ -71,22 +71,22 @@ MibewAPI.prototype.checkFunction = function(functionObject, filterReservedFuncti
             "' function"
         );
     }
-    var obligatoryArgumentsCount = 0;
-    var obligatoryArgumentsList = this.interaction.getObligatoryArguments(
+    var mandatoryArgumentsCount = 0;
+    var mandatoryArgumentsList = this.interaction.getMandatoryArguments(
         functionObject['function']
     );
     argumentsLoop:
     for (var argName in functionObject.arguments){
-        for (var i = 0; i < obligatoryArgumentsList.length; i++) {
-            if (argName == obligatoryArgumentsList[i]) {
-                obligatoryArgumentsCount++;
+        for (var i = 0; i < mandatoryArgumentsList.length; i++) {
+            if (argName == mandatoryArgumentsList[i]) {
+                mandatoryArgumentsCount++;
                 continue argumentsLoop;
             }
         }
     }
-    if (obligatoryArgumentsCount != obligatoryArgumentsList.length) {
+    if (mandatoryArgumentsCount != mandatoryArgumentsList.length) {
         throw new Error(
-            "Not all obligatory arguments are set in '" +
+            "Not all mandatory arguments are set in '" +
             functionObject["function"] + "' function"
         );
     }
@@ -223,7 +223,7 @@ MibewAPI.prototype.getResultFunction = function(functionsList, existance){
  */
 MibewAPI.prototype.buildResult = function(resultArguments, token) {
     var mergedArguments = resultArguments;
-    var defaultArguments = this.interaction.getObligatoryArgumentsDefaults('result');
+    var defaultArguments = this.interaction.getMandatoryArgumentsDefaults('result');
     for (var argName in defaultArguments) {
         if (! defaultArguments.hasOwnProperty(argName)) {
             continue;
@@ -283,28 +283,32 @@ MibewAPI.prototype.decodePackage = function(encodedPackage){
  */
 function MibewAPIInteraction(){
     /**
-     * Defines obligatory arguments and default values for them
+     * Defines mandatory arguments and default values for them
      *
      * Keys of the array are function names ('*' for all functions). Values are
-     * arrays of obligatory arguments with key for name of an argument and value
+     * arrays of mandatory arguments with key for name of an argument and value
      * for default value.
      *
      * For example:
      * <code>
-     * this.obligatoryArguments = {
-     *      '*': {
-     *          'return': {},
-     *          'references': {}
-     *      },
-     *      'result': {
-     *          'errorCode': 0
+     * this.mandatoryArguments = function() {
+     *      return {
+     *           '*': {
+     *               'return': {},
+     *               'references': {}
+     *           },
+     *           'result': {
+     *               'errorCode': 0
+     *           }
      *      }
      * }
      * </code>
-     * @type Object
+     * @returns {Object}
      * @private
      */
-    this.obligatoryArguments = {};
+    this.mandatoryArguments = function() {
+        return {};
+    }
 
     /**
      * Returns reserved (system) functions' names
@@ -321,62 +325,64 @@ function MibewAPIInteraction(){
 }
 
