Databases Reference
In-Depth Information
SELECT ?comp ?name WHERE {
dbr:SAP_AG foaf:name ?name .
?comp skos:prefLabel ?name .
}
Answers (other than
dbr:SAP AG
)cannotbereachedfromthestartingURI
dbr:SAP AG
because the relevant documents are connected together by the
literal
"SAP AG"
, which cannot be traversed as a HTTP link.
♦
Example 15
Dereferencing partial information:
In the general case, the effectiveness
of LTBQE is heavily dependent on the amount of data returned by the
deref
(
u
) function. In an ideal case, dereferencing a URI
u
would return all
triples mentioning
u
on the Web of Data. However, this is not always the
case; for example:
SELECT ?s WHERE {
?s owl:sameAs dbr:SAP_AG .
}
This quite simple query cannot be answered by link-traversal techniques
since the triple “
nyt:75293219995342479362 owl:sameAs dbr:SAP AG .
”
is not accessible by dereferencing
dbr:SAP AG
or
owl:sameAs
.
♦
The assumption that all RDF available on the Web of Data about a URI
u
can be collected by dereferencing
u
is clearly idealised; hence, later in Section 6.4
we will empirically analyse how much the assumption holds in practice, giving
insights into the potential recall of LTBQE on an infrastructural level.
6.3 LiDaQ: Extending LTBQE with Reasoning
Partly addressing some of the shortcomings of the LTBQE approach in terms of
completeness (or, perhaps more fittingly,
recall
), Hartig
et al.
[33] proposed an
extension of the set of query relevant sources to consider
rdfs:seeAlso
links,
which sometimes overcomes the issue of URIs not being dereferenceable (as per
nytimes:nytd org
in our example).
On top of this extension, we previously proposed a system called “LiDaQ”
that extends the baseline LTBQE approach with components that leverage
lightweight RDFS and
owl:sameAs
reasoning in order to improve recall. Formal
