D2R Server – Publishing Relational Databases on the Semantic Web
Christian Bizer and Richard Cyganiak
Freie Universität Berlin
D2R Server is a tool for publishing the con-
tent of relational databases on the Semantic Web.
Database content is mapped to RDF by a declar-
ative mapping which specifies how resources are
identified and how property values are generated
from database content. Based on this mapping,
D2R Server allows Web agents to retrieve RDF and
XHTML representations of resources and to query
non-RDF databases using the SPARQL query lan-
guage over the SPARQL protocol.
ated representations are richly interlinked on RDF
and XHTML level in order to enable browsers and
crawlers to navigate database content.
The W3C recommendation Architecture of the World Wide
Web, Volume One [Jacobs and Walsh, 2004] specifies the prin-
ciples of the Web: Items of interest are called resources and
are identified by URIs. Web agents may retrieve representa-
tions of resources by dereferencing URIs. The data format of
a representation is determined by content negotiation relying
on Internet media types. The main access paradigms to the
Web are hyperlink navigation and search.
In this demonstration, we present an approach to publish-
ing the content of relational databases on the Web which fo-
cuses on compliance with these principles. We introduce
D2R Server, a system for publishing relational data on the
Web. D2R Server enables RDF and HTML browsers to nav-
igate the content of non-RDF databases, and allows appli-
cations to query a database using the SPARQL query lan-
guage over the SPARQL protocol. The server takes requests
from the Web and rewrites them to SQL queries. This on-
the-fly translation allows the content of large databases to be
accessed with acceptable response times. In the following,
we describe how D2R Server handles the mapping from re-
lational data to RDF, URI allocation, URI dereferencing, hy-
perlinking and search.
2 Mapping Rel