Database Reference
In-Depth Information
7 Publishing Linked Data
7.1 INTRODUCTION
In Chapter 5, we introduced the Resource Description Framework (RDF), the World
Wide Web Consortium (W3C) standard markup language for encoding Linked Data,
and in Chapter 6, we demonstrated how Geographic Information (GI) could be mod-
eled in RDF. In this chapter, we explain how to take the GI you have, which may be
in a relational database (RDB), GIS (Geographic Information Systems), or stored as
XML (eXtensible Markup Language) files based on Geography Markup Language
(GML), and convert it to RDF for publication as Linked Data. The purpose of publish-
ing your GI as Linked Data is so that it can be more easily reused. This chapter first
states the main principles of Linked Data, as originally set out by Tim Berners-Lee
(2006), then discusses how to design an RDF data model based on the structure
of your current GI. We also look at the tools available for storing, publishing, and
querying your RDF data, as well as introduce methods for including metadata about
where the data has come from (its provenance) and its licensing terms.
Consideration must also be given to linking your dataset to others on the Web of
Data, so that it can be easily discovered. Hence, in Chapter 8 we explain the mecha-
nisms for selecting the most appropriate links between your data and others', which
in effect is addressing the problem of data integration.
7.2 LINKED DATA PRINCIPLES
The four Linked Data Principles as set out by Berners-Lee in his Linked Data Design
Note (Berners-Lee, 2006) are as follows:
1. Use Uniform Resource Identifiers (URIs) as names for things.
2. Use Hypertext Transfer Protocol (HTTP) URIs so that people can look up
those names.
3. When someone looks up a URI, provide useful information, using the stan-
dards (RDF, SPARQL).
4. Include links to other URIs so that they can discover more things.
The first point is self-explanatory; we have already covered the use of URIs to
name things in the real world, and that we need to assign URIs for the things them-
selves separate from the URIs assigned to the Web resources describing those things.
The second point is again a technique that we are already using: Merea Map's URIs
are of the form http://id.mereamaps.gov.me/something . But, it is worth explaining
why Tim Berners-Lee thought it was so important to have URIs based on HTTP.
HTTP URIs mean that the URI can be looked up on the Web, and we can retrieve the
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