Information Technology Reference
In-Depth Information
Particularities of the WSML Variants
Each of the WSML variants defines a number of restrictions on the logical-
expression syntax. For example, logic programming rules and constraints are
not allowed in WSML-Core and WSML-DL. Table 7.1 presents a number of
language features and indicates in which variant each feature can occur:
Table 7.1.
WSML variants and feature matrix
Feature
Core DL Flight Rule Full
Classical negation (
neg
)
-X - -X
Existential quantification
-
X
-
-
X
(Head) disjunction
-
X
-
-
X
n
-ary relations
-
-
X
X
X
Metamodeling
-
-
X
X
X
Default negation (
naf
)
-
-
XXX
LP implication
-
-
X
X
X
Integrity constraints
-
-
X
X
X
Function symbols
-
-
-
X
X
Unsafe rules
-
-
-
X
X
•
WSML-Core
allows only first-order formulas which can be translated to
the description logic programming (DLP) subset of
(
D
) [50]. This
subset is very close to the 2-variable fragment of first-order logic, restricted
to Horn logic. Although WSML-Core might appear in Table 7.1 as fea-
tureless, it captures most of the conceptual model of WSML, but has only
limited expressiveness within the logical expressions.
SHIQ
•
WSML-DL
allows all first-order formulas which can be translated to
SHIQ
(
D
). This subset is very close to the two-variable fragment of first-
order logic. Thus, WSML DL allows classical negation, and disjunction
and existential quantification in the heads of implications.
•
WSML-Flight
extends the set of formulas allowed in WSML-Core by al-
lowing variables in place of instance, concept, and attribute identifiers and
by allowing relations of arbitrary arity. In fact, any such formula is allowed
in the head of a WSML-Flight rule. The body of a WSML-Flight rule al-
lows conjunction, disjunction and default negation. The head and body
are separated by the LP implication symbol. WSML-Flight additionally
allows metamodeling (e.g. using a class identifier simultaneously as an in-
stance) and reasoning over a signature, because variables are allowed to
occur in place of concept and attribute names.
•
WSML-Rule
extends WSML-Flight by allowing function symbols and un-
safe rules, i.e. variables which occur in the head or in a negative body
literal do not need to occur in a positive body literal.
Search WWH ::
Custom Search