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2.2 Process Models 31

the abstraction level of an existing model. Unfortunately, questions may emerge
at different levels of granularity.
These are just some of the problems organizations face when making models by
hand. Only experienced designers and analysts can make models that have a good
predictive value and can be used as a starting point for a (re)implementation or
redesign. An inadequate model can lead to wrong conclusions. Therefore, we advo-
cate the use of event data. Process mining allows for the extraction of models based
on facts. Moreover, process mining does not aim at creating a single model of the
process. Instead, it provides various views on the same reality at different abstrac-
tion levels. For example, users can decide to look at the most frequent behavior to
get a simple model (“80% model”). However, they can also inspect the full behavior
by deriving the “100% model” covering all cases observed. Similarly, abstraction
levels can be varied to create different views. Process mining can also reveal that
people in organizations do not function as “machines”. On the one hand, it may be
shown that all kinds of inefficiencies take place. On the other hand, process mining
can also visualize the remarkable flexibility of some workers to deal with problems
and varying workloads.

2.2 Process Models

It is not easy to make good process models. Yet, they are important. Fortunately, pro-
cess mining can facilitate the construction of better models in less time. Process dis-
covery algorithms like the α-algorithm can automatically generate a process model.
As indicated in Chap. 1, various process modeling notations exist. Sometimes the
plethora of notations is referred to as the new “tower of Babel”. Therefore, we de-
scribe only some basic notations. This section does not aim to provide a complete
overview of existing process modeling notations. We just introduce the notations
that we will use in the remainder. We would like to stress that it is relatively easy
to automatically translate process mining results into the desired notation. For ex-
ample, although the α-algorithm produces a Petri net, it is easy to convert the result
into a BPMN model, BPEL model, or UML Activity Diagram. Again we refer to
the systematic comparisons in the context of the Workflow Patterns Initiative [101,
130] for details.
In this section, we focus on the control-flow perspective of processes. We assume
that there is a set of activity labels A . The goal of a process model is to decide
which activities need to be executed and in what order. Activities can be executed
sequentially, activities can be optional or concurrent, and the repeated execution of
the same activity may be possible.

2.2.1 Transition Systems

The most basic process modeling notation is a transition system. A transition system
consists of states and transitions. Figure 2.1 shows a transition system consisting of