Databases Reference
In-Depth Information
the erroneous or inaccurate annotations, classifications or representations. An RDF val-
idator can be used to parse the RDF document and ensure that it is syntactically valid,
that is, to check whether the document is in accordance with the RDF specification.
Example.
Let us assume that the user is looking for flights between two specific lo-
cations, for instance Paris (France) and New York (United States) using the example
flight search engine. However, the user is returned with no results. A possible reason
for this is that one of the data sources incorrectly uses the property geo:lon to specify
the longitude of "Paris" instead of using geo:long. This causes a query to retrieve no
data when querying for flights starting near to a particular location.
Definition 19 (Interlinking).
Interlinking refers to the degree to which entities that
represent the same concept are linked to each other.
Metrics.
Interlinking can be measured by using network measures that calculate the in-
terlinking degree, cluster coe
cient, sameAs chains, centrality and description richness
through sameAs links.
Example.
In the example flight search engine, the instance of the country "United
States" in the airline dataset should be interlinked with the instance "America" in the
spatial dataset. This interlinking can help when a user queries for a flight as the search
engine can display the correct route from the start destination to the end destination
by correctly combining information for the same country from both the datasets. Since
names of various entities can have di
ff
erent URIs in di
ff
erent datasets, their interlinking
can help in disambiguation.
Definition 20 (Consistency).
Consistency means that a knowledge base is free of (log-
ical
formal) contradictions with respect to particular knowledge representation and in-
ference mechanisms.
/
Metrics.
On the Linked Data Web, semantic knowledge representation techniques are
employed, which come with certain inference and reasoning strategies for revealing im-
plicit knowledge, which then might render a contradiction. Consistency is relative to a
particular logic (set of inference rules) for identifying contradictions. A consequence
of our definition of consistency is that a dataset can be consistent wrt. the RDF infer-
ence rules, but inconsistent when taking the OWL2-QL reasoning profile into account.
For assessing consistency, we can employ an inference engine or a reasoner, which sup-
ports the respective expressivity of the underlying knowledge representation formalism.
Additionally, we can detect functional dependency violations such as domain
range vi-
olations. In practice, RDF-Schema inference and reasoning with regard to the di
/
erent
OWL profiles can be used to measure consistency in a dataset. For domain specific ap-
plications, consistency rules can be defined, for example, according to the SWRL [64]
or RIF standards [73] and processed using a rule engine.
Example.
Let us assume a user is looking for flights between Paris and New York on
the 21st of December, 2012. Her query returns the following results:
ff
Flight
From
To
Arrival
Departure
A123
Paris
NewYork
14:50
22:35
A123
Paris
Singapore
14:50
22:35
