July 2009

The essence of Lean software development

Derivation of the essential development workflow by induction

1.  Imagine that you have produced a high-integrity, high-capability design that is suitable for your problem domain.  The design is of high quality in every way that matters to you:  reliability, usability, security, response time, power consumption, whatever.  You have reliable metrics to assess all of your relevant quality attributes.  It does not matter how you created this design. It could be a rigid phase/gate process, it could be a million monkeys.  It only matters that you are in possession of such a design.

2.  Starting with your finished and delivered system, add one feature or improve one performance specification in a way that preserves all of the quality attributes that you could measure in the original system, plus any new attributes that are relevant to your change. Deploy the newly enhanced system and validate.  This is your essential development workflow.

3.  Repeat step 1, but with one fewer initial feature, or one relaxed performance attribute.

Any sequential development workflow can be pipelined

1.  Take all of the steps from your essential development workflow and arrange them in dependency order.  Work serially through the steps until a result is produced.  If the result is not satisfactory, then repeat the process and apply what you have learned until a satisfactory result is produced.  It does not matter if this process is not efficient.

2.  Allocate sufficient resources so that two such design increments, following the essential workflow, can execute in parallel without overlapping resources.  Create a build/integration process that allows each feature to develop in isolation and integrate through to deployment and validation.  Integrations will necessarily be serialized, creating a pipeline.  This is your essential development process.

3.  Map the value stream of your development process.  Add sufficient capacity to each pipeline to realize flow. Add or remove stages to the pipeline to reduce backflows or otherwise reduce cycle time.  Substitute new practices or stages as the situation demands and capability allows.  Find bottlenecks and relieve them.  Share resources between pipelines to improve utilization.  Add or remove pipelines as necessary to match demand.

4.  Repeat step 3, forever.

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A swimlane for ad-hoc workflow

Swimlanes are used to track parallel work streams within a common resource.  The most typical use might be grouping composite work items with a parent.  Another typical use is an expedited lane for emergency work items that can skip queues and preempt other work.  Swimlanes generally indicate some kind of branching.  That can be either work item branching or workflow branching.

Kanban systems can be used when the work generally follows some kind of common workflow.  For many software development projects, this is an easy constraint.  Most software involves some kind of problem definition, some kind of design activity, and some kind of verification.  Most software development also involves the use of a limited set of technology applied to a limited set of systems within a limited problem domain, so that most of the work done falls into a few general types.

Most is not all, however, and sometimes work will appear that doesn’t fit neatly into any well-defined type.  Or maybe it does have a type that we haven’t defined yet.  If the work is non-value-added, we can chalk it up to overhead.  If the work is value-added, we will want to track it like all of the other value-added work.  A useful trick for managing that kind of work is to reserve a swimlane for ad-hoc workflow:

adhoc_swimlane

If you find yourself using the ad-hoc swimlane frequently, you might want to map the value stream of some of the work items to see if you can discover some latent or emerging workflow.

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