Information Technology Reference
In-Depth Information
6.2.1 Capability
The functionality offered by a given service is described by its capability. This
is expressed by the state of the world before the service is executed and the
state of the world after successful service provision. The capability of a service
can be used for discovery and selection purposes, i.e. the capability is used by
the requester to determine whether the service meets its needs.
Specified more formally in MOF, a capability is made up of the following
elements:
Class
capability
hasNonFunctionalProperty
type
nonFunctionalProperty
importsOntology
type
ontology
usesMediator
type
ooMediator
hasPrecondition
type
axiom
hasAssumption
type
axiom
hasPostcondition
type
axiom
hasEffect
type
axiom
The set of nonfunctional properties that can be attached to a capability is
presented in Section 6.5. The attributes of
imported ontologies
and
mediators
play the same role for ontologies.
•
Preconditions.
Preconditions in the description of a capability specify the
required state of the information space before the execution of the service,
i.e. they specify what information a Web service expects in order to provide
the service. Preconditions constrain the set of states of the information
space such that any state satisfying these constraints can serve as a valid
starting state (in the information space) for executing the service in a
defined manner.
•
Assumptions.
Assumptions in the description of a capability describe the
state of the world which is assumed before the execution of the service.
Otherwise, the successful provision of the service is not guaranteed. As
opposed to preconditions, assumptions are not necessarily checked by the
service. We make this distinction in order to allow the explicit idea of
conditions on the state of the world that are outside the information space.
•
Postconditions.
Postconditions in the description of a capability describe
the state of the information space that is guaranteed to be reached after the
successful execution of the service; they also describe the relation between
the information that is provided to the service and its results.
•
Effects.
Effects in the description of a capability describe the state of the
world that is guaranteed to be reached after the the successful execution
of the service, i.e. if the preconditions and the assumptions of the service
are satisfied.
6.2.2 Interfaces
An interface describes how the functionality of a service can be achieved (i.e.
how the capability of a service can be fulfilled) by providing a twofold view
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