A vast majority of web development frameworks are built to work with the MVC (Model-View-Controller) architecture, where the application is separated into independent layers called models, views, and controllers. In MVC, we have a clear understanding of what goes where and when each of the layers will be integrated in the process.

So, the first thing most developers will look at is the availability of MVC in WordPress. Unfortunately WordPress is not built on top of the MVC architecture. This is one of the main reasons that developers refuse to choose it as a development framework. Even though it is not MVC, we can create a custom execution process to make it work like an MVC application. Unlike other frameworks, it won't have the full capabilities of MVC. But unavailability of an MVC architecture doesn't mean that we cannot develop quality applications with WordPress.

WordPress relies on procedural event-driven architecture with its action hooks and filter system. Once the user makes a request, these actions will get executed in a certain order to provide the response to the user. You can find the complete execution procedure at http://codex.wordpress.org/Plugin_API/Action_Reference.

In an event-driven architecture, both the model and controller code gets scattered throughout the theme files. In the upcoming chapters, we are going to look at how we can separate these concerns with the event-driven architecture, in order to develop maintainable applications.