Smart Process Design

I just finished reading the anniversary edition of The Mythical Man-Month: Essays on Software Engineering by Frederick P. Brooks Jr., a classic on the difficulties of project management in the software engineering industry. It’s one of those great books that makes you step back and think things through from a new perspective. A few short notes follow, where I drew an analogy to the over-budget experiences in process engineering and just managing large projects in general.

The book was written in 1975 as a from-the-trenches meditation on the hazards of managing huge software engineering projects. For example, writing operating systems. Although the book deals with software engineering, and some of the challenges described are long-gone due to advances in technology, there is still some wisdom in the book that causes it to be read to this day. And Brook is a good writer: frank, wide-ranging in interests and quotations, practical, and interesting. It’s one of those “work books” that you won’t mind reading in your spare time.

Brooks’ Law: Adding Manpower to a Late Project Will Only Make it Later

This is one of the core ideas of the book, so let’s step back and understand it. First, Brooks points out that large projects grow exponentially harder as they grow larger. One of the reasons is the inter-communication factor: it becomes harder and harder to keep large groups of people aligned, and allow their pieces of work to link up.

Some work, like picking cotton or sewing shirts, does not have this problem. In such jobs, people can work independently and with minimal interaction. Adding more people does not add to the communication burden, so you can always add people onto a job to reduce the time it takes. Men and months are interchangeable: add more of one to reduce the other.

But in software engineering (and many modern projects) you need people communicating, because their changes can directly impact on or interface with the work of other people.

If each part of the task must be separately coordinated with each other part the effort increases as n(n-1)/2. Three workers require three times as much pairwise intercommunication as two; four require six times as much as two. If, moreover, there need to be conferences among three, four, etc. workers to resolve things jointly, matters get worse yet.

This can lead to perverse outcomes. For example, suppose a project is estimated to take 12 man-months of effort, and the deadline is in four months. So you hire 3 people, and divide the project into four “stages” or “milestones,” with each stage taking a month for your team to complete. (3 people * 1 month = 3 man-months effort / month time elapsed. One quarter of 12 man-months of work is 3 man-months of effort). But say you under-estimated the first stage and it takes two months. Now what?

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