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specifies the desired mediation facility which is then detected by a discov-
ery mechanism; or via another mediator when a mediation service is to be
used that is not interoperable with the first mediator.
6.4.2 WSMO Mediator Types
In order to allow the resolving of heterogeneities between different WSMO
components, WSMO defines several different types of mediators for connect-
ing different WSMO components and overcoming the heterogeneities that can
arise between those components: OO mediators, GG mediators, WG media-
tors, and WW mediators. All mediators are subclasses of the general WSMO
mediator class defined above, where the prefix indicates the components con-
nected by the particular type of mediator. The following explains the various
WSMO mediator types.
OO Mediators
OO mediators resolve mismatches between ontologies and provide mediated
domain knowledge specifications to the target component. The source compo-
nents are ontologies or other OO mediators that are heterogeneous and able
to be integrated, and the target component is any WSMO top-level concept
that applies to the integrated ontologies. The following shows the description
specialization of an OO meditator:
Class
ooMediator
sub
−
Class
mediator
hasSource
type
{
ontology, ooMediator
}
OO mediators are used to import the terminology required for a resource
description whenever there is a mismatch between the ontologies to be used.
The mediation technique used by OO mediators is mainly ontology integra-
tion, i.e. merging, aligning, and mapping ontology definitions in order to re-
trieve integrated, homogeneous terminology definitions.
GG Mediators
A GG mediator connects goals, allowing one to create a new goal from existing
goals and thus defining goal ontologies. GG mediators are defined as follows:
Class
ggMediator
sub
−
Class
mediator
usesMediator
type
ooMediator
hasSource
type
{
goal, ggMediator
}
hasTarget
type
{
goal, ggMediator
}
A GG mediator might use an OO mediator to resolve terminology mis-
matches between the source goals. Mediation services for GG mediators reduce
or combine the descriptions of the source goals into the newly created target
goal.
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