Event Ontology And Its Application In Query Expansion

Ontology reflects the essence of objects or phenomenon through defining concepts and their relations explicitly. Ontology has become an advanced technology for artificial intelligence and knowledge engineering, which plays an increasingly important role in the representation, acquisition and application of knowledge. Therefore, many research institutions at home and abroad have launched extensively theoretical research and application exploration.Recently, the'event'has been applied to computational linguistics, artificial intelligence, information retrieval, information extraction, automatic summarization and natural language processing. The various texts such as novel, biography, memoir, myth and legend, folktale, epic, drama, press, and so on, include lots of events. An event identified by event triggers is associated with participants, time, location, etc, which is a larger knowledge unit than a concept.The human have suffered and have been suffering all kinds of emergency, including earthquakes, volcanic eruptions, floods, hurricanes, chemical spills, nuclear radiation escape, diseases, accidents, explosions, urban fires, etc. Because an important event in the real world is always reflected on the network in different styles, getting event information has become the key component for the users. With an overwhelming volume of information currently available, the results returned by universal search engine are often informative and inaccurate, and users'experiences of searching are not very good. It is more so for the retrieval of events. So it is urgent to study and develop the event-oriented retrieval technology.The work surrounds event ontology and its application in query expansion in this paper. First, we study the relations of event classes and the association of event classes, and propose an event-oriented ontology model. Then, event is applied in query expansion area, and we explore the methods of query expansion based on pseudo relevant feedback and event ontology. The main contents and innovations of this paper include:(1) Define the concept of event class, analyze the relations of event classes according to the action element of the event class and the relations of event instances according to the object, time and environment elements of the event class. Define the influence factor between event classes to depict the probability by that if an event instance occurred, the other event instance occurs too. Improve an event-oriented ontology model on the basis of the event class, the event class relation and the event class influence factor.(2) Select a sub-area of emergency to study the method of constructing event ontology. Analyze the distinctions of dynamic event and static concept. Put forward a method of computing the importance of events, which synthetically considers both the hubs and authorities of events, denoted by HARank (Hubs-Authorities Rank), and apply the HARank to identify important events from the collection of texts and rank event classes for event ontology.(3) Propose the technology of event-oriented query expansion aiming at the requirements of getting event information. First, present the method of event-oriented query expansion based on pseudo relevant feedback, including the identification of events from texts, the discrimination of qualified terms and event terms of query terms, the selection of expansion events, the setting of query term weights and the similarity computation between query terms and texts. Second, present the method of event-oriented query expansion based on event ontology, including the identification of event terms of query terms based on event ontology, and the associative expansions from event terms of query terms to event classes of event ontology and from the event class to its elements.