Reference: http//:www.yiiframework.com

Yii Versions

There are two main versions of Yii

Yii 1.1

It is the initial and old generation and now-a-days it is in maintenance mode.

Yii 2.0

Yii 2.0 is the complete rewrite version of Yii that is enrich with latest technologies and protocols i.e. PSR, Namespaces, Traits and Composer etc.

Yii development team commit that yii 2.0 will grow more for main development.

Yii 1.1 vs Yii 2.0 :

there are some front end level changes in yii 2.0

• we can see that CHtml link is changed totally
• CMenu is changed
• CHtml image link is changed
• Breadcrumbs are changed

CHtml::link()

Html::a()

$this->widget('zii.widgets.CMenu', [
  'items'=>[
    [
      'label'=>'Home',
      'url'=>['site/index']
    ],
    [
      'label'=>'Home',
      'url'=>['site/index']
    ]
  ]
]);

echo Nav::widget(
  'items'=>[
    [
      'label'=>'Home',
      'url'=>['site/index']
    ],
    [
      'label'=>'Home',
      'url'=>['site/index']
    ]
  ]
);

CHtml::img(
  '/path/to/file',
  'alt-text', 
  ['class'=>'img-responsive']
);

Html::img(
  '/path/to/img',
  [
    'alt'=>'alt-text',
    'class'=>'img-responsive'
  ]
)

$this->breadcrumbs = [
  'Label'=>['site/labelAction'],
  'Current Page Title',
];

$this->params['breadcrumbs'] =[
  [
    'label'=>'Label',
    'url'=>['site/labelAction']
  ],
  'Current Page Title'
]; 

for more details see the Class Reference

The Change Log of Yii 2.0 (Under Development)

see Yii 2.0 change log

Yii 1.1 and Yii 2.0 Application Hierarchy/ Structure.

lets see the old and new hierarchies of Yii application.

Hierarchy/Structure of Yii 1.1.* Application

index.php
index-test.php
assets/
css/
images/
themes/
protected/
  commands/
  components/
  config/
  controllers/
  data/
  extensions/ 
  messages/
  models/
  runtime/
  tests/
  views/
framework             //located outside the web root

Structure of Yii 2.0 Basic Application

Yii 2.0 basic application is for small projects or when you’re just learning the framework.

assets/   // This is *NOT* the web accessible assets folder
commands/
config/
controllers/
mail/
models/
runtime/
tests/
vendor/
  yiisoft/  <-- equivalent to the "framework" folder
  ezyang
  twbs
  ... <-- Composer installed dependencies (extensions)
views/
web/       <-- The web root for your application
  index.php
  index-test.php
  assets/  <-- your published assets folder for the web
  css/

how to install  it?

Advanced Yii 2.0 Application Structure

This template is for large projects developed in teams where backend is divided from frontend, application is deployed to multiple servers etc.

backend/  <-- Site 1
  config/
  controllers/
  models/
  runtime/
  tests/
  views/
  web/       <-- The web root for your backend application
    index.php
    index-test.php
    assets/ 
    css/
common/
  config/
  mail/
  models/
  tests/
console/
environments/ 
frontend/
  config/
  controllers/
  models/
  runtime/
  tests/
  views/
  web/       <-- The web root for your frontend application
    index.php
    index-test.php
    assets/  
    css/
vendor/
  yiisoft/

how to install it?