Programming

Unlike traditional client/server models, such as a Web server/Web page system, Web services do not provide the user with a GUI. Web services instead share business logic, data and processes through a programmatic interface across a network. The applications interface, not the users. Developers can then add the Web service to a GUI (such as a Web page or an executable program) to offer specific functionality to users.

Actually REST is the http. Roy Fielding described REST in his Ph.D dissertation. You do not need to use any sort of library like we used to use in SOAP based web services.
So yes in terms of the architecture and no in term of application.

REST is just a mechanism to interact with the server regardless of platform.  

Yeah! You know JQuery says: "Write less do more" and Yii  says "Write a line and leave rest on Yii". With the combination of Yii and JQuery the web service design becomes more efficient and scalable. Yii is the fastest and efficient PHP framework and JQuery is the most popular JavaScript framework. 

Hello World!

What you want to do first is to write the "hello world" thing. Not only you we all! Without doing code kastoori we will write a clean API.

Introduction to Yii

Yii is getting more popular among than any other PHP frameworks. Yii attracts smart developers due to its clean and component based MVC pattern.
Yii introduces many features and advance oop techniques which are not available in any existing PHP framework. This tutorial assumes that you already know the basics of Yii framework.

Base conroller for our API

As every Yii controller is inherited from CController. We will create our own base controller which will be inherited from CController.

class ApiController extends CController{
//Functionality
}

In the ApiConroller we will put all we needed functionality. One of this functionality we need is the generation of output i,e the JSON.
protected function sendResponse($status = 200, $body = '', $contentType = 'application/json')
{
// Set the status
$statusHeader = 'HTTP/1.1 ' . $status . ' ' .                     $this->getStatusCodeMessage($status);
header($statusHeader);
// Set the content type
header('Content-type: ' . $contentType);

echo $body;
Yii::app()->end();
}

To send appropriate headers also we put the function getStatusCodeMessage which assigns the status code in the JSON header. And the definition of this function goes here:

protected function getStatusCodeMessage($status)
{
   $codes = array(
100 => 'Continue',
101 => 'Switching Protocols',
200 => 'OK',
201 => 'Created',
202 => 'Accepted',
203 => 'Non-Authoritative Information',
204 => 'No Content',
205 => 'Reset Content',
206 => 'Partial Content',
300 => 'Multiple Choices',
301 => 'Moved Permanently',
302 => 'Found',
303 => 'See Other',
304 => 'Not Modified',
305 => 'Use Proxy',
306 => '(Unused)',
307 => 'Temporary Redirect',
400 => 'Bad Request',
401 => 'Unauthorized',
402 => 'Payment Required',
403 => 'Forbidden',
404 => 'Not Found',
405 => 'Method Not Allowed',
406 => 'Not Acceptable',
407 => 'Proxy Authentication Required',
408 => 'Request Timeout',
409 => 'Conflict',
410 => 'Gone',
411 => 'Length Required',
412 => 'Precondition Failed',
413 => 'Request Entity Too Large',
414 => 'Request-URI Too Long',
415 => 'Unsupported Media Type',
416 => 'Requested Range Not Satisfiable',
417 => 'Expectation Failed',
500 => 'Internal Server Error',
501 => 'Not Implemented',
502 => 'Bad Gateway',
503 => 'Service Unavailable',
504 => 'Gateway Timeout',
505 => 'HTTP Version Not Supported',
                        420 => 'Error'

   );
   return (isset($codes[$status])) ? $codes[$status] : '';
}

Now, we will inherit all our controllers from this base class ApiController. Suppose we have a student Model which posses all student related information such as ID, Name, grade etc. So we are going to write a service which will return all users with all info.

class StudentController extends ApiController{
   public function actionStudents(){
       $students = Students::model()->findAll();
       $this->sendResponse(200,CJSON::encode($students));
  }
}

Line by line analysis:

1- StudentController is inherited from ApiController which has the sendResponse function
2- The Student action which will be pointed by a URI.
3- A student object is initiated which has all student info
4- Sends the response in JSON string.

The CJSON::enchod() will convert the student object into JSON string. In our case the output string will be
[
{"id":"15","name":"Shahid","grade":"10"},
{"id":"16","name":"Kate","grade":"9"},
]

Well, the intelligent CJSON::encode() function have converted the student object into JSON array very cleanly.
To test your API hit http://localhost/yourservice/index.php/student/students

Hope you enjoyed!