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Internet of Things (IoT)
properties or predicates describe relations between resources. For example: “hasLocation,” “hasType,” “hasID,” “deviceID.” The relationship from subject to object is expressed
in a directional way. Properties in RDF are also identified by URIs. Say, for example,
“ hasLocation” can be defined as: http://www.loanr.it/ontologies#hasLocation. RDF statements are called triples because they consist of three elements. An RDF statement has the
following syntax:

Example:
<“Sensor”, Of_Type, “Temperature”>
IRIs, literals, and blank nodes are three different types of nodes in an RDF graph.
The  positional constraints in the RDF are as follows: Predicate must be an URI; subject
must be an URI or blank node; and object must be a URI, blank node, or literal. An RDF
graph is a set of RDF triples. It can be visualized as a directed labeled graph. Each triple
in an RDF graph is represented as a node-arc-node connectivity. Figure 13.2 shows the
structure of RDF graph and Figure 13.3 shows the example of an RDF graph.
13.2.1.2 Internationalized Resource Identifier
An IRI is an Internet standard extended upon the existing URI, and it was published in
RFC 3987 standard (Horrocks et al. 2004). The RDF resources are identified by IRI, which
can appear in the subject, predicate, and object positions of a triple. IRI is in the URL form.
13.2.1.3 Literals
Literals are fixed values. Some examples of literals include strings, dates, and numbers. Literals are related with a data type which allows values to be parsed and
Subject
Object
Predicate
URI
URI
Blank node
URI
Blank node
Literal
FIGURE 13.2
Structure of RDF graph with subject, object and predicate.
Incubator/ssn/ssnx/
ssn#hasSensingDevice>
Incubator/ssn/ssnx/ssn#
Sensor>
5/Incubator/ssn/ssnx/s
sn#SensingDevice>
FIGURE 13.3
Example RDF graph.
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