Xin Lu

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The purpose of this research is to design a document retrieval model which is a structural model based on case relations and to test how effectively a prototype of this model would perform retrieval on a test database. Case relations are a major component of case grammar proposed by linguistic theorists and developed in computational linguistics and natural language processing.;The design of the structural retrieval model involves case relations and structured document representation, case relation-based natural language parsing and automatic structural indexing, and tree mapping and structural matching. In this model, a document is represented by a set of tree-like case frames in which the components of a natural language clause are assigned to different nodes called cases, and all nodes have pre-defined case relations to the verb of the clause.;To implement such a structural representation by automatic means, an indexing engine was coded (using PROLOG) and developed which consists of a natural language parser and a case frame generator. In response to a natural language query, the prototype of the model (1) processes and converts the query into a set of case frames; (2) measures the structural closeness between the query and every document in a database through tree-mapping; and (3) presents the retrieved documents, according to their closeness to the query, in ranked order.;A number of typical retrieval experiments have been designed to compare the structural model with the vector space model and the Boolean model. All of the model prototypes processed a set of thirty queries on a test database of 534 documents. The retrieval performance was measured using recall-precision graphs, averaged recall and precision, and statistical tests. The experimental results showed that the effectiveness of the structural model was barely comparable to that of the other models. The conclusions are: (1) the structural model is not more effective than other models, and (2) replications of this study are needed to further prove or disprove the usefulness of case relations in improving retrieval effectiveness.



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