For many that come briefly into contact with Extreme Programming, it seems that XP calls for the death of software design. Not just is much design activity ridiculed as “Big Up Front Design”, but such design techniques as the UML, flexible frameworks, and even patterns are de-emphasized or downright ignored. In fact XP involves a lot of design, but does it in a different way than established software processes. XP has rejuvenated the notion of evolutionary design with practices that allow evolution to become a viable design strategy. It also provides new challenges and skills as designers need to learn how to do a simple design, how to use refactoring to keep a design clean, and how to use patterns in an evolutionary style.

In the Java community there's been a rush of lightweight containers that help to assemble components from different projects into a cohesive application. Underlying these containers is a common pattern to how they perform the wiring, a concept they refer under the very generic name of “Inversion of Control”. In this article I dig into how this pattern works, under the more specific name of “Dependency Injection”, and contrast it with the Service Locator alternative. The choice between them is less important than the principle of separating configuration from use.

The Ruby Rogues are a popular podcast where a regular panel discusses topics in the Ruby programming community. They have a regular book club and recently selected P of EAA as their featured book. Consequently they asked me to appear as a guest on their show to discuss the book and the patterns that it describes, in particular the interesting relationship between these patterns and the Rails framework.

I was interviewed by Bill Venners for his artima.com web site. In the interview I touch upon refactoring, evolutionary design, flexibility, and test driven development. Bill even manages to make me sound coherent.

The organizers of QCon London 2007, asked me to do a conference session on modifiability of architecture. I thought that rather than listening to me, the audience might prefer listen to some of the Thoughtworks architects whose ideas I usually repackage: Dave Farley, Ian Cartwright, Fred George, Erik Doernenberg, and Daniel Terhorst-North. InfoQ has now put up a video of session.

Graphical User Interfaces provide a rich interaction between the user and a software system. Such richness is complex to manage, so it's important to contain that complexity with a thoughtful architecture. The Forms and Controls pattern works well for systems with a simple flow, but as it breaks down under the weight of greater complexity, most people turn to “Model-View-Controller” (MVC). Sadly MVC is one of the most misunderstood architectural patterns around, and systems using that name display a range of important differences, sometimes described under names like Application Model, Model-View-Presenter, Presentation Model, MVVM, and the like. The best way to think of MVC is as set of principles including the separation of presentation from domain logic and synchronizing presentation state through events (the observer pattern).

Towards the end of last year I attended a workshop with my colleagues in Thoughtworks to discuss the nature of “event-driven” applications. Over the last few years we've been building lots of systems that make a lot of use of events, and they've been often praised, and often damned. Our North American office organized a summit, and Thoughtworks senior developers from all over the world showed up to share ideas.

The biggest outcome of the summit was recognizing that when people talk about “events”, they actually mean some quite different things. So we spent a lot of time trying to tease out what some useful patterns might be. This note is a brief summary of the main ones we identified.