Database systems were a solution to the problem of shared access to heterogeneous files created by multiple autonomous applications in a centralized environment. To make data usage easier, the files were replaced by a globally integrated database. To a large extent, the idea was successful, and many databases are now accessible through local and long-haul networks. Unavoidably, users now need shared access to multiple autonomous databases. The question is what the corresponding methodology should be. Should one reapply the database approach to create globally integrated distributed database systems or should a new approach be introduced?We argue for a new approach to solving such data management system problems, called multidatabase or federated systems. These systems make databases interoperable, that is, usable without a globally integrated schema. They preserve the autonomy of each database yet support shared access.Systems of this type will be of major importance in the future. This paper first discusses why this is the case. Then, it presents methodologies for their design. It further shows that major commerical relational database systems are evolving toward multidatabase systems. The paper discusses their capabilities and limitations, presents and discusses a set of prototypes, and, finally, presents some current research issues.

/pdf/interoperability-of-multiple-autonomous-databases-ol224yhc4e.pdf

Interoperability of multiple autonomous databases

A taxonomy of global information-sharing systems is presented, and the way in which multidatabase systems fit into the spectrum of solutions is discussed. The taxonomy is used as a basis for defining multidatabase systems. Issues associated with multidatabase systems are reviewed. Two major design approaches for multidatabases, global schema systems and multidatabase language systems, are described. Existing multidatabase projects and areas for further research are also discussed. >

A taxonomy and current issues in multidatabase systems

This paper describes the approach to database integration in a heterogeneous distributed database environment utilized by the Amoco Distributed Database System (ADDS). We start with the definition of the extended relational data model that is used by ADDS for database integration. We demonstrate various aspects of resolving possible data conflicts occurring in the database integration process. The ADDS query and data definition languages are defined and their expressive power is discussed. We conclude with presentation of a query conversion algorithm to convert a user data request into a set of queries against supported physical databases.

Database integration in a distributed heterogeneous database system

Publisher Summary Multidatabases integrate the data from preexisting, heterogeneous local databases into a distributed environment, and present global users with transparent methods to use the total information in the system. This chapter describes the taxonomy of global information-sharing systems, multidatabase issues, multidatabse design choices, analysis of existing multidatabase systems, and the position of multidatabase systems in the taxonomy. Multidatabase language systems have no constraints on system size, but the tradeoff for achieving this is a multiple-data-source user paradigm and a more complex user interface. Multidatabase issues, such as site autonomy, differences in data representation, and concurrency control are also discussed in the chapter. Site autonomy is a major strength of multidatabases, yet it is also a major constraint on the global system design. Differences in data representation are many and varied, and resolving these differences is a major concern of the global system design. Global updates are a major current restriction in many systems, and the focus of much current research. To make multidatabase systems more useful and efficient, some deficiencies in existing prototypes must be resolved before they can evolve into commercial products, such as global concurrency control, global security, maintenance and administration, and error control and recovery. Multidatabase systems should begin to have a larger impact in the information-processing world as more powerful systems to become generally available in the near future.

Multidatabase systems : an advanced concept in handling distributed data

The problems of heterogeneous, distinct computer integrated manufacturing (CIM) databases and alternative methods to approach these problems are discussed. The literature in three related areas-natural language (NL) interface for database access, database integration, and CIM data requirements-is reviewed. The architecture of the total system is presented. The detailed design of the NL user interface, which is composed of the DCG (definite clause grammar) parser, the semantic interpreter and the query generator, is described. An experimental prototype of the NL user interface and a demonstration of how the system handles a global NL query are presented. Future issues in the integration of CIM databases are discussed. >

Krzysztof Krajewski

Papers

Architecture of the Network Data Management System.