Ontology-Based Query Processing for Global Information Systems

This work is a revision of the doctoral dissertation of Eduardo Mena pre­ sented to the Department of Computer Science and System Engineering at the University of Zaragoza (Spain) in November 1998 [Mena 98]. The OBSERVER system was developed as a result of this Ph.D. thesis. This book is composed of eight chapters. In Chapter 1 we introduce our rationale for writing a book about systems that process queries in global information systems. Then in Chapter 2 we review the techno­ logical context for our work, including distributed and heterogeneous environments and the use of ontologies. We also compare related work to our own. Chapter 3 presents our proposed global system architecture for query processing in global information systems. The main modules in the architecture and the main steps given to process a query are briefly introduced. Chapters 4 through 7 provide a detailed description of each query processing step. In Chapter 4 we detail the steps needed to access the data corre­ sponding to a query formulated over an ontology. All the aspects related to distribution, structural and semantic heterogeneity, and restricted query capabilities of the underlying data repositories are considered in this chapter. The main features of the mapping information that relates ontologies and data repositories are also described. Finally, we show the process of generating appropriate plans to access each involved reposi­ tory and the correlation of the answers coming from different reposito­ ries.

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.