 /**
- * Returns obligatory arguments for the functionName function
+ * Returns mandatory arguments for the functionName function
  *
  * @param {String} functionName Function name
- * @returns {Array} An array of obligatory arguments
+ * @returns {Array} An array of mandatory arguments
  */
-MibewAPIInteraction.prototype.getObligatoryArguments = function(functionName) {
-    var obligatoryArguments = [];
-    // Add obligatory for all functions arguments
-    if (typeof this.obligatoryArguments['*'] == 'object') {
-        for (var arg in this.obligatoryArguments['*']) {
-            if (! this.obligatoryArguments['*'].hasOwnProperty(arg)) {
+MibewAPIInteraction.prototype.getMandatoryArguments = function(functionName) {
+    var allMandatoryArguments = this.mandatoryArguments();
+    var mandatoryArguments = [];
+    // Add mandatory for all functions arguments
+    if (typeof allMandatoryArguments['*'] == 'object') {
+        for (var arg in allMandatoryArguments['*']) {
+            if (! allMandatoryArguments['*'].hasOwnProperty(arg)) {
                 continue;
             }
-            obligatoryArguments.push(arg);
+            mandatoryArguments.push(arg);
         }
     }
-    // Add obligatory arguments for given function
-    if (typeof this.obligatoryArguments[functionName] == 'object') {
-        for (var arg in this.obligatoryArguments[functionName]) {
-            if (! this.obligatoryArguments[functionName].hasOwnProperty(arg)) {
+    // Add mandatory arguments for given function
+    if (typeof allMandatoryArguments[functionName] == 'object') {
+        for (var arg in allMandatoryArguments[functionName]) {
+            if (! allMandatoryArguments[functionName].hasOwnProperty(arg)) {
                 continue;
             }
-            obligatoryArguments.push(arg);
+            mandatoryArguments.push(arg);
         }
     }
-    return obligatoryArguments;
+    return mandatoryArguments;
 }
 
 /**
- * Returns default values of obligatory arguments for the functionName function
+ * Returns default values of mandatory arguments for the functionName function
  *
  * @param {String} functionName Function name
- * @returns {Object} An object fields names are obligatory arguments and
+ * @returns {Object} An object fields names are mandatory arguments and
  * values are default values of them
  */
-MibewAPIInteraction.prototype.getObligatoryArgumentsDefaults = function(functionName) {
-    var obligatoryArguments = {};
-    // Add obligatory for all functions arguments
-    if (typeof this.obligatoryArguments['*'] == 'object') {
-        for (var arg in this.obligatoryArguments['*']) {
-            if (! this.obligatoryArguments['*'].hasOwnProperty(arg)) {
+MibewAPIInteraction.prototype.getMandatoryArgumentsDefaults = function(functionName) {
+    var allMandatoryArguments = this.mandatoryArguments();
+    var mandatoryArguments = {};
+    // Add mandatory for all functions arguments
+    if (typeof allMandatoryArguments['*'] == 'object') {
+        for (var arg in allMandatoryArguments['*']) {
+            if (! allMandatoryArguments['*'].hasOwnProperty(arg)) {
                 continue;
             }
-            obligatoryArguments[arg] = this.obligatoryArguments['*'][arg];
+            mandatoryArguments[arg] = allMandatoryArguments['*'][arg];
         }
     }
-    // Add obligatory arguments for given function
-    if (typeof this.obligatoryArguments[functionName] == 'object') {
-        for (var arg in this.obligatoryArguments[functionName]) {
-            if (! this.obligatoryArguments[functionName].hasOwnProperty(arg)) {
+    // Add mandatory arguments for given function
+    if (typeof allMandatoryArguments[functionName] == 'object') {
+        for (var arg in allMandatoryArguments[functionName]) {
+            if (! allMandatoryArguments[functionName].hasOwnProperty(arg)) {
                 continue;
             }
-            obligatoryArguments[arg] = this.obligatoryArguments[functionName][arg];
+            mandatoryArguments[arg] = allMandatoryArguments[functionName][arg];
         }
     }
-    return obligatoryArguments;
+    return mandatoryArguments;
 }
 /**
  * End of MibewAPIInteraction class
diff --git a/src/mibew/js/source/users/mibewapi_users_interaction.js b/src/mibew/js/source/users/mibewapi_users_interaction.js
index ce15a9e2..23b4202d 100644
--- a/src/mibew/js/source/users/mibewapi_users_interaction.js
+++ b/src/mibew/js/source/users/mibewapi_users_interaction.js
@@ -12,16 +12,18 @@
  * @constructor
  */
 MibewAPIUsersInteraction = function() {
-    this.obligatoryArguments = {
-        '*': {
-            'agentId': null,
-            'return': {},
-            'references': {}
-        },
-        'result': {
-            'errorCode': 0
-        }
-    };
+    this.mandatoryArguments = function() {
+        return {
+            '*': {
+                'agentId': null,
+                'return': {},
+                'references': {}
+            },
+            'result': {
+                'errorCode': 0
+            }
+        };
+    }
 
