The broken windows theory is a criminological theory of the normsetting and signalling effects of urban disorder and vandalism on additional crime and anti-social behavior. The theory states that monitoring and maintaining urban environments in a well-ordered condition may prevent further vandalism as well as an escalation into more serious crime.
Wikipedia, Broken windows theory
The theory is that fixing broken windows could be a method to combat further vandalism. Instead of letting a broken window turn into a broken door turn into a broken wall turn into a wrecked house, you would simply repair the windows as they break.
The basic idea can apply to many different areas of life, for example litter on the streets, neglecting to pay your bills, and so on. This is entropy at work; what requires effort to maintain will break down without a steady input of effort. If you would chart the phenomenon it would look something like an exponential function bottoming out due to diminishing returns (it requires less effort to maintain a low entropy state).
The maintenance of software is also subject to entropy. Software needs a constant input of effort to remain maintainable.
The team agrees on rules regarding documentation and specifications. They set up rules as to what type of code goes into which parts, what functions goes into which domains. The team agrees on rules as to testing and qc, a promise to refactor early and often. All the good stuff, yea.
The application is being developed, and its quality is according to the rules set up by the team. If the rules are good and the team follows them, good software will result.
After development the application goes into production and the team scales down, sometimes leaving a group of junior developers to maintain the application.
After release a host of bugs and design shortcomings appear, often within the first few months. Some will require little effort to fix, some will require more. Suddenly the team is dealing with fewer hours yet harsher deadlines. Users are phoning in demanding new releases.
At this point the senior developer (or architect) might have left the team and is now allocated to other projects.
Keeping software working
Without the understanding of the design, and the understanding of discipline, will the junior team continue refactoring? Updating specifications? Separation of code? Documentation? Testing? Qc?
All good habits that were agreed upon as critical during development are soon forgotten in the maintenance phase. Entropy and software rot sets in, shortcuts are being made, and the codebase goes beyond repair.
The truth is that it takes a good deal of effort to keep a codebase workable.
Graphing the effort in maintaining a codebase might look like a jigsaw. For every change maintainability goes down. You need effort to push it back up again; effort to keep the design working, keep the specs updated, test the changes, qc, and so on.
If the team neglects pushing it back into “good as new” for too long, it will degenerate past an event horizon where the only way out is do it all over again. There are too many broken windows and too much effort is required to make it “whole” again.
In the figure above, the red line describes changes to code. For every change quality and maintainability goes down as complexity increases. That is why for every new feature, there is an associated effort cost to make sure the design is working. That means reevaluating object models, refactoring code, rewriting automated tests, and so on.
- Team lacking understanding of overall design
- Inexperienced coders
- No specifications
- Time pressure
- No method in place to deal with code maintenance
In the figure above there is a sufficient input of effort to bring the codebase back to quality after each change. The codebase remains maintainable, and there are fewer bugs.
- Coders understand value of refactoring
- Coders understand overall design
- Structure is in place to deal with redesign and refactoring
- Unit testing is in place
- Team will question feature creep
Fighting software rot
Software rot will set in sooner or later. If it goes too far, the application becomes unmaintainable. We want to keep the quality high for as long as possible, and there are a few things that can be done prolong the active life of software. Many of these items come through keeping a good practice culture in the project where you don’t allow for broken windows.
- Understand that redesign takes time
- Be extremely wary of feature creep
- Keep conceptual integrity in mind when adding new features
- Don’t add new features when stability is an existing problem
- Team members knowledgeable of overall design will do the big changes
- Separation of code
- Unit testing in place will encourage refactoring
- Good specifications will encourage refactoring
You could argue that these items aren’t practical, and yes some applications are just too far gone to help. What is important is to understand that some applications are vastly more maintainable than others. With good maintainability, adding new and complex features actually takes very little time. On the other hand, if the team chooses to ignore software rot you will quickly find yourself with an unmaintainable application where even the smaller features take a long time to implement.
The most critical period in an applications life cycle is not so much its infancy as its adolescence.
Before release the customer accepts bugs. Milestone deadlines are MS Project phenomena.
After release the nice customer is replaced by angry users. Deadlines? Yesterday.
Before release you have whiteboard meetings, cookies and pleasantries.
After release you get nasty phone calls and late nights at work.
The truth is: after release is where the design will be tested and where the difficult redesign will occur.
Is this, the period between release and maturity, where you need team discipline more than ever? Is this where you need experienced people who understand the applications original design and goals?
I think so.
At release the application isn’t “done”, it just got started.