Databases Reference
In-Depth Information
Loosely related to the notion of meta-modelling in OWL, our A-Box also
contains the T-Box data (but not vice-versa). Thus, we can reason over schema
triples analogous to if they were assertions. We also split the body of rules into
a (possibly empty) A-Box and (possibly empty) T-Box graph pattern, where we
define a T-Box triple pattern as any pattern that can only unify with a T-Box
triple, and we define an A-Box triple pattern as the complement.
Example 8
Take the following OWL rule (
cax-eqc1
in OWL 2 RL/RDF):
(?
C
1
,
owl:equivalentClass
,
?
C
2
)
,
(?
X,
a
,
?
C
1
)
The first (underlined) triple pattern in the body is considered T-Box since
it can only be matched by T-Box triples. The second triple pattern in the
body is considered A-Box because it is not a T-Box pattern. We do not
need to categorise the head of the rule in this manner. Of course, the A-Box
pattern in the body may also match a T-Box triple, as per the previous
meta-modelling discussion.
(?
X,
a
,
?
C
2
)
←
♦
Authoritative reasoning then involves checking the source of T-Box knowl-
edge. Incorrect or malicious T-Box triples are the most “dangerous” in a rea-
soning context, where, for example, if a dataset contains millions of instances of
foaf:Person
, a single T-Box triple stated in an arbitrary location - such as one
of the following
foaf:Person rdfs:subClassOf ex:EvilEntity .
foaf:Person rdfs:subClassOf owl:Nothing .
can affect inferences computed for all the millions of instances of
foaf:Person
defined in Linked Data.
Authoritative Relation.
Next, we need to establish a relationship between RDF
sources and the set of RDF terms they speak authoritatively for. In the Linked
Data setting, we can establish this authoritative relation by directly using the
notion of dereferencing.
Definition 11 (Authoritative sources for terms).
We denote a mapping
from a source URI to the set of terms it speaks
authoritatively
for as follows:
2
C
auth
:
S
→
}∪
terms
(
get
(
s
))
B
s
→{
c
∈
U
|
redirs
(
c
)=
s
∩
A source is thus authoritative for all URIs that dereference to it and all blank
nodes it mentions. This formalises, for example, the intuitive relationship that
exists between the FOAF ontology and the set of terms in the
foaf:*
namespace
