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Chapter 12
The Declare Service

Maja Pesic, Helen Schonenberg, and Wil van der Aalst

12.1 Introduction

The Declare Service is a YAWL Custom Service that enables decomposing YAWL
tasks into DECLARE workflows, that is, workflows supported by the workflow man-
agement system (WfMS) called DECLARE. The goal of this service is to enable
a particular kind of flexibility. Chapter 6 describes a constraint-based approach
to workflow models and the ConDec language. This approach, supported by the
DECLARE WfMS, allows for more flexibility, that is, execution of tasks is allowed
if it is not explicitly forbidden by some constraint. This chapter describes DECLARE
and the Declare Service for YAWL.
Sometimes it is easier to express a process in a procedural language (e.g., the
native workflow language of YAWL) and sometimes a declarative approach is more
suitable. Moreover, in a larger process it may be useful to express parts of the pro-
cess in a procedural language and specify other parts in terms of constraints. Using
the service-oriented architecture of YAWL, this can easily be realized. A YAWL task
may decompose into a DECLARE process and a task in DECLARE can be decom-
posed into a YAWL process. Arbitrary decompositions of DECLARE and YAWL
models allow for the integration of declarative and YAWL workflows on different
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abstraction levels. This way the designer is not forced to make a binary choice
between a declarative and a procedural way of modeling. Hence, a seamless inte-
gration can be achieved, where parts of the workflow that need a high degree of
flexibility are supported by declarative DECLARE models, and parts of the processes
that need centralized control of the system are supported by YAWL models.
Consider, for example, the decomposition of the Carrier Appointment process
shown in Fig. 12.1. At the highest level of decomposition, the main process is
modeled using a procedural YAWL Carrier Appointment net, which is described

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Note that the service oriented architecture also allows for decompositions involving worklets,
which are described in Chaps. 4 and 11.
M. Pesic (B )
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, 327
DOI 10.1007/978-3-642-03121-2 12, c Springer-Verlag Berlin Heidelberg 2010