The Resource Description Framework - Linked Data: A Geographic Perspective - page 74

latitude is expressed as a floating point number, of unit degrees, and the Isis Tavern's
name is a string:
1 <?xml version = “1.0” encoding = “UTF-8”?>
2 <!DOCTYPE
3 <rdf:RDF [!ENTITY xsd http://www.w3.org/2001/XMLSchema# >]>
4 <rdf:RDF
5 xmlns:rdf = “ http://www.w3.org/1999/02/22-rdf-syntax-ns#”
6 xmlns:mereaMaps = “ http://mereamaps.gov.me/topo/” >
7 <rdf:Description
8 rdf:about = “ http://mereamaps.gov.me/topo/0012” >
9 <mereaMaps:has_name
10 rdf:datatype = “&xsd;string”/>The Isis Tavern
11 </mereaMaps:has_name>
12 <mereaMaps:has_latitude rdf:parseType = “Resource”>
13 <rdf:value
14 rdf:datatype = “&xsd;float”> 51.730031</rdf:value>
15 < http://mereamaps.gov.me/has_units
16 rdf:resource = “ http://mereamaps.gov.me/units/degrees”/ >
17 </mereaMaps:has_latitude>
18 </rdf:Description>
19 </rdf:RDF>
Lines 2 and 3 specify that the reference name xsd can be used in place of the
XML entity http://www.w3.org/2001/ # , which is just a way of abbreviating the
datatypes http://www.w3.org/2001/#string and http://www.w3.org/2001/#loat in
lines 10 and 14. Lines 9 to 11 state that the Isis Tavern has the name “The Isis
Tavern,” which is a string datatype. Lines 12 to 17 state, through the use of a
blank node that is not assigned a local identifier, that the Isis Tavern has a latitude
of 51.730031 that is a floating point datatype and has units (as specified by Merea
Maps' units namespace) of degrees.The last piece of RDF/XML syntax that we
discuss here concerns reification, . Reification is the process of making statements
about statements. This is particularly useful for adding provenance information
about the RDF triple, such as who wrote it and when. A word of warning though:
Reification causes problems when querying, so it is not recommended for use in
Linked Data. In Chapter 7, we discuss alternatives for including provenance infor-
mation without the use of reification. For now, though, it is worth being able to
recognize it. The following XML fragment gives an example of reification, showing
that the person codeMonkey1 at Merea Maps created the triple: mereaMaps:0012
mereaMaps:has _ name “The Isis Tavern.” A predicate dc:creator
is used, which comes from the Dublin Core vocabulary discussed in a further part
of this chapter.
1 <?xml version = “1.0” encoding = “UTF-8”?>
2 <rdf:RDF
3 xmlns:rdf = “ http://www.w3.org/1999/02/22-rdf-syntax-ns#”
4 xmlns:mereaMaps = “ http://mereamaps.gov.me/topo/”
5 xmlns:dc = “ http://purl.org/dc/elements/1.1/” >