WSML – a Language for WSMO - Enabling Semantic Web Services: The Web Service Modeling Ontology - page 86

in which the variable occurs is the scope of quantification), unless indicated
otherwise, through the sharedVariables construct (see Section 7.2.2).
Terms are either identifiers, variables, or constructed terms. An atom is,
as usual, a predicate symbol with a number of terms as arguments. Besides
the usual atoms, WSML has special kinds of atoms, called molecules ,which
are used to capture information about concepts, instances, attributes and
attribute values. There are two types of molecules, analogous to the situation
in F-Logic:

• An isa molecule is a concept membership molecule of the form A memberOf

B or a subconcept molecule of the form A subConceptOf B ,where A and B
are arbitrary terms.

• An object molecule is an attribute value expression of the form

A [ B hasValue C ] , a constraining-attribute signature expression of the form
A [ B ofType C ] , or an inferring-attribute signature expression of the form
A [ B ofType C ] ,where A,B, and C are arbitrary terms.

WSML has the usual first-order connectives: the unary negation operator
neg , and the binary operators for conjunction and , disjunction or , right im-
plication implies , left implication impliedBy , and dual implication equivalent .
Variables may be universally quantified using forall or existentially quantified
using exists . First-order formulas are obtained by combining atoms using the
above connectives in the usual way. The following are examples of first-order
formulas in WSML:
//Every person has a father
forall ?x (?x memberOf Person implies exists ?y (?x[ father hasValue ?y])) .
//John is member of a class which has some attribute called 'name'
exists ?x,?y (john memberOf ?x and ?x[name ofType ?y]).

In addition to first-order formulas, WSML allows the use of the negation-
as-failure symbol naf on atoms, the special logic programming implication
symbol :- , and the integrity constraint symbol !- . A Logic Programming rule
consists of a head and a body , separated by the symbol :- . An integrity con-
straint consists of the symbol !- followed by a rule body. Negation-as-failure
naf is allowed to occur only in the body of a logic programming rule or an
integrity constraint. The further use of logical connectives in Logic Program-
ming rules is restricted. The following logical connectives are allowed in the
head of a rule: and , implies , impliedBy ,and equivalent . The following connec-
tives are allowed in the body of a rule (or constraint): and , or ,and naf .The
following are examples of logic programming rules and database constraints:
//Every person has a father
?x[ father hasValue f(?y)] : − ?x memberOf Person.
//Man and Woman are disjoint
! − ?x memberOf Man and ?x memberOf Woman.
//In case a person is not involved in a marriage, the person is a bachelor
?x memberOf Bachelor : − ?x memberOf Person and naf Marriage(?x,?y,?z).