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design phase, a formal version of the model can be used to confi gure a workfl ow manage-
ment system. One of the functions of such a system is that it can allocate activity instances
to the workers in that process at run-time (Jablonski & Bussler, 1996; Van der Aalst &
Van Hee, 2002). However central the activity concept may be within such a setting, it is
the author's experience in various workfl ow projects (De Crom & Reijers, 2001; Reijers,
2003) that the knowledge of identifying activities within a business process is limited and
can result in ill-defi ned activities.
The results of ill-defi ned activities on the operational performance of a process may
be substantial. One may think of activities that are needlessly small. This increases the
number of hand-offs between activities, with a corresponding increase of errors (Seidmann
& Sundararajan, 1997). Activities that are too large may cause infl exibility within a business
process, since its underlying operations must be performed regardless of their merits under
the circumstances (Van der Aalst, 2000).
The aim of this chapter is to provide some tangible guidance for activity defi nition
in the form of a heuristic, by making the intuitively appealing notion of a 'logical unit of
work' operational. The application area is the design of workfl ow processes. The heuristic
we propose is based upon a cohesion metric for activities, as inspired by similar notions
in software engineering. In this way, insights from computer science are transferred to the
business area, which in this case seems to be a successful undertaking.
The structure of this chapter is as follows. First, we will introduce some basic concepts
and give a short overview of existing activity defi nition heuristics in the workfl ow manage-
ment fi eld. Next, we will present the cohesion notion we mentioned earlier, as well as a
heuristic for its use. After its introduction and the presentation of some examples, we will
subject the cohesion notion to both a theoretical and empirical evaluation. Some concluding
remarks and directions for further research form the fi nal part of this chapter.
ACTIVITY DESIGN IN
WORKFLOW MANAGEMENT
Terminology
An activity is a specifi cation of a part of work to be accomplished. We use 'workfl ow
process' as a synonym for a specifi c type of business process. A business process itself
is a conceptual way of organizing work and resources by distinguishing a set of related
activities. Workfl ow processes are usually found in administrative contexts (e.g., banking,
insurance, government, etc.). They are particularly suitable to be supported by workfl ow
management systems.
Each single activity that is distinguished within a workfl ow process may be divided
into a number of operations. Operations are used to identify small parts of work in a way
that is still useful within the business context. In general, it is also possible to distinguish
an activity without mentioning the operations it comprises (non-determinism).
We interpret the matter of activity defi nition as the formulation of a goal and/or the
assignment of operations to an activity within the context of a single workfl ow process.
Part of the work in defi ning activities involves an evaluation of its properties, such as its
size, its workability, its performance, etc. Although a broader view on an activity defi nition
may also include matters such as the development of work instructions, various views and
