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1 Introduction 17
Workflows may need to evolve over time, have to deal with unforeseen excep-
tions, and sometimes their specification is more easily achieved by specifying
constraints that need to be satisfied at runtime rather than by providing an explicit
road map for all possible execution paths. In Part III, various aspects of flexibility
are examined.
Part IV discusses the core YAWL environment, its architecture, its design com-
ponent, and its main runtime component. YAWL’s architecture is service-oriented,
which means that its various components communicate through well-defined inter-
faces. The design component allows the creation and verification of workflows.
Once completed, they can be passed to the runtime component, the Engine, for
execution.
In Part V, a number of services are presented, which can interact with the core
YAWL environment and provide additional functionality. The services discussed
provide concrete ways of achieving flexibility in workflow specification and execu-
tion (the Worklet Service and the Declare Service) or deal with work distribution,
allowing the Engine to remain resource-agnostic (the Resource Service).
Part VI positions YAWL with respect to a number of well-known approaches
to business process specification and/or execution, the Business Process Modeling
Notation (BPMN), Event-driven Process Chains (EPCs), the Business Process Exe-
cution Language (BPEL), and a number of other well-known open-source workflow
management systems. It is shown how BPMN models can be mapped to YAWL nets,
how EPCs compare to YAWL and how they can be mapped to YAWL nets and vice
versa, how BPEL relates to YAWL, and how open-source workflow management
systems such as jBPM and OpenWFE compare with YAWL.
In Part VII a number of advanced topics in the field of BPM are examined. The
connection with the Process Mining (ProM) framework is discussed and it is demon-
strated how this framework can be used to mine valuable information from execution
logs that have been generated by the YAWL environment. Correctness notions for
YAWL specifications are introduced and precisely defined and it is shown how,
and to what extent, these notions can be automatically verified. Sometimes new
process models can be derived from existing process models and the notion of pro-
cess configuration is explored in more depth through the C-YAWL (Configurable
YAWL) approach. Finally, workflows may be running in different settings (e.g. dif-
ferent organizations or departments), but there may be a need for them to exchange
information. Ideally such needs are expressed at the specification level, not at the
implementation level.
Part VIII discusses two applications in which the YAWL environment has been
used. One of these applications is in the healthcare domain, and the other is in the
domain of film production.
Part IX concludes the book and provides an outlook for future developments.