Concepts & Features: A concept cover the whole range, a feature is constrained

time to read 2 min | 264 words

A while ago I mentioned the idea of Concepts and Features, I expounded it a bit more in the Feature by Feature post. Concepts and Features is the logical result of applying the Open Closed and Single Responsibility Principles. It boils down to a single requirement:

A feature creation may not involve any design activity.

Please read the original post for details about how this is actually handled. And a the specific example about filtering with NH Prof.

But while I put constraints on what a feature is, I haven’t talked about what a concept is. Oh, I talked about it being the infrastructure, but not much more.

The point about a concept implementation is that it contains everything that a feature must do. To take the filtering support in NH Prof as an example, the concept is responsible for finding all available filters, create and manage the UI, show the filter definition for the user when a filter is active, save and load the filter definition when the application is closed/started, perform the actual filtering, etc. The concept is also responsible for defining the appropriate conventions for the features in this particular concept.

As you can see, a lot of work goes into building a concept. But that work pays off the first time that you can service a user request in a rapid manner. To take NH Prof again, for most things, I generally need about half an hour to put out a new feature within an existing concept.