This content has been written a long time ago. As such, it might not reflect my current thoughts anymore. I keep this page online because it might still contain valid information.

Component Driven Development: it's like Lego!

Did you ever hear about Component-Based Development? Maybe about Component Driven Development? Both concepts are the same, and if you’re involved in Symfony2, Spring, or something similar, then you do Component Driven Development (CDD).

It’s all about separation of concerns. You design components with their own logic, each component does one thing well, and only one thing. To separate business logic in self-contained components requires to focus on interactions between components. In other words, you have to think about right interfaces. To help you, UML provides a component diagram which allows you to easily show components, interfaces, and relations.

In a component diagram, a provided interface is modeled using the lollipop notation, and a required interface is modeled using the socket notation. Small squares represent ports, which are features with distinct interaction points. So, a port is an internal component of a classifier.

Most of the time, you won’t use this kind of diagram because you don’t like to draw UML diagrams :-). But, as I said previously, you probably know Component Driven Development if you know Symfony2 or Spring. These two frameworks use the Inversion of Control architectural pattern through the Dependency Injection design pattern (I consider IoC as an architectural pattern because it’s not a design pattern you can implement).

A well-known issue when you use Component Driven Development is how to manage dependencies between components, and how to instantiate all your components. Dependency Injection Container to the rescue! By describing component’s dependencies, and thanks to a container, you’ll write an highly decoupled application, with components you can reuse.

The main drawbacks are the time you’ll spend to think about your architecture, and to know how your components will interact (don’t forget UML in that case). So, try to find a component before to write your own. In the PHP world, we have magic things:

Since few months, I work on a project for a French startup, and it’s my first Component Driven Development experience. I started by listing all my needs (an OAuth client, a iCalendar parser, …). Then, I tried to find one component per point. And, as a glue, I decided to use Composer. After the end of the first sprint, I was a bit confused because I wrote two hundred lines of code (including some test classes), and the project was ever ready to use. I focused on the only important thing: the aim of the application.

Thanks to tools like npm, gem, composer, it’s like Lego!

Feel free to fork and edit this post if you found a typo, thank you so much! This post is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.


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