# Tuesday, 20 October 2009

Think big; act small; fail fast; learn rapidly.

These are some of the lessons from Tom and Mary Poppendieck’s book Lean Software Development – An Agile Toolkit.

The Poppendiecks take what they learned from Lean Manufacturing (many of which were originated with the pioneering work of Toyota Motor Company) and apply these lessons to software development.

They deliver advice in the form of 22 “tools” that can make a team or project more lean. Related tools are grouped together into chapters.

The authors recommend that organizations define, find and eliminate waste wherever it occurs in a process. Examples of waste in software development include defects, waiting, extra features or processes, and any non-essential activity. To assist finding waste, they recommend Value Stream Mapping - a technique in which one lists in sequences all the steps from customer request to delivery and estimates the time to completion of each step and the wait time between each step. This technique often makes bottlenecks obvious so that they can be reduced or eliminated.

Many of the tools in this book overlap. For example, iterations and feedback are listed as separate tools, but shorter iterations allow for more frequent feedback to the development team. Short iterations also expose design problems more quickly sot that the can be corrected early in the development cycle at a lower cost.

Much of the authors’ advice seems counter-intuitive. For example, they recommend against detailed planning at the start of a project and attempting to optimize every part of a multi-part project.

A popular approach among software project managers is to create in advance a detailed plan of every step in the design, development and deployment process and to estimate each step. To do so, you need to know a specific scope of everything you will build. This makes sense as a risk-reduction strategy, until you consider that environments, requirements, priorities and people often change while software is being developed. A rigid plan created up front often requires an aggressive change control process to alter that plan in any way. And for long-term projects, the changing landscape almost always forces changes to the design. Also, when users know they will only get one chance to request features, they tend to ask for far more, so scope tends to get bloated when projects are planned in this way. A better approach is to re-evaluate priorities periodically throughout the development process and keep focused on the top priority features that have not yet been implemented.

Complex project can and often should be split into a number of smaller phases or tasks. This helps to simplify the complexity. Many managers then strive to optimize each phase of the project, assuming that this goal will lead to overall optimization of the project. The Poppendiecks advise against this goal because optimizing some phases may cause a bottleneck in your overall project, thus slowing down the project as a whole. A buildup of code waiting to be tested, for example, represents waste that should be eliminated. It is best to look at the system as a whole when setting optimization goals. Optimizing each part ignores the interaction between these parts.

The book finishes with practical advice to get started making your team and process more lean.

Lean Software Development - An Agile Toolkit is a clearly-written, thoughtful book and anyone involved in software development projects can benefit from reading it.

Agile | Books