1 Introduction. - 1. 1 Rationale. - 1. 2 From Federated DBMSs to the Web. - 1. 3 Overview of the Problem. - 1. 4 Summary. - 2 Technological Context. - 2. 1 Distributed Environments. - 2. 2 Ontologies. - 2. 3 Related Work. - 2. 4 Summary. - 3 Architecture for Query Processing. - 3. 1 A motivating example. - 3. 2 Global Description of the Architecture. - 3. 3 The Ontology Server. - 3. 4 The Interontology Relationships Manager. - 3. 5 The Query Processor. - 3. 6 Summary. - 4 Accessing Underlying Data Repositories. - 4. 1 Logical Schemas Data Repositories and Data Sources. - 4. 2 Mappings: Key to Repository Heterogeneity Encapsulation. - 4. 3 Main Steps in Accessing Underlying Data Repositories. - 4. 4 Correlation. - 4. 5 Presentation. - 4. 6 Summary. - 5 Incremental Query Expansion to Multiple Ontologies. - 5. 1 Integration of User and Target Ontologies. - 5. 2 Plans with No Loss of Information. - 5. 3 Plans with Loss of Information. - 5. 4 Summary. - 6 Estimating the Loss of Information. - 6. 1 Measure of Loss Based on Intensional Information. - 6. 2 Measure of Loss Based on Extensional Information. - 6. 3 Example: Measurement of the Extensional Loss. - 6. 4 Loss for the Correlated Answer Across Ontologies. - 6. 5 Translation with Loss for Roles to Be Projected. - 6. 6 Summary. - 7 The OBSERVER Prototype. - 7. 1 Architecture of the Prototype. - 7. 2 Ontologies: Describing Domains About Bibliographic References. - 7. 3 The Interontology Relationships Manager. - 7. 4 The Query Processor. - 7. 5 The Ontology Server. - 7. 6 Testing OBSERVER: Data Retrieved for the Examples. - 7. 7 Summary. - 8 Summary. - 8. 1 Main Contributions. - 8. 2 Features Missing in Our Approach. Language: English