Monthly Archives: April 2013

Brook’s law, why software engineering is not programming

Part 2 of Managing Software Projects

Do you know the difference between programming and software engineering?

Not a Jeopardy question, the difference affects tens of millions of people who work directly on software. Programming is writing instructions for a computer, something everyone should learn. Software engineering occurs when two or more people work on a project, which introduces a major difference: communication. Communication is also something everyone should learn. Writing good instructions is clearly important but the communication between two or ten or a hundred programmers quickly becomes the critical factor in producing a good product.

No it's this way

The important thing to know here is Brooks’ law. Fred Brooks ran software development for IBM during the 60s and 70s; thousands of smart people writing millions of lines of code. For large projects like operating systems he tried to scale up by adding more programmers, just as a construction project would add more workers or a factory would add more assembly lines. But it didn’t work.  He concluded that the more programmers he added the slower things went.

Brooks formulated his law of communication as “adding programmers to a late project makes it later.”

Here is the problem. For every programmer there is a communication link between them and every other programmer working on the project or n(n-1)/2 links. For two programmers you have one communication link; three, three links. So far, not so bad, sit those three people in the same room and they might avoid too many misunderstandings. Keep going up, with seven programmers you’ve got 21 links, about half of everyone’s time is spent coordinating with others. A sixteen programmer team? 256 links!

Clearly the project cannot be built in half the time by doubling the number of workers.

Very quickly the number of communication paths increases faster than the number of programmers,  Worse it’s not just programmers, it’s everyone who needs to intimately know the software: QA staff, the development manager, the product manager. This limits the number of people who can work on a single project.

bricks_smallBut wait, plenty of companies employ thousands of programmers, how does Lockheed Martin build something like an artillery targeting system for the army?  One piece at a time, with vast amounts of planning, hundreds of people dedicated to project communication, working for decades and probably 100% over budget. Much of this effort goes into splitting the project into pieces that a small team can handle and defining detailed interfaces to minimize the communication they need to do with each other.

So that’s the difference, communication is the key skill of software engineering. Software engineers are often not known for their communication skills – or maybe we should say programmers are not known for their communication skills but a well-functioning software engineering team is one that communicates well.