Ontology based information extraction from text

Information extraction systems employ ontologies as a means to describe formally the domain knowledge exploited by these systems for their operation. The aim of this survey is to study the contribution of ontologies to information extraction systems. We believe that this will help towards specifying a concrete methodology for ontology based information extraction exploiting all levels of ontological knowledge, from domain entities for named entity recognition, to the use of conceptual hierarchies for pattern generalization, to the use of properties and non-taxonomic relations for pattern acquisition, and finally to the use of the domain model itself for integrating extracted entities and instances of relations, as well as for discovering implicit information and detecting inconsistencies.