     this.getReservedFunctionsNames = function() {
         return [
diff --git a/src/mibew/libs/classes/Mibew/API/API.php b/src/mibew/libs/classes/Mibew/API/API.php
index c61d6c5b..6f487ee9 100644
--- a/src/mibew/libs/classes/Mibew/API/API.php
+++ b/src/mibew/libs/classes/Mibew/API/API.php
@@ -196,13 +196,13 @@ class API
             );
         }
         $unset_arguments = array_diff(
-            $this->interaction->getObligatoryArguments($function['function']),
+            $this->interaction->getMandatoryArguments($function['function']),
             array_keys($function['arguments'])
         );
         if (!empty($unset_arguments)) {
             throw new APIException(
                 "Arguments '" . implode("', '", $unset_arguments) . "' must be set",
-                APIException::OBLIGATORY_ARGUMENTS_MISSED
+                APIException::MANDATORY_ARGUMENTS_MISSED
             );
         }
     }
@@ -264,7 +264,7 @@ class API
      */
     public function buildResult($token, $result_arguments)
     {
-        $arguments = $result_arguments + $this->interaction->getObligatoryArgumentsDefaults('result');
+        $arguments = $result_arguments + $this->interaction->getMandatoryArgumentsDefaults('result');
         $package = array(
             'token' => $token,
             'functions' => array(
diff --git a/src/mibew/libs/classes/Mibew/API/APIException.php b/src/mibew/libs/classes/Mibew/API/APIException.php
index e30f408e..7b78c612 100644
--- a/src/mibew/libs/classes/Mibew/API/APIException.php
+++ b/src/mibew/libs/classes/Mibew/API/APIException.php
@@ -71,9 +71,9 @@ class APIException extends \Exception
      */
     const NOT_VALID_JSON = 12;
     /**
-     * Some of the function's obligatory arguments are missed
+     * Some of the function's mandatory arguments are missed
      */
-    const OBLIGATORY_ARGUMENTS_MISSED = 13;
+    const MANDATORY_ARGUMENTS_MISSED = 13;
     /**
      * Request contains more than one result functions
      */
diff --git a/src/mibew/libs/classes/Mibew/API/Interaction/AbstractInteraction.php b/src/mibew/libs/classes/Mibew/API/Interaction/AbstractInteraction.php
index afc6f2a0..1b6092e9 100644
--- a/src/mibew/libs/classes/Mibew/API/Interaction/AbstractInteraction.php
+++ b/src/mibew/libs/classes/Mibew/API/Interaction/AbstractInteraction.php
@@ -34,83 +34,93 @@ abstract class AbstractInteraction
     abstract public function getReservedFunctionsNames();
 
     /**
-     * Defines obligatory arguments and default values for them
+     * Defines mandatory arguments and default values for them.
      *
-     * @var array Keys of the array are function names ('*' for all functions).
-     * Values are arrays of obligatory arguments with key for name of an
+     * This method implements "template method" design pattern.
+     *
+     * @return array Keys of the array are function names ('*' for all functions).
+     * Values are arrays of Mandatory arguments with key for name of an
      * argument and value for default value.
      *
      * For example:
      * <code>
-     * protected $obligatoryArguments = array(
-     *     '*' => array(
-     *         // Obligatory arguments for all functions are:
-     *         'return' => array(),     // 'return' with array() by default and
-     *         'references' => array()  // 'references' with array() by default
-     *     ),
+     * protected function mandatoryArguments()
+     * {
+     *     return array(
+     *         // Mandatory arguments for all functions are:
+     *         '*' => array(
+     *             // 'return' with array() by default and
+     *             'return' => array(),
+     *             // 'references' with array() by default
+     *             'references' => array(),
+     *         ),
      *
-     *     'result' => array(
      *         // There is an additional argument for the result function
-     *         'errorCode' => 0        // This is 'error_code' with 0 by default
-     *     )
-     * );
+     *         'result' => array(
+     *             // This is 'error_code' with 0 by default
+     *             'errorCode' => 0,
+     *         ),
+     *     );
+     * }
      * </code>
      */
-    protected $obligatoryArguments = array();
+    abstract protected function mandatoryArguments();
 
