Running Applications
====================

You now have a working Yii application which can be accessed via URL `http://hostname/index.php`.
In this section, we will introduce what functionalities this application has, how the code is organized,
and how the application handles requests in general.

> Info: For simplicity, throughout this "Getting Started" tutorial we assume that you have set `basic/web`
  as the document root of your Web server. If you have not done so, the URL for accessing
  your application could be `http://hostname/basic/web/index.php`, or something similar.
  Please adjust the URLs accordingly in our descriptions.


Functionalities
---------------

The application that you have installed contains four pages:

* the homepage is the page displayed when you access the URL `http://hostname/index.php`;
* the "About" page;
* the "Contact" page displays a contact form that allows end users to contact you by filling out the form;
* the "Login" page displays a login form that can be used to authenticate end users. Try logging in
  with "admin/admin", and you will find the "Login" main menu item will change to "Logout".

These pages share a common header and footer. The header contains a main menu bar to allow navigate
among different pages.

You should also see a toolbar sticking at the bottom of the browser window when it displays any of the above pages.
This is a useful [debugger tool](tool-debugger.md) provided by Yii to help you check various debugging information
about the application execution, such as log messages, response status, database queries, and so on.


Application Structure
---------------------

The following is a list of the most important directories and files in your application,

```
basic/                  application base path
    composer.json       used by Composer, describes package information
    config/             contains application and other configurations
        console.php     the console application configuration
        web.php         the Web application configuration
    commands/           contains console command classes
    controllers/        contains controller classes
    models/             contains model classes
    runtime/            contains files generated by Yii during runtime, such as logs, cache files
    vendor/             contains the installed Composer packages, including the Yii framework
    views/              contains view files
    web/                application Web root, contains Web accessible files
        assets/         contains published asset files (js, css) by Yii
        index.php       the entry script of the application
    yii                 the Yii console command execution script
```

In general, the files in the application can be divided into two parts: those under `basic/web` and those
under other directories. The former can be directly accessed from Web, while the latter can not and should not.

Yii implements the [model-view-controller (MVC)](http://wikipedia.org/wiki/Model-view-controller) design pattern
which is reflected in the above directory organization. The `models` directory contains all [model classes](structure-models.md),
the `views` directory contains all [view scripts](structure-views.md), and the `controllers` directory contains
all [controller classes](structure-controllers.md).

The following diagram shows the static structure of an application.

![Static Structure of Application](images/application-structure.png)

Each application has an entry script `web/index.php` which is the only Web accessible PHP script in the application.
The entry script takes an incoming request and creates an [application](structure-applications.md) instance to handle it.
The [application](structure-applications.md) resolves the request with the help of its [components](concept-components.md)
and dispatches the request to MVC. [Widgets](structure-widgets.md) are used in the [views](structure-views.md)
to help build complex and dynamic user interface elements.


Request Lifecycle
-----------------

The following diagram shows how an application handles a request.

![Request Lifecycle](images/application-lifecycle.png)

1. A user makes a request to the [entry script](structure-entry-scripts.md) `web/index.php`.
2. The entry script loads the application [configuration](concept-configurations.md) and creates
   an [application](structure-applications.md) instance to handle the request.
3. The application resolves the requested [route](runtime-routing.md) with the help of
   the [request](runtime-requests.md) application component.
4. The application creates a [controller](structure-controllers.md) instance to handle the request.
5. The controller creates an [action](structure-controllers.md) instance and performs the filters for the action.
6. If any filter fails, the action is cancelled.
7. If all filters pass, the action is being executed.
8. The action loads a data model, possibly from a database.
9. The action renders a view with the data model.
10. The rendering result is to the [response](runtime-responses.md) application component.
11. The response component sends the rendering result to the user.

