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176 M. Pesic

high

groupware flexibility support procedural workflow management systems

low

control

users system

Fig. 6.1 Flexibility vs. support, adapted from [79]

innovative research prototypes, few of the research ideas have been adopted in com-
mercial systems. This is the reason why there is a question mark in the middle of
Fig. 6.1.
This chapter presents a completely new way of looking at workflow support.
Instead of a procedural language, we describe a declarative language based on con-
straints. The basic idea is that anything is allowed and possible unless explicitly
forbidden. To implement this idea we use a temporal logic: Linear Temporal Logic
(LTL). Although LTL has been around for decades, it has never been made acces-
sible for workflow design. Therefore, we provide a graphical notation and a set of
supporting tools. This nicely complements the core engine and design environment
of YAWL.
Before elaborating on our constraint-based approach, it is important to stress that
this is not a silver bullet. In reality, both flexibility and support are needed when it
comes to the computer-facilitated execution of processes and the various paradigms
offer different advantages. On the one hand, flexibility is needed for unpredictable
processes, where users can quickly react to exceptional situations and execute the
process in the most appropriate manner. On the other hand, support is needed when
it comes to processes that are repeatedly executed in the same manner, in situa-
tions that are too complex for humans to handle and where human mistakes must be
minimized. For example, the processing of insurance claims, customer orders, tax
declarations, etc. can benefit from a high degree of support because cases are repeat-
edly executed in a similar manner. Thus, an optimal balance between flexibility and
support is needed in order to be able to facilitate processes of various kinds. More-
over, in a large process there may be parts that require more flexibility and parts
that require more support. Therefore, procedural and flexible workflows should not
exclude each other. Instead, arbitrary decompositions of process models developed