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Applying Little's fLaw to Software Development



Concept of Product Development Flow
"I believe that the dominant paradigm for managing product development is fundamentally wrong.  Not just a little wrong, but wrong to its very core.  It is as wrong as we were in manufacturing, before the Japanese unlocked the secret of lean manufacturing.  I believe that a  new paradigm is emerging, one that challenges the current orthodoxy of product development."  -- Donald Reinertsen
Reinertsen goes beyond the advance ideas of lean manufacturing, what he calls Flow-Based Product Development.

Scrum was sparked by a paper called The New New Product Development Game by Hirotaka Takeuchi and Ikujiro Nonaka (1986).  Are you seeing a synergy of ideas?


Lean principle of Flow

In the manufacturing world Toyota exemplifies the achievements one may obtain in 50 years of practicing a new mindset of principles.  Manufacturing deals with repetitive tasks predictable processes to produce component parts, homogeneous delay cost, and homogeneous task duration to produce components and in assembly of components into consumer goods.  These product manufacturing sequences work fine in a FIFO order, which are quite acceptable in manufacturing goods.  However this is untrue for Flow-Base Product Development.  Because this type of development deals with non repetitive, highly variable, flow of dissimilar components.

What is a good tool in manufacturing is not necessarily a great tool in Product Development.

Application of Little's Law


 -- by Mark Woepple.


Constraints implicit in Little's Law

a) it is dealing with averages; for averages to apply to a domain, there needs to be more than a few things to be measuring - and those items should exhibit a general resemblance to a bell curve, for which an average is a significantly useful characterization.

b) this law - which Little describes as is a mathematical theorem and therefore a tautology, applies to queues.

c) when giving examples for the application of his Law (theorem) Little and Graves does not use a queue for any truly creative endeavors - such as mass production of unique art works, or the building of architecture significant unique structures (bridges, towers), etc.  What is described are: Semiconductor Factory, E-Mail tools, Hospital Wards, TollBooths, Housing Market, and Doughnut Shop.

d) this law was derived from a study of steady-state processes. "So far we have developed and discussed Little's Law as a relationship among steady-state stochastic processes. The contexts we have examined have been well- behaved, stable, and on-going. In particular we assume that the characteristics of the arrival and service processes are stationary over time."  It is generalized beyond that domain.

e) in application to a variant system (grocery story) the analytic interlude was conceived; requiring two essential conditions:

  • Boundary conditions-we specify the finite time window to start and end with an empty system. This was a natural condition for the supermarket, and indeed, would be common for many service systems. 
  • Conservation of customers-we assume that all arriving customers will eventu- ally complete service and exit from the system; there are no lost customers, so that the number of arrivals equals the number of departures. Again, this is a valid assumption for many systems of interest.  

"Notice that our formula is exact, but after the fact. In other words, we cannot complete our calculation until the supermarket door shuts. This is not a complaint. It merely says that we are observing and measuring not forecasting."

f) when transmuting Little's Law to Operations Management the transmuted equation becomes THroughput = Work In Process / CycleTime ::  TH = WIP/CT
"At a minimum we must have conservation of flow. Thus, the average output or departure rate (TH) equals the average input or arrival rate (A). Furthermore, we need to assume that all jobs that enter the shop will eventually be completed and will exit the shop; there are no jobs that get lost or never depart from the shop. In addition, we need some notion of system stability. We consider two possibilities, as this issue raises another important consideration."
g) concluding remarks for Operations Management application:
"In each case we see that Little's Law can apply, albeit with some required conditions and thoughtful attention to the goals of the application."

Applying Little's fLaw to Software Development


LKCE12: Daniel Vacanti - Little’s Flaw





See Also:
Chapter 5 Little's Law - MIT by Little & Graves

The average waiting time and the average number of items waiting for..a service in a service system are important measurements for a manager. Little's Law relates these two metrics via the average rate of arrivals to the system. Thisfunda- mental law has found numerous uses in operations management and managerial decision making. 

When U.S. air force discovered the flaw of averages
In the early 1950s, a young lieutenant realized the fatal flaw in the cockpit design of U.S. air force jets. Todd Rose explains in an excerpt from his book, The End of Average.

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