S ISTEMAS R OTATIVOS D IRECCIONALES (R OTARY S TEERABLE S YSTEMS RSS)

A final feature of the Semantic Logger worth mentioning is the way the logger makes use of the FOAF model. A user’s FOAF file is used to allow a user to publish data about themselves, using a URI, allowing for the user’s data to be referred to from any dataset, or from within any context. The notion of using afoaf:PersonURI as a unique identifier for a person, has been highlighted in note on the ESW Wiki29, outlining the concept of a ‘person URI’ or a WebID. A WebID is presented as a unique web accessible resource used to describe a person. The Semantic Logger presents users with an ability to generate a simple FOAF file if they do not already have one at sign up see figure5.7.

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The Beagle Project: http://beagle-project.org

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NEPOMUK, the Social Semantic Desktophttp://nepomuk.semanticdesktop.org/

28_{KDE open-source desktop environment}

http://www.kde.org/

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Figure 5.7: Basic FOAF generating web interface built into the Semantic Logger

The concept of a web-based UI to aid the generation of a FOAF file has been taken one step further with foaf.qdos.com’s FOAF builder UI30.

Here it is important to stress the distinction between afoaf:Documentand afoaf:Person, which should have two separate URIs, as a foaf:Document is an information resource which is an RDF document on the web whereas afoaf:PersonURI is a non-information resource used to represent a person on the web. A common problem when minting new URIs for RDF data is that of selecting suitable URIs. The distinction between informa- tion and non-information resources are key when writing RDF. A URI for an information resource is one which can be sent across the wire, i.e. an RDF document, or an HTML document, whereas non-information resources represent things in the world which can not be sent across the wire, i.e. a URI for a person, or a URI for place. The author’s foaf:DocumentURI ishttp://mmt.me.uk/foaf.rdfis an information resource whose primary topic is a foaf:Person URI http://mmt.me.uk/foaf.rdf#mischa, the We- bID of the author. This notion of distinguishing the document (information resource) from the concepts presented within the document is best illustrated by Ren Magritte’s painting entitled “Ceci n’est pas une pipe” see figure 5.8.

The adoption of a WebID will empower users with the ability to uniquely identify them- selves on the web, allowing a given user the ability to associate public data on the web to themselves. Another advantage of the adoption of personal FOAF files is the ability for a user to define his/her friends, allowing for further connections to be made when using

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Figure 5.8: Ceci n’est pas une pipeRen Magritte - The Treachery of Images, 1928-1929

<http://mmt.me.uk/foaf.rdf> a foaf:Document .

<http://mmt.me.uk/foaf.rdf> foaf:primaryTopic <http://mmt.me.uk/foaf.rdf#mischa> . <http://mmt.me.uk/foaf.rdf#mischa> a foaf:Person .

<http://mmt.me.uk/foaf.rdf#mischa> foaf:homepage <http://mmt.me.uk/> .

Figure 5.9: Example FOAF triples

the system to identify communities of practise. This feature supports the incorporation of social annotations as described in Marc Davis’s work (Davis et al.,2006,2004). Both 3store (Harris and Gibbins,2003) and 4store (Harris et al.,2009) are quad-stores31, and not simply triple stores, all of the RDF triples held within the KBs are contextualised with respect to where the RDF data came from. For example, the below triples (see figure 5.9) present a URI for a foaf:Document, which has a primaryTopic which is a foaf:Person, who has a foaf:homepageof http://mmt.me.uk/.

The following quads (see figure 5.10) would be stored within a quad-store which in turn identifies the URI of the document where each of the above assertions originate from. The below notation is based on the non-standard n-quads notation as specified by Richard Cyganiak et al at http://sw.deri.org/2008/07/n-quads/. Whereby the fourth URI is the URI of the document where the triples originated from, this URI is known as a ‘model’ URI or the provenance URI. This allows the quad-stores, or knowledge bases, the ability to evaluate the legitimacy of the triples based on where the information came from. In the below example we can see that all of the Subject URIs of

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<http://mmt.me.uk/foaf.rdf> a foaf:Document <http://mmt.me.uk/foaf.rdf> . ...

<http://mmt.me.uk/foaf.rdf#mischa> a foaf:Person <http://mmt.me.uk/foaf.rdf> .

<http://mmt.me.uk/foaf.rdf#mischa> foaf:homepage <http://mmt.me.uk/> <http://mmt.me.uk/foaf.rdf> .

Figure 5.10: Example FOAF quads

Count Entity Type

http://xmlns.com/foaf/0.1/Person 19, 007, 420 http://xmlns.com/foaf/0.1/Document 4, 918, 936 http://purl.org/goodrelations/v1#ProductOrServiceModel 1, 408, 940 http://purl.org/goodrelations/v1#UnitPriceSpecification 784, 786 http://blogs.yandex.ru/schema/foaf/Posts 585, 188 http://purl.org/goodrelations/v1#BusinessEntity 540, 861 http://purl.org/goodrelations/v1#Offering 439, 130 http://www.w3.org/2002/07/owl#Ontology 436, 809 http://purl.org/goodrelations/v1#TypeAndQuantityNode 421, 255 http://purl.org/goodrelations/v1#ProductOrServicesSomeInstancesPlaceholder 363, 863 Table 5.1: Top Ten most prevalent RDF types as perhttp://pingthesemanticweb.

com/on 14/07/2009

the triples are either the same as the model URI or a fragment of the model URI, and as a result we can safely trust all of the statements made.

Table 5.1 presents statistics taken from the “Ping the Semantic Web” service which maintains a list of URLs for RDF resources found of the web. This tables is used to illustrate how much FOAF data exists on the web, and a big part of the Semantic Web is made up of data pertaining to people. Up-to-date statistics can be found at the following URLhttp://pingthesemanticweb.com/stats/types.php.