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Critical difference between software development and construction...
Submitted by regen_r8 on Sat, 2007-02-10 09:31.
estimation | velocity
Glen Alleman from the Herding Cats
blog offers this
post on the subject. I want to agree with him.
I merely need to remind him that there is one key difference
in the two industries:
Estimation - my experience with software development, and construction projects (church, home) though small, informs me of a key difference. In construction projects, Once the required work is known, it can be estimated with some reasonable accuracy, because the vast majority of construction tasks have been done exactly the same way by the people who are doing them. The tool set doesn't change every 2-5 years. Carpenters still use nails to fasten wood together. Wood still has the same physical properties that it did in 1965. In software, there is a programming language every 6 weeks, and every 10-20 years the nature of raw materials change - assembler to procedural to functional to 4gl to object oriented, etc. The new raw materials and tools require estimation to be redone from scratch. The other factor in estimation is the difference in productivity between master, journeyman, and apprentice practitioners. In construction the difference between resources can be a factor of 2 or 3, but years of stable estimates for building 40 linear feet of stud wall, provide a rational basis for scheduling. In the software industry, only the practitioner who is doing the work can estimate his or her rate of completion, and the difference between practitioners can be a factor of 10 or 20.
When I hear that project management is different between construction and software development, this is the only difference that I think is real. For me, it is the reason that short iterations are important, so that I can measure the output of each practitioner against their estimates. That way I can predict velocity or rate of completion. In software development, that is the only way that I have found that works to manage the schedule, because estimates are highly individualized.
In construction, the schedule challenges revolve around different sets of constraints: availability of resources, availability of raw materials, weather, and unanticipated work. Software projects, thankfully, avoid the complexity of weather.
Estimation - my experience with software development, and construction projects (church, home) though small, informs me of a key difference. In construction projects, Once the required work is known, it can be estimated with some reasonable accuracy, because the vast majority of construction tasks have been done exactly the same way by the people who are doing them. The tool set doesn't change every 2-5 years. Carpenters still use nails to fasten wood together. Wood still has the same physical properties that it did in 1965. In software, there is a programming language every 6 weeks, and every 10-20 years the nature of raw materials change - assembler to procedural to functional to 4gl to object oriented, etc. The new raw materials and tools require estimation to be redone from scratch. The other factor in estimation is the difference in productivity between master, journeyman, and apprentice practitioners. In construction the difference between resources can be a factor of 2 or 3, but years of stable estimates for building 40 linear feet of stud wall, provide a rational basis for scheduling. In the software industry, only the practitioner who is doing the work can estimate his or her rate of completion, and the difference between practitioners can be a factor of 10 or 20.
When I hear that project management is different between construction and software development, this is the only difference that I think is real. For me, it is the reason that short iterations are important, so that I can measure the output of each practitioner against their estimates. That way I can predict velocity or rate of completion. In software development, that is the only way that I have found that works to manage the schedule, because estimates are highly individualized.
In construction, the schedule challenges revolve around different sets of constraints: availability of resources, availability of raw materials, weather, and unanticipated work. Software projects, thankfully, avoid the complexity of weather.