275
Semantic Technologies for IoT
RDF vocabularies used worldwide are given below:
“Friend of a Friend” (FOAF) (Brickley and Miller 2004) vocabulary is used to represent the relations between entities in social networks.
Dublin Core is used to represent the relations between video, image, and other web
resources.
schema.org is used to describe event, health, and medical types, Organization,
Person, Place, LocalBusiness, Restaurant, etc.
13.2.3 Web Ontology Language
Web Ontology Language (OWL) (Patel-Schneider et al. 2012) is a set of mark-up languages
that are designed for use by applications to process the content of information instead
of just presenting information to humans. The OWL ontology describes the hierarchical
organization of ideas in a domain, in a way that can be parsed and understood by software. OWL has more facilities for expressing meaning and semantics than XML, RDF,
and RDFS, and thus OWL goes beyond these languages in its ability to represent machine
interpretable content on the web. OWL is part of the W3C recommendations related to the
semantic web. It is summarized as follows.
Ontologies are critical for applications that want to search across or merge information
from diverse communities. Although XML DTDs and XML Schemas are sufficient for
exchanging data between parties who have agreed to definitions beforehand, their lack of
semantics prevent machines from reliably performing this task given new XML vocabularies. The same term may be used with different meaning in different contexts, and different
terms may be used for items that have the same meaning. RDF and RDF Schema begin to
approach this problem by allowing simple semantics to be associated with identifiers. With
RDF Schema, one can define classes that may have multiple subclasses and super classes,
and can define properties, which may have subproperties, domains, and ranges. In this
sense, RDF Schema is a simple ontology language. However, in order to achieve interoperation between numerous, autonomously developed and managed schemas, richer semantics
are needed. For example, RDF Schema cannot specify that the Person and Car classes are
disjoint, or that a string quartet has exactly four musicians as members.
OWL adds additional vocabulary for describing properties and relations between classes
and characteristics of properties as depicted in Figure 13.4.
13.2.3.1 OWL Language Basics
OWL offers three expressive sublanguages intended to be use by ontology developers.
• OWL LITE provides users a classification hierarchy and constraints specifications
for classes and properties.
• OWL DL Provides users the most expressive vocabulary including computational
completeness (all conclusions are certain to be computed) and decidability (all
computations can end in finite time).
• OWL Full has most expressiveness and the syntactic freedom of RDF with no
computational guarantees. For example, in OWL Full a class will be treated at
the same time as a collection of individuals and as an individual in its own right.
OWL Full permits an ontology to boost the meaning of the pre-defined (RDF or
OWL) vocabulary.
Semantic Technologies for IoT
RDF vocabularies used worldwide are given below:
“Friend of a Friend” (FOAF) (Brickley and Miller 2004) vocabulary is used to represent the relations between entities in social networks.
Dublin Core is used to represent the relations between video, image, and other web
resources.
schema.org is used to describe event, health, and medical types, Organization,
Person, Place, LocalBusiness, Restaurant, etc.
13.2.3 Web Ontology Language
Web Ontology Language (OWL) (Patel-Schneider et al. 2012) is a set of mark-up languages
that are designed for use by applications to process the content of information instead
of just presenting information to humans. The OWL ontology describes the hierarchical
organization of ideas in a domain, in a way that can be parsed and understood by software. OWL has more facilities for expressing meaning and semantics than XML, RDF,
and RDFS, and thus OWL goes beyond these languages in its ability to represent machine
interpretable content on the web. OWL is part of the W3C recommendations related to the
semantic web. It is summarized as follows.
Ontologies are critical for applications that want to search across or merge information
from diverse communities. Although XML DTDs and XML Schemas are sufficient for
exchanging data between parties who have agreed to definitions beforehand, their lack of
semantics prevent machines from reliably performing this task given new XML vocabularies. The same term may be used with different meaning in different contexts, and different
terms may be used for items that have the same meaning. RDF and RDF Schema begin to
approach this problem by allowing simple semantics to be associated with identifiers. With
RDF Schema, one can define classes that may have multiple subclasses and super classes,
and can define properties, which may have subproperties, domains, and ranges. In this
sense, RDF Schema is a simple ontology language. However, in order to achieve interoperation between numerous, autonomously developed and managed schemas, richer semantics
are needed. For example, RDF Schema cannot specify that the Person and Car classes are
disjoint, or that a string quartet has exactly four musicians as members.
OWL adds additional vocabulary for describing properties and relations between classes
and characteristics of properties as depicted in Figure 13.4.
13.2.3.1 OWL Language Basics
OWL offers three expressive sublanguages intended to be use by ontology developers.
• OWL LITE provides users a classification hierarchy and constraints specifications
for classes and properties.
• OWL DL Provides users the most expressive vocabulary including computational
completeness (all conclusions are certain to be computed) and decidability (all
computations can end in finite time).
• OWL Full has most expressiveness and the syntactic freedom of RDF with no
computational guarantees. For example, in OWL Full a class will be treated at
the same time as a collection of individuals and as an individual in its own right.
OWL Full permits an ontology to boost the meaning of the pre-defined (RDF or
OWL) vocabulary.