1 Give a semantic model and build domain ontology for domain knowledge;
2 Pre–process the document, divide it into several fragments in accordance with the integrity of the expressed meaning, and label the fragments;
3 According to the result of assignment, one or several document fragments compose the document object. The global unique identifier and the set of assignment concept are stored in the database as metadata;
4 Optimize and expand the user's query request under the guidance of domain ontology.