Modularity by Example

There are lots of benefits to modularity, some of which I discussed when introducing modularity patterns. But here’s a simple example, which serves as a prelude to some upcoming posts explaining a few of the patterns.

In the diagram at right (click to enlarge), the top left quadrant shows a sample system with a relatively complex class structure. When change occurs within a single class, shown in red in the bottom left quadrant, understanding the impact of change is difficult. It appears possible that it can propagate to any class dependent on the class highlighted in red.  Assessing the impact of change requires that we analyze the complete class structure. The ripple effect appears significant, and change instills fear.

But if the system is modular with classes allocated to these modules, as shown in the bottom right quadrant, then understanding the impact of change can be isolated to a discrete set of modules. And this makes it much easier to identify which modules contain classes that might also change, as shown in the top right quadrant. Change is isolated to classes within modules that are dependent on the module containing the class that is changing.

This is a simple example, but it serves as evidence of the need for modular architecture, and illustrates one reason why modularity is so important. Modularity makes understanding the system easier. It makes maintaining the system easier. And it makes reusing system modules much more likely. As systems grow in size and complexity, it’s imperative that we design more modular software. That means we need a module system for the Java platform. It means that module system shouldn’t be shielded from enterprise developers. And it means we need to understand the patterns that are going to provide the guidance necessary in helping us design more modular software.