Description: 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.

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