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.

Klappentext

Today we are witnessing an exponential growth of information accumulated within universities, corporations, and government organizations. Autonomous repositories that store different types of digital data in multiple formats are becoming available for use on the fast-evolving global information systems infrastructure. More concretely, with the World Wide Web and related internetworking technologies, there has been an explosion in the types, availability, and volume of data accessible to a global information system. However, this information overload makes it nearly impossible for users to be aware of the locations, organization or structures, query languages, and semantics of the information in various repositories. Available browsing and navigation tools assist users in locating information resources on the Internet. However, there is a real need to complement current browsing and keyword-based techniques with concept-based approaches. An important next step should be to support queries that do not contain information describing location or manipulation of relevant resources. Ontology-Based Query Processing for Global Information Systems describes an initiative for enhancing query processing in a global information system. The following are some of the relevant features: Providing semantic descriptions of data repositories using ontologies; Dealing with different vocabularies so that users are not forced to use a common one; Defining a strategy that permits the incremental enrichment of answers by visiting new ontologies; Managing imprecise answers and estimations of the incurred loss of information. In summary, technologies such as information brokerage, domain ontologies, and estimation of imprecision in answers based on vocabulary heterogeneity have been synthesized with Internet computing, representing an advance in developing semantics-based information access on the Web. Theoretical results are complemented by the presentation of a prototype that implements the main ideas presented in this book. Ontology-Based Query Processing for Global Information Systems is suitable as a secondary text for a graduate-level course, and as a reference for researchers and practitioners in industry.

Zusammenfassung
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.

Inhalt
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.