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

4.4. META-MODEL ANNOTATION 71
4.4.1 GPO (General Process Ontology)
For meta-model annotation, a process ontology is an explicit and formal specification
of concepts which are used to model processes in general. It is supposed to provide
common and core semantics of process modeling constructs. We have investigated a
number of process modeling languages and process ontologies in Chapter 3. Most of
them were not initiated for annotation purposes and are not represented in OWL,
except OWL-S. OWL-S is designed to describe processes of Web services in OWL.
Although a process model in our approach may be regarded as a service, the difference
between a Web service and a process model is that a Web service is executable and uses
programming-like control constructs as their basic building blocks which are inadequate
for all the modeling issues, especially for the type level of modeling. Therefore, we
propose a new ontology for meta-model annotation purpose in our framework.
It is difficult to build an ontology to cover all the semantics of various modeling
constructs, which would be very complicated. To facilitate the annotation, representations
of the ontology should be easily understandable and able to preserve enough
semantics of process knowledge. As Musen stated [109]: "Although no simple predicate
tells us unambiguously whether a particular specification is an ontology, we can still
agree on certain things. We can agree that ontologies enumerate the salient concepts
in an application area." A process ontology therefore consists of core concepts which
can present the process perspectives specified in Chapter 3.
We set a design principle of the process ontology as simple but comprehensive for
modeling process knowledge. Based on such principle, we create an ontology for process
modeling, namely General Process Ontology (GPO).
Main concepts defined in GPO
The main concepts in GPO are Activity, Artifact, Actor-role, Input, Output,
Precondition, Postcondition, Exception and WorkflowPattern. GPO consisting
of those concepts and their relationships are represented using RML [168] in Figure 4.5.
• Activity is a central concept which composes a process. Activity is a synonym of
process. However, we also found Process is seldom a construct or just a package
construct in most process modeling languages because it is obvious that a process
model describes processes. Event is used to trigger Activities but it is sometimes
used like an Activity. It also sometimes mixed with state. In order to avoid
any ambiguity of those concepts, event and state are not included in GPO. We
still think event and state are crucial for process models at the execution level
but less at the conceptual business process level. We therefore use the concept
Activity in our general process ontology. An activity may be an atomic activity or
a composed activity represented by the aggregation relation between activities,
i.e. one activity is a subActivity of another activity.
• Artifact represents something involved in an activity such as product, information,
tool and software.
• Input and Output of an Activity specify what are consumed and produced by
this activity respectively. The way an Artifact is involved in an activity can be