SPCData: The Italian Public Administration Data Cloud - Information and Communication Technologies in Public Administration - page 258

User interface and applications

Trust

Proof

Unifying logic

Ontologies:
OWL

Rules:
RIF/SWRL

Querying:
SPARQL

Ta xonomies: RDFS

Data interchange: RDF

Syntax: XML

Identifiers: URICharacter set: UNICODE

Figure 12.1 the Semantic Web stack. oWL = ontology Web Language; RDF =
Resource Description Framework; RiF = Rule interchange Format; SPARQL =
Sparql Protocol and RDF Query Language; SWRL = Semantic Web Rule Language;
URi = Uniform Resource identifier.

Semantic Web. The principal goal of RDF is to add semantics on top of data and
documents.
In RDF, data are expressed and defined by means of RDF statements that, in
the RDF terminology, are often called triples . Triples are in the form of <subject,
proper t y, object> . The subjects denote resources, which are expressed by uniform
resource identifiers (URIs) and represent mainly data and documents. Resources
can have relationships that are defined using specific properties of a vocabulary.
In this way, properties (also called predicates) are typed links with a precise mean-
ing; it is therefore possible to express certain semantics within the data. Properties
can also connect resources to literal values, that is, descriptive character strings.
Accordingly, a resource is described by all its connections and relationships. The
RDF framework allows users to combine triples coming from different sources:
This provides more information than the separate triples do. Consequently, with
metadata and representation of web resources, RDF can enable semantic interoper-
ability across multiple different applications.
A set of RDF triples is called an RDF graph. The nodes of the graph are the
subjects (resources) and the objects (resources or literals); the edges connecting the
nodes are the predicates (properties) between them. The collection of all existing
RDF statements can be seen as a giant RDF database represented in the form of a
directed graph, that is, the previously mentioned web of data.