Distributed database technology is expected to have a significant impact on data processing in the upcoming years. With the introduction of commercial products, expectations are that distributed database management systems will by and large replace centralized ones within the next decade. In this paper, we reflect on the promises of distributed database technology, take stock of where we are, and discuss the issues that remain to be solved. We also highlight new research issues that arise with the introduction of new technology and the subsequent relaxation of some of the assumptions underlying current systems.

We define mixed fragmentation as a process of simultaneously applying the horizontal and vertical fragmentation on a relation. It can be achieved in one of two ways: by performing horizontal fragmentation followed by vertical fragmentation or by performing vertical fragmentation followed by horizontal fragmentation. The need for mixed fragmentation arises in distributed databases because database users usually access subsets of data which are vertical and horizontal fragments of global relations and there is a need to process queries or transactions that would access these fragments optimally. We present algorithms for generating candidate vertical and horizontal fragmentation schemes and propose a methodology for distributed database design using these fragmentation schemes. When applied together these schemes form a grid. This grid consisting of cells is then merged to form mixed fragments so as to minimize the number of disk accesses required to process the distributed transactions....

this paper, we present an overview of the distributed DBMS and parallel DBMS technologies, highlight the unique characteristics of each, and indicate the similarities between them. This discussion should help establish their unique and complementary roles in data management. Underlying Principles

Distributed database technology is expected to have a significant impact on data processing in the upcoming years. With the introduction of commercial products, expectations are that distributed database management systems will by and large replace centralized ones within the next decade. In this paper, we reflect on the promises of distributed database technology, take stock of where we are, and discuss the issues that remain to be solved. We also present new research issues, such as distributed object-oriented systems, distributed knowledge bases, multiprocessor data servers, and distributed multidatabase systems, that arise with the introduction of new technology and the subsequent relaxation of some of the assumptions underlying current systems. Keywords: distributed database, data distribution, transaction management, distributed query procesing, object-oriented system, knowledge base, multidatabase system. * An abridged version of this paper has appeared as "Distributed Databas...

Process-centered software engineering environments (PSEEs) generate and maintain a significant amount of information in their support of large-scale software development. This paper explores the issues involved in their management of the information. The architectures of most existing PSEEs include a repository that stores product data or process enactment data or both. Different PSEEs use different types of repository; some use existing database technology, some use special-purpose repositories, and others use structured files. To date, however, there has been little work done to explore how their use of repositories differs from how other systems use them. This paper identifies the requirements imposed by PSEEs on the functional capabilities of a repository, evaluates whether or not existing database technology satisfies these requirements, surveys the role of the repository in the architectures of several existing PSEEs, and presents our experience in using and enhancing repository ...

Abstract--An important design issue in distributed data processing systems is to determine optimal data distribution. The problem requires a tradeoff between time and cost. For instance, quick response time conflicts with low cost. The paper addresses the data distribution problem in this conflicting environment. A formulation of the problem as a non-linear program is developed. An algorithm employing a simple search procedure is presented, which gives an optimal data distribution. An example is solved to illustrate the method.

FICAS, an experimental Flow-based Infrastructure for Composing Autonomous Services, supports a service-composition paradigm that integrates loosely-coupled software components. The software components -- processes managed by independent service providers -- are autonomous services. FICAS employs a distributed data flow that differs markedly from centralized processing adopted by many current service integration frameworks, such as CORBA, J2EE and SOAP. Distributed data flows support direct data exchanges among autonomous services, and thus avoid many performance bottlenecks attending centralized processing. The performance and flexibility of FICAS are further improved by adopting active mediation, which distributes computations within the service framework, and reduces the amount of data traffic significantly by moving computations closer to the data. Several varieties of project management and scheduling software have been aggregated using the FICAS prototype. This demonstration establishes that distributed data flow, combining with active mediation, is more effective and efficient than centralized processing when integrating large engineering software services.

This paper describes an experimental Flow-based Infrastructure for Composing Autonomous Services (FICAS), which supports a service-composition paradigm that integrates looselycoupled software components. For traditional software service composition frameworks, the data-flows and control-flows are centrally coordinated, and the composed service operates as the hub for all data communications. FICAS, on the other hand, employs a distributed data flow approach that supports direct data exchanges among web services. The distributed data flows can avoid many performance bottlenecks attending centralized processing. The performance and flexibility of FICAS are further improved by adopting active mediation, which distributes computations within the service framework, and reduces the amount of data traffic significantly by moving computations closer to the data. A system has been prototyped to integrate several project management and scheduling software applications. The prototype implementation demonstrates that distributed data flow, combining with active mediation, is effective and more efficient than centralized processing when integrating large engineering software services.

this paper, we address the problem of stepwise