WSML – a Language for WSMO - Enabling Semantic Web Services: The Web Service Modeling Ontology - page 83

Relations
Relations in WSML can have an arbitrary arity, they may be organized in a
hierarchy using subRelationOf , and the parameters may be typed using param-
eter type definitions of the form ( ofType type )and( impliesType type ), where
type is a concept identifier. The use of ofType and impliesType corresponds
to their use in attribute definitions. Specifically, parameter definitions with
the keyword ofType are used to check the type of parameter values, whereas
parameter definitions with the keyword impliesType are used to infer concept
membership of parameter values.
The allowed arity of a relation may be constrained by the underlying logic
of the WSML language variant. WSML-Core and WSML-DL allow only bi-
nary relations and, similar to attribute definitions, they allow only parameter
typing using the keyword impliesType .

Instances
A concept may have a number of instances associated with it. The instances
explicitly specified in an ontology are those which are shared as part of the
ontology. However, most instance data exist outside the ontology in private
databases. WSML does not prescribe how to connect such a database to an
ontology, since different organizations will use the same ontology to query
different databases and such corporate databases are typically not shared.
An instance may be a member of zero or more concepts and may have a
number of attribute values associated with it; see, for example, the instance
crimeAndPunishment in Listing 7.1. Note that the specification of concept mem-
bership is optional and that the attributes used in the instance specification
do not necessarily have to occur in the associated concept definition. Con-
sequently, WSML instances can be used to represent semistructured data,
since without concept membership and constraints on the use of attributes,
instances form a directed labeled graph. Because of this possibility to capture
semistructured data, most RDF graphs can be represented as WSML instance
data, and vice versa.

Axioms
Axioms provide a means to add arbitrary logical expressions to an ontology.
Such logical expressions can be used to refine concept or relation definitions
in the ontology, and also to add arbitrary axiomatic domain knowledge or to
express constraints. The axiom authorshipFromAuthor in Listing 7.1 states that
the relation authorship exists between any author and any book of which he/she
is an author; consequently, is in the relation

authorship . Logical expressions are explained in more detail in Section 7.2.3.

dostoyesksy , crimeAndPunishment

Web Servi ces

A Web service has a capability and a number of interfaces. The capability
describes the functionality of the Web service by expressing conditions on