Beyond the Limits of One-Dimensional Lists
Prioritizing requirements for a software release is an activity which frequently crosses the border between science and psychology. The goal is to determine the right set of things to do for a release. For many IT projects this turns out to be a moving target.
In software product development, requirement priorities are set by the product manager. Typically a product manager focuses exclusively on the market need of a requirement and its selling potential. Excellent software companies look at additional factors as well:
- Cost
- Risk
- Fit to product strategy and architecture
- Ability to deliver
Creating estimates for these factors cannot be done by a single person. Experts from different domains are needed.
There is a couple of techniques available to cope with this issue. Most of them are based on “cost-value” approaches. In my projects, I have applied a variety of them ranging from simple to complex ones. Often we started with something similar to Karl Wieger’s requirements prioritization approach (see www.processimpact.com).
Ultimately, these techniques yield a list of requirements ordered by their relative priority. Such a list is charming because you can always pick the most important requirement next. It is so charming, that this approach has made it into today’s most prominent development approach: Agile methodologies. In agile projects, the term “product backlog” describes a priority-ordered list of work items, which are addressed from top to bottom.
However, there are some shortcomings with these approaches, which need to be overcome in industrial practice. The key problem is the underlying assumption that requirements can be prioritized independently from each other.
Experience shows that this is seldom the case. Most requirements are interdependent from other requirements.
Across many industry domains including software and IT, the fundamental approach to building a system is always the same: A high-level plan is decomposed until the units of work are manageable. Elements of such units share some characteristics. They belong to the same domain and have similar complexity. Rating such elements in relative order works well. However, if the elements are from different domains, you may run into problems: They might have architectural dependencies which cannot be addressed in isolation. Many times, I saw projects getting stuck, because one team was waiting for something that another team had decided to lower in priority.
This problem of deadlock situations can be addressed by explicit dependency management. In requirements engineering, the concept of traceability is used to manage dependent work-items. Directional links express dependency relationships. These techniques exist and are available in most modern requirements management tools. However, in practice, these solutions can be very hard to accomplish, because they require more discipline than most projects are able to bring up.
So I recommend to deploy lightweight traceability using tagging mechanisms at requirements. Sometimes multiple backlogs are used. Each backlog holds items from the same domain. I have seen such approaches working pretty well in many project situations. So they might be the optimal solutions with the right mix of rigor and flexibility.
And don’t forget the importance of communication: Whatever approach one uses, it will be successful only if it is accompanied by good communication structures in the organization.