A Theory for a Semantic-based Search Service

We illustrate a new approach to the formulation and processing of queries to search digital libraries built re-using and integrating pre-existing heterogeneous information sources. This approach provides a better support for unified search by enhancing the capability of the digital library to satisfy the user needs. The paper presents the theory underlying the proposed approach and describes how we exploit semantic information in the metadata formats and controlled vocabularies produced by information sources locally, and usually discarded by current digital libraries systems.