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Chapter 6
Declarative Workflow

Maja Pesic, Helen Schonenberg, and Wil van der Aalst

6.1 Introduction

During the design of any information system, it is important to balance between flex-
ibility and support. This is of particular importance when designing process-aware
information systems. On the one hand, users want to have support from the system to
conduct their daily activities in a more efficient and effective manner. On the other
hand, the same users want to have flexibility, that is, the freedom to do whatever
they want and without being “bothered” by the system. Sometimes it is impossi-
ble to provide both flexibility and support because of conflicting requirements. The
continuous struggle between flexibility and support is illustrated by Fig. 6.1.
The right-hand-side of Fig. 6.1 shows the part of the spectrum covered by clas-
sical workflow management systems. These systems focus on processes that are
repeatedly executed in some predefined manner and are driven by procedural
languages. Note that in procedural workflow models there may be alternative paths
controlled by (X)OR-splits/joins. However, the basic idea is that the completion of
one task triggers other tasks. The YAWL nets described in earlier chapters provide
such a procedural language. Although the YAWL language is highly expressive, its
token-based semantics is most suitable for repetitive processes with tight control.
The left-hand-side of Fig. 6.1 shows the other end of the spectrum. Here pro-
cesses are less repetitive and the emphasis is on flexibility and user empowerment.
Here it is difficult to envision all possible paths and the process is driven by user
decisions rather than system decisions. Groupware systems (e.g., “enhanced” elec-
tronic mail, group conferencing systems, etc.) support such processes and focus on
supporting human collaboration and co-decision. Groupware systems do not offer
support when it comes to ordering and coordination of tasks. Instead, the high degree
of flexibility of these systems allows users to control the ordering and coordination
of tasks while executing the process (i.e., “on the fly”).
The trade-off between flexibility and support is an important issue in workflow
technology. Despite the many interesting theoretical results and the availability of

M. Pesic
Eindhoven University of Technology, Eindhoven, the Netherlands
e-mail: m.pesic@tue.nl

A.H.M. ter Hofstede et al. (eds.), Modern Business Process Automation, 175
DOI 10.1007/978-3-642-03121-2 6, c Springer-Verlag Berlin Heidelberg 2010