     /**
-     * Returns obligatory arguments for the $function_name function
+     * Returns mandatory arguments for the $function_name function
      *
      * @param string $function_name Function name
-     * @return array An array of obligatory arguments
+     * @return array An array of mandatory arguments
      */
-    public function getObligatoryArguments($function_name)
+    public function getMandatoryArguments($function_name)
     {
-        $obligatory_arguments = array();
-        // Add obligatory for all functions arguments
-        if (!empty($this->obligatoryArguments['*'])) {
-            $obligatory_arguments = array_merge(
-                $obligatory_arguments,
-                array_keys($this->obligatoryArguments['*'])
+        $all_mandatory_arguments = $this->mandatoryArguments();
+        $mandatory_arguments = array();
+        // Add mandatory for all functions arguments
+        if (!empty($all_mandatory_arguments['*'])) {
+            $mandatory_arguments = array_merge(
+                $mandatory_arguments,
+                array_keys($all_mandatory_arguments['*'])
             );
         }
-        // Add obligatory arguments for given function
-        if (!empty($this->obligatoryArguments[$function_name])) {
-            $obligatory_arguments = array_merge(
-                $obligatory_arguments,
-                array_keys($this->obligatoryArguments[$function_name])
+        // Add mandatory arguments for given function
+        if (!empty($all_mandatory_arguments[$function_name])) {
+            $mandatory_arguments = array_merge(
+                $mandatory_arguments,
+                array_keys($all_mandatory_arguments[$function_name])
             );
         }
 
-        return array_unique($obligatory_arguments);
+        return array_unique($mandatory_arguments);
     }
 
     /**
-     * Returns default values of obligatory arguments for the $function_name
+     * Returns default values of mandatory arguments for the $function_name
      * function
      *
      * @param string $function_name Function name
-     * @return array Associative array with keys are obligatory arguments and
+     * @return array Associative array with keys are mandatory arguments and
      *   values are default values of them
      */
-    public function getObligatoryArgumentsDefaults($function_name)
+    public function getMandatoryArgumentsDefaults($function_name)
     {
-        $obligatory_arguments = array();
-        // Add obligatory for all functions arguments
-        if (!empty($this->obligatoryArguments['*'])) {
-            $obligatory_arguments = array_merge(
-                $obligatory_arguments,
-                $this->obligatoryArguments['*']
+        $all_mandatory_arguments = $this->mandatoryArguments();
+        $mandatory_arguments = array();
+        // Add mandatory for all functions arguments
+        if (!empty($all_mandatory_arguments['*'])) {
+            $mandatory_arguments = array_merge(
+                $mandatory_arguments,
+                $all_mandatory_arguments['*']
             );
         }
-        // Add obligatory arguments for given function
-        if (!empty($this->obligatoryArguments[$function_name])) {
-            $obligatory_arguments = array_merge(
-                $obligatory_arguments,
-                $this->obligatoryArguments[$function_name]
+        // Add mandatory arguments for given function
+        if (!empty($all_mandatory_arguments[$function_name])) {
+            $mandatory_arguments = array_merge(
+                $mandatory_arguments,
+                $all_mandatory_arguments[$function_name]
             );
         }
 
-        return $obligatory_arguments;
+        return $mandatory_arguments;
     }
 }
diff --git a/src/mibew/libs/classes/Mibew/API/Interaction/ChatInteraction.php b/src/mibew/libs/classes/Mibew/API/Interaction/ChatInteraction.php
index 73b86391..af783a30 100644
--- a/src/mibew/libs/classes/Mibew/API/Interaction/ChatInteraction.php
+++ b/src/mibew/libs/classes/Mibew/API/Interaction/ChatInteraction.php
@@ -36,19 +36,23 @@ class ChatInteraction extends AbstractInteraction
     }
 
