Database Reference
In-Depth Information
FIGURE 7.2
Linked Geo Data browser. (© OpenStreetMap,
http://www.openstreetmap.org
,
contributors 2012, CC-BY-SA.
http://www.openstreetmap.org/copyright
)
A browser that displays RDF data against a slippy map, using OpenStreetMap
data, is available from the LinkedGeoData
59
project. The Linked Data from
OpenStreetMap is used to allow selection of certain geographical features (“facets”),
which are then marked on the map, as in Figure 7.2.
There are also several Semantic Search Engines that crawl and index Linked
Data to provide search facilities. These include the Semantic Web Search Engine
(SWSE)
60
(Hogan et al., 2011), which indexes OWL, RDF, and RSS data; Sindice
61
(a lookup index for the Semantic Web); and Swoogle
62
(which searches through
ontologies and instance data).
7.11 TESTING AND DEBUGGING LINKED DATA
Merea Maps has designed, created, and is ready to publish its Linked Data. Users
will be able access it through a Linked Data browser or an application that sends
SPARQL queries to Merea Maps' SPARQL endpoint. Merea Maps may also imple-
ment a Linked Data browser with mapping backdrop, similar to the GeoLinkedData
browser. However, the final stage before publication must be to pass quality assur-
ance—and indeed, testing should ideally be incorporated throughout, if not before,
the Linked Data creation process. There are a number of levels on which the Linked
Data must be checked for errors.
7.11.1 S
YntactIc
c
orrectneSS
The W3C RDF Validation Service
63
can check RDF/XML validity, and the tool
Eyeball
64
(which is part of the Jena framework) can identify specific syntax problems
like properties and classes that have not been declared in a schema, prefixes with no
namespace declared, ill-formed URIs, illegal datatypes, and untyped resources and
literals, among others.
