What's the key to team and individual developer productivity in maintaining and extending a large application? Let's start by making the following assertions:

• A developer's knowledge of an application code base is likely the single biggest factor of individual productivity.
• Correspondingly, the team's collective knowledge of an application code base is the single biggest factor of team productivity.

Reflecting on it a bit, it doesn't take a rocket scientist to test the validity of these statements. Any real-world, modestly capable application runs to tens of thousands of lines of code, has more than a handful of developers, and is developed over months if not years.

Pondering the reasons for a team's productivity or lack thereof, you will likely come up with a number of answers: knowledge of the APIs, libraries, frameworks, and programming language; knowledge of the application domain, effective tools, development processes, continuous builds, unit tests, and so on.

But, over and above all of this, individual productivity is directly proportional to knowledge of the code base and the team's productivity is directly proportional to the team's collective knowledge of the code base.

Productivity's dependence on code base knowledge grows rapidly as the code base grows larger, teams become bigger, and the code ages.

The collective knowledge of the code base is a critical factor, and hence should be considered a critical asset.

Today, a team's "collective knowledge" is not really collective because critical pieces of information may reside with only one or two individuals for a specific feature area. Today's productivity concerns are due to the pain involved in individuals needing to come up to speed on some part of the application where there is limited understanding. Even modest employee turnover can open up critical gaps and affect the team's ability to maintain or extend an application. In this sense, lower productivity means more than just taking an extra day or two to complete a task.

The Application Factories' vision addresses this missing link in the development productivity tool chain.