Research On Ontology-based Semantic Query Techniques

Because of lack of semantics for data and semantic support for the query processing, the key-word-based conventional query only can give information which is matching the condition of users' queries in the syntax layer, but can't get other information which is matching the condition in the semantic layer, so the quality of result of information query is becoming lower. Ontology, which can be used to describe the model of domain's concepts, has good hierarchical-structure of concepts and supports for logical inference, can provide semantic support for information query, for achieving the semantic information query.By analyzing the existing techniques of semantic query and researching on the ontology, and based on the research product of ours, this paper proposes an ontology-based semantic query framework. This framework mainly includes the surroundings, semantic query engine, and semantic query interface; among them, the surroundings includes ontology and database which are separately used to describe knowledge and data of the same domain, and mapping relationships of the elements between ontology and database; the semantic query engine comprises the function modules of query inference and expansion, query reformulation, and semantic wrap. Under the framework, the paper researches on key techniques of ontology-based semantic query which is based on domain ontology (data source ontology) and a single relational database which is semantically labeled by the ontology.On the base of the mapping relationships of the elements between ontology and database(labeled by mapping relationship of Onto-RDB elements) and the rules defined in advance of semantic inference and expansion by using constructor of ontology, firstly this paper builds an ontology-based semantic context query interface, through which user can submit ontology-based semantic query; The module of query inference and expansion uses the rules defined in advance to infer and expand the semantic query, for obtaining a group of semantic queries which have the semantic relationship with the originally semantic query; The module of query reformulation rewrites the ontology-based semantic query to query for relational database by using mapping relationship of Onto-RDB elements, and then submits it to database query engine RDBMS; Finally the module of semantic wrap packs the result of querying database to the semantic result, and displays it through the semantic context query interface, for returning to the user.Finally this paper develops a prototype of an ontology-based semantic query. This prototype takes the domain of literature query as the research object, to realize semantic query for literature information. The result of case study indicates that the technical plan of this paper is effective and feasible.