     /**
-     * Defines obligatory arguments and default values for them
-     * @var array
-     * @see \Mibew\API\Interaction\AbstractInteraction::$obligatoryArgumnents
+     * Defines mandatory arguments and default values for them.
+     *
+     * @return array
+     * @see \Mibew\API\Interaction\AbstractInteraction::mandatoryArguments
      */
-    protected $obligatoryArguments = array(
-        '*' => array(
-            'threadId' => null,
-            'token' => null,
-            'references' => array(),
-            'return' => array(),
-        ),
-        'result' => array(
-            'errorCode' => 0,
-        ),
-    );
+    protected function mandatoryArguments()
+    {
+        return array(
+            '*' => array(
+                'threadId' => null,
+                'token' => null,
+                'references' => array(),
+                'return' => array(),
+            ),
+            'result' => array(
+                'errorCode' => 0,
+            ),
+        );
+    }
 }
diff --git a/src/mibew/libs/classes/Mibew/API/Interaction/InviteInteraction.php b/src/mibew/libs/classes/Mibew/API/Interaction/InviteInteraction.php
index dd40a915..edb8585d 100644
--- a/src/mibew/libs/classes/Mibew/API/Interaction/InviteInteraction.php
+++ b/src/mibew/libs/classes/Mibew/API/Interaction/InviteInteraction.php
@@ -36,18 +36,22 @@ class InviteInteraction extends AbstractInteraction
     }
 
     /**
-     * Defines obligatory arguments and default values for them
-     * @var array
-     * @see \Mibew\API\Interaction\AbstractInteraction::$obligatoryArgumnents
+     * Defines mandatory arguments and default values for them.
+     *
+     * @return array
+     * @see \Mibew\API\Interaction\AbstractInteraction::mandatoryArguments
      */
-    protected $obligatoryArguments = array(
-        '*' => array(
-            'references' => array(),
-            'return' => array(),
-            'visitorId' => null,
-        ),
-        'result' => array(
-            'errorCode' => 0,
-        ),
-    );
+    protected function mandatoryArguments()
+    {
+        return array(
+            '*' => array(
+                'references' => array(),
+                'return' => array(),
+                'visitorId' => null,
+            ),
+            'result' => array(
+                'errorCode' => 0,
+            ),
+        );
+    }
 }
diff --git a/src/mibew/libs/classes/Mibew/API/Interaction/UsersInteraction.php b/src/mibew/libs/classes/Mibew/API/Interaction/UsersInteraction.php
index 97dd3583..a0464a7f 100644
--- a/src/mibew/libs/classes/Mibew/API/Interaction/UsersInteraction.php
+++ b/src/mibew/libs/classes/Mibew/API/Interaction/UsersInteraction.php
@@ -36,21 +36,25 @@ class UsersInteraction extends AbstractInteraction
     }
 
     /**
-     * Defines obligatory arguments and default values for them
-     * @var array
-     * @see \Mibew\API\Interaction\AbstractInteraction::$obligatoryArgumnents
+     * Defines mandatory arguments and default values for them.
+     *
+     * @return array
+     * @see \Mibew\API\Interaction\AbstractInteraction::mandatoryArguments
      */
-    protected $obligatoryArguments = array(
-        '*' => array(
-            'agentId' => null,
-            'references' => array(),
-            'return' => array(),
-        ),
-        'updateThreads' => array(
-            'revision' => 0,
-        ),
-        'result' => array(
-            'errorCode' => 0,
-        ),
-    );
+    protected function mandatoryArguments()
+    {
+        return array(
+            '*' => array(
+                'agentId' => null,
+                'references' => array(),
+                'return' => array(),
+            ),
+            'updateThreads' => array(
+                'revision' => 0,
+            ),
+            'result' => array(
+                'errorCode' => 0,
+            ),
+        );
+    }
 }