Semantic Annotation for Process Models: - Department of Computer ...

3.1. PROCESS MODELING LANGUAGES 33
ment, data analysis, concurrent programming, reliability engineering and diagnosis of
programming. As a graphical modeling language, Petri nets can visualize dynamic behavior
with the nets consisting of place nodes (circles), transition nodes (bars) and arcs
connecting places with transitions. Places can contain tokens. Tokens are used in these
nets to simulate the dynamic and concurrent activities of systems. In a mathematical
form, the state of a Petri nets can be represented as a M vector, algebraic equations,
and other mathematical models governing the behavior of systems.
Due to such a small number of modeling constructs, Petri nets have the limited
expressivity of the structural, resources, organizational, functional or operational perspectives.
However, it performs very well on the data transaction and control perspectives.
Many execution, simulation and analysis techniques and applications have
been developed based on Petri nets. Numbers of extensions have also been made to deal
with the drawbacks of Petri nets, such as lacking data and hierarchy concepts, not useroriented
and scope limited to process aspects. The development of high-level Petri nets
and hierarchical Petri nets targets the data structuring and hierarchical decomposition
issues, e.g. coloured Petri nets [64]. User-oriented visualizations and complementary
modeling perspectives, e.g. for resources [30], structural [82] [83] [108], and time, have
been proposed.
3.1.2 EPC (Event-driven Process Chain)
EPC is a semi-formal graphical modeling language for business process workflows. It
was developed within the framework of ARIS [160] in the early 1990s. EPC has been
applied in ERP system describing workflow, e.g. SAP R/3, and now more widely.
Basic EPC notations only include events (hexagon), functions (rounded rectangle) and
connectors which can be transformed into Petri nets, but it introduces AND, OR and
XOR connectors. An example of the notations in an EPC model is illustrated in Figure
3.2. EPC emphases more on the operational/functional and control perspectives than
data transaction perspective as Petri nets do. An extended EPC includes organizational
units to represent roles or persons, information or resource object that can be seen as
input or output to functions, and process path to describe hierarchies of EPC processes.
A major strength of EPC is claimed to be its simplicity and easy-to-understand
notation. This makes EPC a widely acceptable technique to denote business processes.
Unfortunately, neither the syntax nor the semantics of EPC are well-defined [190]. EPC
requires non-local semantics [69], so that the meaning of any portion of the diagram
may depend on other portions arbitrarily far away. Recently, an XML-based EPC
— EPML (Event-driven Process Chain Markup Language) has been proposed by Jan
Mendling [105]. The motivation of EPML is to support data and model interchange
in the face of heterogeneous Business Process Modeling tools. Tool orientation deals
with the graphical representation of EPCs and EPML is able to store various layout
and position information for EPC elements [129].