Monday, January 5, 2015

Discussing "Inventory" in Software Development - Classifying approaches


Interesting comments of Martin Fowler starting from this idea : "So as an example - one of the principles of lean manufacturing is the elimination of inventory.This leads to the question of whether there is an analogous item to inventory in software development."

http://martinfowler.com/bliki/MetaphoricQuestioning.html

Martin Fowler make a very interesting comment about a IMO less interesting idea "up front documentation is the equivalent of inventory": "Now I agree we need to substantially reduce this kind of speculative documentation; but the rationale for doing so must come from thinking about the software development process, not from purely reasoning by analogy."

Here is my comments on these subjects.

Manufacturing-Software Development Analogies

We should be careful on these analogies because these domains areas are pretty different. Examples: Just-In-Time approach in manufacturing must find solutions for a JIT Production (where the design was previously done "offline") and software development must find find solutions for a JIT Design ("Code is design").

Inventory in Software Development 

Manufacturing inventory mean (simplified) a reserve queue of (done) products, ready to be sold. A similar concept in software development IMO is not the massive up-front documentation (based on too many assumptions) , but rather in the motive of producing a such documentation: a massive set of requirements allocated to the same release/delivery/project. "No inventory" approach means as small is possible set of requirements per release. Indeed from this point of view, the classification is already done:
  • Large set of requirements releases - non-agile, non-lean approach
  • Small set of requirements releases - Agile approach, Lean approach
  • Very small set Small set of requirements releases - Continuous Delivery approach
An explicit description of  lean and Agile life-cycle models could be found in DAD- Disciplined Agile Delivery: https://disciplinedagiledelivery.wordpress.com/lifecycle/ 

More: With an increased construction productivity and/or a higher envisioning productivity, a larger set of requirements could be delivered in the same time. Productivity suppose here here good results and quality 

The resulted formula of "Inventory" for software development:

(Set of Requirements "volume")/productivity.

Comment: the "formula" could be enhanced to:

 (Work volume")/productivity. 

But, in this case, it is too vague.  The main aspects that increase volume or complexity of the "work" must be specified. here are some of them:
  • Requirements volume and complexity at the start
  • Solution that must match the requirement 
  • Team productivity 
  • Process
All elements of the formula are "requirements" for "No Inventory" process in software development:
  • small set of requirements
  • good design
  • no junk stories with associated phantom features
  • high productivity (all contributing aspects)
  • small releases 
  • adapted/effective/efficient process 
Finally, seems that starting with this assumption about a "No Inventory" approach for software development we are very close to the description of a Lean/Agile approach.

See more here:

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