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ClassMap) through foaf:homepage property. The mapping is performed if and only if
the specified condition (see d2rq:condition ) is verified.
It is worth noticing that the generated URIs are formed by a prefix, in our
case , the name of the concept, and an
At the end of this phase, the Linked Open IPA data set was produced, as
depicted in Figure 12.2. The following RDF triples are generated by the clause in
Figure 12.3 over the above IPA data example.
12.4.4 External Linking and Self-Description Metadata
However, to further enrich the data set (fulfilling the fourth LOD principle), and
to better integrate it into the LOD cloud context, we searched for existing public
data that represent similar concepts to ours. We found that the IPA contains geo-
graphical data (e.g., municipalities and regions) that are also present in well-known
data sets of the LOD cloud such as DBpedia (Auer et al., 2007) and Geonames
(Geonames ontology, 2012). Therefore, we created external interlinks between
them and Linked Open IPA, thus connecting IPA to the LOD cloud (see Figure
12.2). The interlinks are represented by the logic equivalence of two RDF resources
and can be expressed and materialized using the OWL property sameAs.
In particular, this phase was driven by string similarity between the municipali-
ties' URIs in Linked Open IPA and those in DBpedia. Thus, we firstly imported
DBpedia's URIs of municipalities into our relational DBMS (specifically in the table
column “ geodata.dbpedia ”), and then we executed another D2RQ script.
The script allows us to produce the RDF triples of the interlinks with DBpedia, and
it is illustrated in Figure 12.4.
In practice, the clause in Figure 12.4 connects IPA municipalities' entities to
corresponding DBpedia municipalities through the property ( owl:sameAs ). he
connection is valid if the specified SQL condition (see d2rq:condition ) is sat-
isfied to the municipalities.
The direct linking toward Geonames was made exploiting the already existing
links between DBpedia and Geonames, that is, using the transitive property of the
Figure 12.4
D2RQ script for producing interlinks with DBpedia.
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