Journal of Computing, Volume 2, Issue 6, June 2010, ISSN 2151-9617 HTTPS://SITES.GOOGLE.COM/SITE/JOURNALOFCOMPUTING/ WWW.JOURNALOFCOMPUTING.ORG 167 progressed to the Ontology Inference Layer 
(OIL), and continued with the creation of DAML+OIL, the result of joining the American proposal DAML-ONT5 with the European language OIL. All these languages are XML or RDF syntax based, and are consequently compatible with web standards. Indeed, RDF 
and OWL make searching for and reusing information both more reliable and easier, because they are considered as standards that enable the Web to be a global infrastructure for sharing documents and data equally. 

As mentioned in [2], some important requirements for quality support should be taken into account when developing languages for encoding Ontologies. These include giving the user explicit written format, ease of use, expressive power, compatibility, sharing and versioning, internationalisation, formal conceptualisations of domains models, well defined syntax and semantics, efficient reasoning support, sufficient expressive power, and convenience of expression. 

 Syntax is one of the most important features in any language, so it should be well-defined, it is also the most significant condition required for the processing of information by machine. 

 The semantics of knowledge should be well defined because it represents the meaning of that knowledge. Formal semantics should be established in the domain of mathematical logic in, clearly defined way that will lead to unambiguous meaning. Well-defined semantics will lead to correct reasoning. Semantics can be considered as pre- requisites that help to support reasoning. On the other hand, reasoning will help to check and discover consistent Ontology, to verify unintended relationships between classes, and to classify individuals into classes. 

This paper has detailed the most common and important languages such as RDF, RDF/S, DAML+OIL, OWL, all of which are based on XML. 

Extensible Markup Language (XML) [16] is widely known in the WWW community because it is a flexible text format and was designed to describe data and to meet the challenges of largescale e-business and electronic publishing, and it plays an important role in exchanging different type of data on the Web. In fact, it is the basis for a rapidly growing number of software development activities. 

The present research, for the sake of simplicity, deals with RDF and RDFS as one description language. 

## 2 Resource Description Framework (Rdf)

Resource Description Framework (RDF) [3, 4, and 5] a language used to provide a standard for metadata about the resources on the web, is capable of representing data on and exchanging knowledge over the Web. It was developed to be understood by computers, facilitating interoperability between applications. In other words, it is a framework for using and representing metadata and describing the semantics of information about web resources in a way accessible to machines. 

RDF is recommended by the World Wide Web Consortium (W3C). Uniform Resource Identifiers 
(URIs) are the method used by RDF to identify resources or thing. In fact, it is based built upon XML, but while that is designed for syntax, RDF 
is intended for semantics. 

As has been mentioned, RDF is a framework for describing web resources, which is why it has become a common method of describing the properties, time, information and content of web resources, so that it can be read and understood by computer applications. 

RDF can be used in several applications, one of the most important being resource discovery, used to enhance search engine capabilities. It is also used to facilitate knowledge sharing and exchange in intelligent software agents so-called Ontology, and, previously mentioned, to describe the content and content relationships available with any resource such as a page. 

The RDF model has three elements: a resource 
(the subject), the object and the predicate. We can say that <subject> has a property <predicate> valued by <object>. 

For example, a triplet could be "H.ZEDAN is the Head of the STRL Group". In an RDF graph, all triplets "nodes and arcs" should be labelled with qualified URIs. In this example, it could be said that the Subject (Resource) is the STRL Group, the predicate (property) is Head of, and the Object (literally) is H.ZEDAN. 

## 2.1 **Resource Description Framework** (Rdf) **Schema**

The Resource Description Framework / 
Schema (RDFS) [6, 7] has been built upon the XML and RDF models and upon syntax. RDFS 
provides additional facilities to support evolution in both of the individual RDF vocabularies, and the core RDF Schema vocabulary. 

The RDF Schema provides a machineunderstandable system for defining the vocabularies needed for such applications or descriptive vocabularies. In other words, the RDF Schema is a collection of RDF resources that can be used to define or describe properties of other RDF resources which define applicationspecific RDF vocabularies. At the same time, RDF(S) helps developers to describe classes and properties in a specific way and to specify 