Developing software costs money so it's important to make sure everyone on your team is moving towards a clear, shared goal to avoid wasted effort. There are many approaches to achieving your goal, and over the course of the last 20 years the software industry has seen them all.

Having spent a year researching Agile development (Scrum), followed by a year using it, I've seen the results of this approach first hand. In short, when you couple experience with a simple approach to estimation and tracking and add a capable Scrum master to manage impediments, your chances of successfully guiding a team to a goal, on schedule are very good.

You may have noticed the word 'experience' above is emphasized. This is very deliberate because this is where agile development (and Scrum) breaks down, and this is why agile can be the wrong choice when developing certain types of iPhone apps.

So what is it about certain types of iPhone apps (and a certain level of experience) that makes Agile the wrong choice?

Two things.

1. Often the goal of your team will be to add some magic to your iPhone app. This might be a 60 fps Doom renderer. Even with a well written spec, the actual final details of this magic may be unknown until well into the project. This may be because without prior experience writing an app just like the one you're working on, research is required. The results of research (and time required) are very, very difficult to estimate.

2. Some types of software development (like server side development) generally consist of well defined goals. The server receives A, stores B and returns C. An experienced developer can take this spec and provide a good task break down with estimates that will likely hold true. With most of the iPhone apps we've worked on, the same type of spec is usually present, with one added requirement. Quality. Achieving the required quality level usually means iterating over a project until a general consensus deems the app at a quality level ready for launch.

Point 2 could mean putting a beta in the hands of a sample audience and then responding to comments and requests that could dramatically increase the quality of you app. This is also very difficult to estimate and could mean a significant re-write if the quality of your app is of the utmost importance. 

Having said all of this, it is possible to use Agile to a high degree, when developing high quality iPhone apps.  For 3D Bookshelf, we identified the areas requiring research and scheduled them up front. This takes point 1 out of the equation. We accepted that we would spend a certain amount of time researching our options. This involved the production of a proof of concept prototype. We didn't know how long this would take. To keep things real, we did put a limit on the amount of time we could invest in this stage of the project. In the end, we got through it much quicker than anticipated, but we couldn't have known that in advance. With that out of the way, most of the rest of the project became very straight-forward to estimate and schedule.

Agile developers reading this are probably thinking, hold on, if you've put a time limit on the research task, surely this fits with Agile or Scrum. The answer is no. The results at the end of this stage could have an explosive effect on the rest of the project. For example, we could have tried to produce 3d Model content for the 3D Book system (and a lot of it) before we found out that it was much much simpler to produce a real-time engine to create the 3D Books. That's potentially a lot of wasted effort both in terms of management and content production.

There are other aspects to this project that were inherently suited to Agile development. These included the Twitter competition service, the web site and preparation of most of the content and tool updates.

The last few weeks were set aside for polish. That's where we are right now. We've said goodbye to schedules. That takes care of point 2. We're no longer trying to track this using Agile techniques. We know we're close to the end of the project. We know we can get to a quality level we'll be happy to release at. When will that be? We don't know yet.

Again, to be realistic we have set a limit to this. We can't throw infinite time at the project and expect to make any kind of financial return.  All I can say is we'll release between now and that cut-off date.

We've successfully applied the approach above before, to a previous iPhone project (a custom app for a high profile UK artist). Based on some initial research we produced a sprint task breakdown that came to 120 man hours. These tasks were completed in 131 man hours, only 11 hours over the estimate. Not bad considering the research involved (an advanced OpenGL renderer) and change requests. In the end we added a further 20 hours of polish at the request of our client. At all points in the project we had a good clear understanding of where we were in terms of the overall schedule.

Conclusion

Agile software development becomes quite powerful when it is coupled with experience and familiarity with the project domain. This is the guide we use for deciding when, and when not to use it.

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