Wednesday, November 4, 2015

Some important RDF(S) Vocabularies

In the last lab course, we've used the Dublin Core vocabulary to represent bibliographic information as well as the FOAF vocabulary to describe persons and their relationships. In general, a vocabulary usually defines a set of terms to be used. Likewise in the Semantic Web or the Web of Data, there exist a number of well established vocabularies - all based on RDF(S) or RDF(S) and OWL - that are (re-)used for the publication of (semantic) data. Here, data publishers consequently combine terms from existing vocabularies with proprietary ones covering their very specific needs. In the following, you will find some popular vocabularies that will also be used in the lecture:

Dublin Core Metadata Initiative provides a set of metadata for describing numerical and physical resources, esp. for bibliographic purposes. Widespread properties in the Web of Data include:

  • dcterms:creator to specify the maker of a resource,
  • dcterms:date to specify a date related to the resource, or
  • dcterms:description to add a description of a resource, or
  • dcterms:subject to specify the topic of a resource.

Friend-of-a-Friend project (FOAF) proposes a widespread vocabulary for the description of persons, their social links and relations to other objects. Several social networks are using FOAF vocabulary to expose their data:

FOAF data establishes a distributed social network.

Semantically-Interlinked Online Communities (SIOC) is another very important vocabulary to describe social networks. SIOC exporters exist for WordpressDrupal or vBulletin. Prominent properties in the SIOC vocabulary are, as e.g., :

  • sioc:hasCreator describes the creator of an object
  • sioc:content text-only representation of content (as e.g. a blog post)
  • sioc:topic indicating the topic of a resource.

Simple Knowledge Organisation System (SKOS) is used to describe concept hierarchies such as taxonomies, folksonomies, or thesauri. SKOS provides properties to represent subsumption hierarchies:

  • skos:narrower describes a more specific concept,
  • skos:broader describes a more general concept.

SKOS vocabulary is a powerful tool to describe domain ontologies, where the rdfs:subClassOf would be insufficient or not suited to describe a hierarchical relationship. Just take into account the following example:

Albert Dubois-Pillet: The Banks on the Marne at Dawn (c. 1888)
A pointilistic painting, which is also an impressionistic painting.
But not all pointilistic paintings are also impressionistic paintings.

Thus, Pointilistic Painters in general are not a valid subclass of Impressionistic Painters, simply because there are some pointilistic painters that are not counted as impressionistic painters, but started a new art style like Henri-Edmond Cross, who developed from Pointilism to Neo-Impressionism and went on to Fauvism. Nevertheless, the concept 'Impressionistic Painters' is a more general concept than the concept 'Pointilistic Painters', because Pointilism branched from the Impressionistic movement.

Thus we might say:

  • ex:ImpressionisticPainters skos:narrower ex:PointilisticPainters .
    ex:PointilisticPainters skos:broader ex:ImpressionisticPainters .

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