Joomla! Architecture: Extensions

An extension is a package that extends your Joomla! installation in some way. A small selection of extensions is included with the default Joomla! installation but many more are available from the Joomla! Extensions Site.  

The term “extension” is generic and the following specific extension types are available (listed alphabetically): 

• Component
• Language
• Library in Joomla! 1.6 onwards
• Mambot in Joomla 1.0.x only (in later versions Mambots are referred to as Plugins)
• Module
• Package in Joomla! 1.6 onwards
• Plugin from Joomla! 1.5.0 onwards (formerly known as Mambots)
• Template

Joomla! extensions illustrated

Joomla! Component

A component is the largest and most complex extension of them all, they can be seen as mini-applications. There are two parts in a component, an administrator part and a site part. Every time a Joomla page loads, a component is called to render the main page body. For example, com_registration is the component which handles user registration, users can sign up as a member at the frontend of your site and, as an administrator, you can edit these users. Components are the major portion of your page because a component is driven by a menu item and every menu item runs a component.  

Joomla! Module

Modules are lightweight and flexible extensions used for page rendering. Sometimes modules are linked to components such as the “latest news” module which links to the content component (com_content) and displays links to the newest content items. These modules are mostly visible as the “boxes” that are arranged around a component on a typical page, for example, the login module. Modules are assigned per menu item, so, for example, you can decide to show or hide the logon module depending on which component (menu item) is used. However, modules do not need to be linked to components; they don’t even need to be linked to anything and can be just static HTML or text.  

Joomla! Plugin

A plugin is a kind of Joomla! extension. Plugins are in essence event handlers and provide routines which are associated with trigger events within Joomla. When a particular trigger event occurs all plugin routines of the type associated with the event are executed in sequence. In the execution of any part of Joomla, be it the core, a module or a component, an event can be triggered. When an event is triggered, plugins that are registered with the application to handle that event execute. In this way it is possible to add functionality to the Joomla Framework.  

How to Create a Joomla! Plugin  

Joomla! Template

A template is the type of Joomla! extension that changes the way your site looks. A template is basically the design of your Joomla! powered website. With a template you can change the look and feel of your website. Templates have certain fields in which components and modules will be shown. Templates are easy to build or customize and they provide maximum flexibility in how you style your site. There are two types of templates: Front-end Templates and Back-end Templates. Front-end templates change the way your site looks to average users. Most of the templates you use will be Front-end Templates.

There are some templates that were made in the Joomla! 1.5 Template Contest. There are also many websites where both free and non-free Joomla! templates can be downloaded. 

Tutorial: Creating a basic Joomla! template

Joomla! Language

Probably the most basic extensions are languages. Languages can be packaged in two ways, either as a core package or as an extension package. In essence, these files consist key/value pairs, these pairs provide the translation of static text strings which are assigned within the Joomla! source code. These language packs will affect both the front and administrator side. Note: these language packs also include an XML meta file which describes the language and font information to use for PDF content generation.