A software development lifecycle that does not include design review early in the process is doomed to poor estimates, cost overruns, and a wildly inaccurate schedule.
Why? Let me tell you what just happened to me.
I picked up a task for a project manager because I had some time free and his resources were completely booked. It was a simple feature with a two day estimate and it was already scheduled for release without having gone through design review. Since it was scheduled, it had a code cutoff date. That was last Friday.
The feature was pretty easy to implement. I needed to add a column to a database table, add support for it in our system, create some services (as in SOA) to change this field, and include the field in our web UI. That’s it. One database column with support for it across our system. Not a hard task.
I implemented the feature within the original estimate, I checked my code into our version control system, signed off on the feature, and asked our Database Engineers (DBEs) to include the new column in our test environment. As far as I know, this was the first time a DBE had a chance to review the feature. They put my change on hold while they suggested moving the field to a different table.
The DBE has a good argument for the field being on the other database table. He may be right. The original requirements may have been good but not good enough. But the problem is this review happened after the entire implementation was said and done.
Changing where the column exists represents a 3X cost of the original feature. The first 1X was the original implementation. Should we choose to move the column, I have to undo the original work and then do it all over again for a different table. Even if undoing the original work isn’t a full X of cost, it is still work I have to do that was not part of the original estimate. Redoing all the work on the new table is a full X of additional cost. We’re at least 2X above the estimate.
A 30 minute design review with the appropriate people would have kept the cost to 1X and given us the right solution the first time. Instead, we’ve got a potentially sub-optimal 1X solution or a 3X correct solution. And this was a simple feature. Larger features with more complex requirements would incur significantly higher cost overruns if not properly designed up front.
Design reviews must be an early part of the process, not an afterthought. It is the only way to avoid 3X overruns.