Information Technology Reference
In-Depth Information
provides
Resource
Service
supports
presents
describedBy
ServiceProfile
ServiceGrounding
ServiceModel
What the service does...
How to access it...
How itworks...
Fig. 8.1.
OWL-S conceptual model
ing and serves as a template for service requests, thus enabling discovery and
matchmaking. The profile comprises nonfunctional aspects such as references
to existing categorization schemes (e.g. UNSPC) or ontologies, provider infor-
mation, and the quality rating of the service. The most essential information
presented in the profile, however, is the specification of what functionality
the service provides. Information transformation is represented by
inputs
and
outputs
; the change in the state of the real world caused by the execution
of the service is represented by
preconditions
and
effects
. Inputs and outputs
refer to OWL classes describing the types of instances to be sent to the service
and the respective responses to be expected. The format of the preconditions
and effects is not fixed, but the authors of OWL-S allow various formats to
be embedded into the OWL ontology. Preferably, SWRL [64]; alternatively,
DRS [88] or KIF [46] expressions may be allowed.
A possible problem in this context is that the semantics of these conditions
is not covered by the (description logics) expressivity of the OWL-S ontology
itself, but by reference to these languages. Parties, exchanging OWL-S profile
descriptions or using OWL-S for discovery, need to agree on the language for
expressing conditions and the notions of a “match” which is not addressed in
the standard as such.
8.1.2 Service Model
A service might be
described by
a service model which exposes “how a service
works”. The main use of a service model is to enable invocation, enactment,
composition, monitoring, and recovery. The service model views the interac-
tions of the service as a process. A process is not necessarily a program to
be executed, but rather a specification of ways in which a client may inter-
act with a service. OWL-S distinguishes between atomic processes, simple
processes, and composite processes. Atomic processes are simple operations,
whereas simple processes are views of complex or atomic processes. Composite
processes are built up from atomic or simple processes by standard workflow
constructs such as sequence, split, or join to determine the control flow, plus
additional dataflow information (which outputs are routed to which inputs
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