During recent discussions with XP folks on the topic of Kanban, it occurred to me that based on my understanding, XP can be described in terms of a Kanban System for Software Development. This is an attempt to do that, on the basis that it might be useful in helping teams understand Kanban concepts. I have structured the description around the five primary practices of Kanban that I have previously blogged about.
1. Mapping the Value Stream
Here’s an example of an XP Value stream
- A customer comes to the team with a problem they want solving, and collaboratively they write a set of User Stories
- The team then holds an Iteration Planning meeting to prioritise which User Stories they believe they can deliver within the next iteration (which is 2 weeks in this example)
- The team then pick the first of those User Stories, and plans how they will build it.
- They build a User Story (using good engineering practices)
- When the team has something to show, they review progress with the customer. In this case, every 2 days on average. I assume that the team will be collaborating with the customer more often than that, but am not showing that level of feedback for simplicity. Reviewing a User Story may result in re-planning and re-building (iterating). Completing a User Story will trigger another User Story being planned and built.
- At the end of the Iteration, the customer accepts all the completed User Stories. At this point the User Stories are re-prioritised again and another set chosen for the next Iteration.
- At the end of the Iteration, the software may also be released, and more User Stories may be written.
In practice, the workflow is not this precise, but I think its a close enough approximation. For example, new User Stories could be written at any point.
2. Visualising the Value Stream
An XP teams may use a very simple visualisation such as the one above, which focuses on the Plan-Build-Review section of the Value Stream. The User Stories (yellow) chosen for an Iteration are initially not started. When they are planned, then tasks (grey) are added, and the tasks are working on until they are all done, and the User Story is Done.
3. Limiting Work in Progress
An XP team will limit work in progress by working in pairs, with each pair only working on a single User Story at a time until it is Done. Thus in the above example, a team of four developers limits work in progress to two User Stories by two pairs.
4. Establishing a Cadence
XP teams have a very specific and synchronised cadence which is created by time-boxing the Iteration. Prioritisation, Reviews, Retrospection and Releases all occur at the same time interval, and User Stories are planned to be completed within that time interval.
5. Reducing the Kanban Tokens
An XP team is always striving to improve, usually by using retrospectives. As such, in the above example, they may reach a point where all four developers are able to work on the same User Story, and as a result complete it sooner.
Assuming that this description of an XP based Kanban System is not widely off the mark, I hope that it serves to communicate that XP and Kanban are not alternatives, but different and compatible ways of describing a process. Further, I have found that by understanding a process in terms of a Kanban System, it has helped my think about alternative ways of evolving that process in order to improve it. There is of course, more to XP than I have mentioned here, such as release planning, and the usual good engineering practices.