Ontology can be reused and shared throughout the application and the concept of groups in the ontology are usually organized in taxonomies and relations between concepts, concept properties, and axioms are usually used to represent the knowledge contained in ontology. on the WWW, they are popular applied in knowledge management, semantic Web, natural language generation, enterprise modeling, knowledge-based systems, ontology-based broker of e-commerce platforms and interoperability between systems. * Are the principles for building an ontology? * What methodologies should I use to build their own ontology? * How does the software supports the process of building and using ontologies? This book presents the theoretical foundations of ontological engineering and covers the practical aspects of selecting and applying methodologies, tools and languages for ontology building. Application ontologies are also illustrated with case studies taken from the field of knowledge management, e-commerce and web semantics.