ThoughtShapes Shaping Ideas With Thought

The work a system does and the interface to that work should be separated from one another. This is a concept that evolves from the Single Responsibility Principle and from Test Driven Development. Whether this work be hosted in a console program, a GUI program, exposed as a service for outside systems to utilize, or any other possible configuration, follow SRP and keep the work separate from the hosting interface that exposes the work to a client (a client in this case can be a person or another software system).

Rjae, Rob, Kasia Baron, and I went to the Deep Agile 2008 conference run by New England Agile Bazaar. The event was held over the course of two days at MIT's Tang Hall and was truly outstanding. The structure of it, as noted at Agile Bazaar's website, was a one-on-one discussion, debate-style, between Robert Martin and James Coplien and it focused on the realities of Agile software development.

I see a great many projects start off on the wrong foot by trying to decide all of their implementation technologies at the beginning of a project. Usually there’s a project kick-off meeting where everyone flies in from various locations to get introduced to all of the players and decide on things like what database engine are we going to use? What technology will we use to handle our data access? What user interface technologies should we use? Should we use web services?

We present the following principles:

• SRP: Single Responsibility Principle
• OCP: Open-Closed Principle
• LSP: Liskov Substituation Principle
• DIP: Dependency Inversion Principle
• ISP: Interface Segregation Principle

In the next session(s) we will be focusing on how to make one’s tests database independent. This includes two primary goals:

Adherents to Domain Driven Design (DDD) often struggle with how to structure the “layers” of their application with respect to where object repositories should be placed. As usual in software development the answer to this quandary is “It depends”. In this posting I’ll discuss several things that should be taken into consideration when making this decision.