The Web Ontology Language (WOL)

Introduction

The Web Ontology Language is a group of data languages for writing ontologies. Ontologies describe taxonomies and classification networks properly. Basically they define the structure of data for various domains. Those include the nouns representing classes of objects and therefore the verbs representing relations between the objects.

Ontologies look like class hierarchies in object-oriented programming. Nonetheless there are numerous critical differences. Class hierarchies are meant to represent structures utilized in ASCII text file that evolve fairly slowly whereas ontologies are meant to represent information on the web and are expected to be evolving almost constantly. Ontologies are characteristically much more flexible. By means of their meant to represent information on the web coming from all kinds of heterogeneous data sources in the same way. Class hierarchies on the contrary have a tendency to to be fairly static and be certain of far less varied and more structured sources of knowledge like corporate databases.

Description

The OWL Web Ontology Language is destined to be used by applications. Those applications need to process the content of data rather than just giving information to humans. OWL straightforwardness better machine interpretability of web page. That is helped by XML,RDF and RDF Schema. It helps by providing additional vocabulary alongside a proper semantics. OWL has three gradually-expressive sublanguages: OWL Lite, OWL DL, and OWL Full.

WL is more expressive than RDFS therein it supports cardinality, richer class relationships, and Descriptive Logic (DL) reasoning. OWL pleasures the thought of classes very differently than object oriented programming languages like Java and Smalltalk. But it is nearly like the way PowerLoom uses concepts. In OWL instances of a category are mentioned as individuals and sophistication membership is decided by a group of properties that allow a DL reasoner to infer class membership of a private .

Ontologies

The data described by an ontology within the OWL family is interpreted as a group of individuals and a group of property assertions which relate these individuals to every other. An ontology consists of a group of axioms which place constraints on sets of people. Therefore the sorts of relationships permitted between them. These axioms delivers semantics by permitting systems to infer additional information. A complete outline to the expressive power of the OWL is given within the W3C’s OWL Guide.

OWL ontologies may import other ontologies. That is an addition of information from the imported ontology to the present ontology.

Species

OWL sublanguages

By different levels of expressiveness, the W3C-recommended OWL specification contains the definition of three variants of OWL. These are ordered by increasing expressiveness as OWL Lite, OWL DL and OWL Full. Each of those sublanguages may be a syntactic extension of its simpler predecessor. the subsequent set of relations hold. Their inverses don’t .

Every legal OWL Lite ontology may be a legal OWL DL ontology.

Every legal OWL DL ontology may be a legal OWL Full ontology.

Every in force OWL Lite inference may be a valid OWL DL conclusion.

Every valid OWL DL conclusion may be a valid OWL Full conclusion.

OWL sublanguages

OWL Lite

OWL Lite was in the beginning planned to support those users primarily needing a classification hierarchy and upfront constraints. For instance , while it helps cardinality constraints, it only allows cardinality values of 0 or 1. It had been wanted that it might be simpler to provide tool support for OWL Lite than its more expressive relatives. Those relative permit fast migration path for systems using thesauri and other taxonomies. Actually, most of the expressiveness constraints kept on OWL Lite amount to little quite syntactic inconveniences: utmost of the constructs available in OWL DL are repeatedly built using complex combinations of OWL Lite features, and is equally expressive because the description logic Development of OWL Lite tools has thus proven to be nearly as difficult in place of development of tools used.

OWL DL

The Web Ontology Language DL is meant to supply the utmost expressiveness possible while retaining computational completeness (either φ or ¬φ holds), decidability and therefore the availability of practical reasoning algorithms. OWL DL includes all OWL language constructs, but they will be used only under certain restrictions for example, number restrictions might not be placed upon properties which are declared to be transitive; and while a category could also be a subclass of the many classes, a category can’t be an instance of another class. OWL DL is therefore, named to its communication by description logic, a field of research that has studied the logics that form the formal foundation of OWL.

OWL Full

OWL Full is founded on a distinct semantics from OWL Lite or OWL DL. It was designed to reservation some compatibility with RDF Schema. For example , in OWL Full a category are often treated simultaneously as a set of people and as a private in its own right; this is often not permitted in OWL DL. OWL Full enables an ontology to strengthen the meaning of the pre-defined vocabulary. OWL Full is undecidable, so no reasoning software is in a position to perform complete reasoning for it.

OWL2 profiles

There are three sublanguages of the language in OWL 2. The OWL 2 EL is a piece that has polynomial time reasoning complexity. OWL 2 QL is meant to allow relaxed access and query to data stored in databases. OWL 2 RL may be a rule subset of OWL 2.

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