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172 J. Lehmann et al. / DBpedia – A large-scale, multilingual knowledge base extracted from Wikipedia
| ontologyProperty = foaf:name }}
{{PropertyMapping
| templateProperty = manufacturer
| ontologyProperty = manufacturer }}
{{DateIntervalMapping
| templateProperty = production
| startDateOntologyProperty =
productionStartDate
| endDateOntologyProperty =
productionEndDate }}
{{IntermediateNodeMapping
| nodeClass = AutomobileEngine
| correspondingProperty = engine
| mappings =
{{PropertyMapping
| templateProperty = engine
| ontologyProperty = displacement
| unit = Volume }}
{{PropertyMapping
| templateProperty = engine
| ontologyProperty = powerOutput
| unit = Power }}
}}
(...)
}}
The RDF statements that are extracted from the pre-
vious infobox example are shown below. As we can
see, the production period is correctly split into a start
year and an end year and the engine is represented by
a distinct RDF node. It is worth mentioning that all
values are canonicalized to basic units. For example,
in the engine mapping we state that engine is a
Volume and thus, the extractor converts “4181cc” (cu-
bic centimeters) to cubic meters (“0.004181”). Addi-
tionally, there can exist multiple mappings on the same
property that search for different datatypes or different
units. For example, a number with “PS” as a suffix for
engine.
dbr:Ford_GT40
rdf:type dbo:Automobile;
rdfs:label "Ford GT40"@en;
dbo:manufacturer
dbr:Ford_Advanced_Vehicles;
dbo:productionStartYear
"1964"^^xsd:gYear;
dbo:productionEndYear "1969"^^xsd:gYear;
dbo:engine [
rdf:type AutomobileEngine;
dbo:displacement "0.004181";
]
(...) .
The DBpedia Mapping Wiki is not only used to map
different templates within a single language edition
of Wikipedia to the DBpedia ontology, but is used to
map templates from all Wikipedia language editions to
the shared DBpedia ontology. Figure 2 shows how the
infobox properties author and συγγαϕας – au-
thor in Greek – are both being mapped to the global
identifier dbo:author. That means, in turn, that in-
formation from all language versions of DBpedia can
be merged and DBpedias for smaller languages can
be augmented with knowledge from larger DBpedias
such as the English edition. Conversely, the larger
DBpedia editions can benefit from more specialized
knowledge from localized editions, such as data about
smaller towns which is often only present in the corre-
sponding language edition [43].
Besides hosting of the mappings and DBpedia on-
tology definition, the DBpedia Mappings Wiki offers
various tools which support users in their work:
– Mapping Syntax Validator The mapping syn-
tax validator checks for syntactic correctness and
highlights inconsistencies such as missing prop-
erty definitions.
– Extraction Tester The extraction tester linked on
each mapping page tests a mapping against a set
of example Wikipedia pages. This gives direct
feedback about whether a mapping works and
how the resulting data is structured.
– Mapping Tool The DBpedia Mapping Tool is a
graphical user interface that supports users to cre-
ate and edit mappings.
2.5. URI schemes
For every Wikipedia article, the framework intro-
duces a number of URIs to represent the concepts de-
scribed on a particular page. Up to 2011, DBpedia pub-
lished URIs only under the http://dbpedia.org domain.
The main namespaces were:
– http://dbpedia.org/resource/ (prefix dbr) for rep-
resenting article data. There is a one-to-one map-
ping between a Wikipedia page and a DBpedia
resource based on the article title. For example,
for the Wikipedia article on Berlin,
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DBpedia
will produce the URI dbr:Berlin. Exceptions in
this rule appear when intermediate nodes are ex-
tracted from the mapping-based infobox extrac-
tor as unique URIs (e.g., the engine mapping
example in Section 2.4).
– http://dbpedia.org/property/ (prefix dbp) for rep-
resenting properties extracted from the raw in-
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http://en.wikipedia.org/wiki/Berlin