Joomla! is an award−winning content management system with a powerful extension system. This makes it easy for third−party developers to build code extending Joomla's core functionality without hacking or modifying the core code. Once an extension is developed, it can be packaged into a ZIP file for site administrators to upload and use. The people who manage Joomla!−based websites and want to use extensions need not know any programming at all. Once the ZIP file is uploaded, the extension is installed. The name Joomla! comes from the Swahili word 'jumla', meaning "all together" or "as a whole". When you install an extension in Joomla!, it blends in with the rest of the site; all the extensions truly appear "all together, as a whole". Chapter 1 gives an overview of how Joomla! works. The example project used throughout the book is also introduced. The three types of extensions (components, modules, and plug−ins) are covered along with descriptions of how they work together. Chapter 2 begins the development of the component used in the project. Initial entries are made in the database and toolbars for the back end are built. The general file structure of Joomla! is also introduced. Chapter 3 walks through the creation of the back−end interface for creating, editing, and deleting records in the project. Database table classes are introduced, as well as common HTML elements used to make the project blend in with other Joomla! extensions. Chapter 4 builds a front−end interface for listing and viewing records. Additionally, code to generate and interpret search−engine−friendly links is covered. The project is also expanded slightly when a commenting feature is added. Chapter 5 introduces a module used to list records on every page of the site. The module takes advantage of layouts, where the same data can be formatted differently depending on how the code is called. Some of the code is also separated out into a helper class so that the main code generating the module stays simple. Chapter 6 rewrites the component developed in Chapters 2, 3, and 4 so that it follows the Model, View, Controller design pattern. Controls over the publishing of records are introduced, in addition to an interface for removing offensive comments. More toolbars are added and the search−engine−friendly URL code is redesigned. Chapter 7 develops three plug−ins. The first plug−in finds the names of records in the database and turns them in to links to those records. A second plug−in displays a short summary of the record when certain code is added to content articles. Finally, another plug−in is designed so that records are pulled up along with Joomla! content searches. Chapter 8 adds configuration parameters to the component, module, and plug−ins. These are handled through XML and generate a predictable interface in the back end for setting options. Retrieving the values of these parameters is standardized through built−in functions. Chapter 9 expands the XML files used for parameters and adds a listing of all the files in each extension. Once this file is compressed along with the rest of the code into a ZIP archive, it is ready to be installed on another copy of Joomla! without any programmer intervention. Custom installation scripts and SQL code are also added to the component.