On the current World Wide Web, most of the information is stored syntactically, i.e., only as data. The information that lies within the data can only be understood by humans and not automatically by computer programs. In order to overcome this issue, the idea of encoding the information not just syntactically but also with semantics has created a new notion of the Web called Semantic Web. This notion emerged together with developments of semi-structured languages like SGML and XML.
Key Terms in this Chapter
Heavyweight Ontology: An ontology of different, but rather higher expressivity, which bases on a formal logic. With such an ontology, it is possible to perform formal reasoning.
Open World Assumption (OWA): The presumption that what is not stated true is unknown and thus cannot be assumed to be either true or false. The OWA is considered being implicit in the Web as new Web sites can be connected and disconnected to the Web at any time.
Syntactic Interoperability: Applications can take advantage of parsers and APIs providing syntactical manipulation facilities. If a language is standardized, it is used actively and required parsers and APIs are implemented.
Lightweight Ontology: An ontology which corresponds rather to a vocabulary and usually does not base on a formal logic.
Closed World Assumption (CWA): The presumption that what is not currently known to be true is false. This assumption introduces nonmonotonicity if the world is not closed, i.e., new information can be introduced or deleted. The opposite of the CWA is the OWA, stating that lack of knowledge does not imply falsity.
Semantic Interoperability: Applications can understand the meaning of representations and thus can setup automatically mappings between different representations by content analysis.
Semantic Web: The next evolutionary step of the World Wide Web. It bases on language standards that provide not only universal expressive power and syntactic interoperability, but also semantic interoperability.
Ontology Language: A formal language used to encode an ontology.
Ontology: A data model that represents the objects, sets of similar objects (i.e., classes), and their interrelations within a domain of discourse.