Ontologies are widely used in knowledge engineering, artificial intelligence; as well as applications related to knowledge management, information retrieval and the semantic web. Among the first definition of ontology was provided by Neches et al. [2]; which said that "an ontology defines the basic terms and relations comprising the vocabulary of a topic areas as well as the rules for combining terms and relations to define extensions of the vocabulary". However, the most quoted definition of ontology is based from Gruber [3]; which defined it as "an explicit specification of a conceptualization". Although, there has been no universal consensus for the definition of ontology; the aim of ontology is very clear as put forward by Gomez-Perez et al. [4] that is "to capture consensual knowledge in a generic way, and that they may be reused and shared across software applications and by groups of people". What considered as an ontology is still a debatable issue. Lassila&McGuinness [5] provides a broad categorization ontology, of which can be categorized as lightweight and heavyweight ontology. The ACM topic hierarchy used in this study can be referred to as a lightweight ontology