The Resource Description Framework - Linked Data: A Geographic Perspective - page 83

For our purposes in GI, SKOS is of most interest when we want to indicate some
relationship between vocabularies or ontologies where we do not have enough infor-
mation to specify exact links or where the vocabularies themselves have come from
imprecise data, such as crowd-sourced tags.
FOAF , the Friend of a Friend project (Brickley and Miller, 2010), defines an RDF
vocabulary for expressing metadata about people and their interests, relationships,
and activities. The main class that is used is foaf:Person , which can take prop-
erties like foaf:name , foaf:gender , foaf:member , foaf:organization ,
and foaf:mbox , the last indicating the person's e-mail address. We might reuse
foaf:name in our Topo ontology instead of defining our own “ has _ name ”
property, for example. 12 FOAF does not assign a URI to a person, however, because
there is still a debate about assigning one URI to a person. Who should mint it?
What happens when a person has multiple URIs? To get around this problem, FOAF
places a restriction on certain properties 13 so that when a property is used in a triple,
the property's object value uniquely defines the subject resource. One example of this
is foaf:mbox (the property “has email address”), implying that an e-mail address
can be said to pinpoint one specific person. If one person called Bob has an e-mail
address [e-mail] , and another person called Robert has an e-mail address
[e-mail] , then we can infer that Bob and Robert are the same person. This
is also an example of where FOAF may not have gotten things right as there are
many occasions when people share e-mail addresses; therefore, the inference would
be incorrect.
The other frequently used property that FOAF provides is foaf:knows , which
specifies that person A knows person B (although it may be unrequited; person B may
deny all knowledge of person A in return). This can then be used to build a graph of
the social networks between people, which can be useful in many applications.
5.7.1 g eo RDF
The W3C's Basic Geo WGS84 lat/long vocabulary 14 is widely used on the Linked Data
Web to represent very basic spatial location information, using WGS84 as a reference.
It only includes the classes geo:SpatialThing and geo:Point . A geo:Point
can have the relationships geo:lat (for latitude), geo:long (for longitude), and
geo:alt (for altitude). Our Pub example could hence be rerendered using the “ geo ”
and “ foaf ” namespaces as
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:geo = “ http://www.w3.org/2003/01/geo/wgs84_pos#”
5 xmlns:foaf = “ http://xmlns.com/foaf/0.1/” >
6 <rdf:Description
7 rdf:about = “ http://mereamaps.gov.me/topo/0012” >
8 <rdf:type rdf:resource = “ http://mereamaps.gov.me/topo/Pub”/ >
9 <foaf:name>The Isis Tavern</foaf:name>
10 <geo:long>-1.241712</geo:long>