PHOTOOG Photography writings by Olivier Giroux


Summary: A Model of Large Program Development (part 3 of 3)

See part 1 here, and part 2 here.

Fault Model

Two models are presented: one where fault generation is proportional to effort alone and one where it is also proportional to size. The first model applies best during the development of the project, and allows one to make predictions concerning growth, and the second applies best at the time of project death and serves to predict it.

Model #1


  1. h is the personnel invested in activity P.
  2. r is the number of faults in the system.
  3. m is the size of the system.
  4. F is the rate of addition of faults per manpower spent.
  5. R is the amount of manpower needed to remove a fault unit.
  6. E is the amount of manpower needed to grow by one unit.


Growth is linear in manpower and appears unlimited. Under this regime the system grow very quickly if fault generation is low.

Model #2


  1. D is the rate of additional fault generation due to system size.


The critical mass of the system, the asymptotic size at which it implodes, is proportional to manpower. A sudden reduction of manpower can cause a seemingly fine system to implode suddenly if all other parameters remain the same.

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