Activity Level and Decomposition

One of the powerful benefits of a process diagram is in its ease of use. There will generally be some set of bubbles or boxes that represent an activity, connect by arrows the show the flow of information and material. Most stakeholders can read such a diagram and quickly grasp the message it conveys.

But most organizational problems are wider ranging and impact an organization both in breadth and depth. There is more to them than can fit on a single activity diagram. So how do we deal with this complexity of volume? Process modeling give us a useful approach: decomposition, the breaking down of one activity into many component activities.

When we decompose a process or activity, we break it down into sub-processes or procedural steps. We do this to reduce complexity of presentation. We then will have multiple diagrams that present information, logically arranged and structured so that the relationship amongst the diagrams is clear.

So far so good, as most analysts will have no difficulty with these ideas. The toughest challenges come in two different areas: understanding atomic activities and selecting a decomposition strategy.

Lets discuss decomposition strategies first. The best way to break down a big activity into smaller ones is to understand actors and activity streams. Typically an organization process is in place to bring about some result: student registration, new member enrollment, changing employment status, producing a detail component, and others. When the material or information is acted upon a different person or machine, then there likely is an excellent spot to separate component activities. In a machine shop this might occur when an unfinished detail part must be move from, say, a machine that cuts to one that drills holes. In a hospital, this might occur when an ER triage specialist assigns a patient over to a surgeon. In both cases actors change during the course of an activity stream; for the former example, the activity might be called "produce detail part", the latter might be "treat emergency patient".

There are numerous other approaches to decomposition. At higher levels it might make sense to decompose by geography, i.e., where something happens. Or it may be by organizational function, as in accounting versus finance versus marketing. Or it may be structural, as in holding company and its subsidiaries. The analyst will likely find it useful to keep an idea of size and level of a complete enterprise activity model will look like, while beginning to create the process model.

Activity atomicity is the idea of knowing when to stop decomposing. I find it useful to think of elemental or atomic activities as being those that are irreducible in the sense that a stable product or deliverable could be passed along as a meaningful unit. For instance, in the detail shop example above, using a single machine might be thought of as atomic. And in the ER example, completing admission, triage and initial treatment might be three different atomic activities. Naturally it is possible to decompose further, but it is not useful in generally describing the activity. Further decomposition might well be said to be about "how" no longer "what". For this the best approach might be procedure steps, also know as use cases.

When I review elemental activities, I often use an analogy form chemistry: elemental processes are like molecules while a procedure step is more like an atom.