This survey characterizes an emerging research area, sometimes called coordination theory, that focuses on the interdisciplinary study of coordination. Research in this area uses and extends ideas about coordination from disciplines such as computer science, organization theory, operations research, economics, linguistics, and psychology. A key insight of the framework presented here is that coordination can be seen as the process of managing dependencies among activities. Further progress, therefore, should be possible by characterizing different kinds of dependencies and identifying the coordination processes that can be used to manage them. A variety of processes are analyzed from this perspective, and commonalities across disciplines are identified. Processes analyzed include those for managing shared resources, producer/consumer relationships, simultaneity constraints, and tank/subtask dependencies. Section 3 summarizes ways of applying a coordination perspective in three different domains: (1) understanding the effects of information technology on human organizations and markets, (2) designing cooperative work tools, and (3) designing distributed and parallel computer systems. In the final section, elements of a research

In this paper, a terminological framework is provided for describing different transaction-oriented recovery schemes for database systems in a conceptual rather than an implementation-dependent way. By introducing the terms materialized database, propagation strategy, and checkpoint, we obtain a means for classifying arbitrary

This is the nineteenth edition of a (usually) quarterly column that covers new developments in the theory of NP-completeness. The presentation is modeled on that used by M. R. Garey and myself in our book ‘‘Computers and Intractability: A Guide to the Theory of NP-Completeness,’ ’ W. H. Freeman & Co., New York, 1979 (hereinafter referred to as ‘‘[G&J]’’; previous columns will be referred to by their dates). A background equivalent to that provided by [G&J] is assumed, and, when appropriate, cross-references will be given to that book and the list of problems (NP-complete and harder) presented there. Readers who have results they would like mentioned (NP-hardness, PSPACE-hardness, polynomial-time-solvability, etc.) or open problems they would like publicized, should

Concurrency control has been thoroughly studied in the context of traditional database applications such as banking and airline reservations systems. There are relatively few studies, however, that address the concurrency control issues of advanced database applications such as CAD/CAM and software development environments. The

A partition occurs when functioning sites in a distributed system are unable to communicate. This paper introduces a new method for managing replicated data objects in the presence of partitions. Each operation provided by a replicated object has a set. of quorums, which are sets of sites whose cooperation suffices to execute the operation. The method permits an object’s quorums to be adjusted dynamically in response to failures and recoveries. A transaction that is unable to progress using one set of quorums may switch to another, more favorable set, and transactions in different. partitions may progress using different sets. This method has three novel aspects: (1) it supports a wider range of quorums than earlier proposals, (2) it, scales up effectively to large systems because quorum adjustments do not require global reconfiguration, and (3) it, systematically exploits the semantics of typed objects to support more flexible quorum adjustment.

Interactive systems, such as editors and program development environments, should explicitly support facilities that permit a user to reverse the effects of past actions and to restore an object to a prior state. A model for interactive systems that allows such recovery facilities to be defined precisely and user and system responsibilities to be delineated is presented. Various techniques for implementing recovery are described. Application of a general recovery facility to support reverse execution is discussed. A program development system (called COPE} with extensive recovery facilities, including reverse execution, is described.

In addition to satisfying data consistency requirements as in conventional database systems, concurrency control in real-time database systems must also satisfy timing constraints, such as deadlines associated with transactions. Concurrency control for a real time database system can be studied from several different perspectives. This largely depends on how the system is specified in terms of data consistency requirements and timing constraints. The objective of this research is to investigate and propose concurrency control algorithms for real time database systems, that not only satisfy consistency requirements but also meet transaction timing constraints as much as possible, minimizing the percentage and average lateness of deadline-missing transactions.

We propose an architecture for Digital Library Repositories that assures long-term archival storage of digital objects. The architecture is formed by a federation of independent but collaborating sites, each managing a collection of digital objects. The architecture is based on the following key components: use of signatures as object handles, no deletions of digital objects, functional layering of services, the presence of an awareness service in all layers, and use of disposable auxiliary structures. Long-term persistence of digital objects is achieved by creating replicas at several sites. KEYWORDS: Digital Library Repository, Archival, Longterm Preservation of Data. 1 INTRODUCTION A digital library repository (DLR) stores the digital objects that constitute the library. The two key requirements that distinguish DLRs from other information stores are archival storage and intellectual property management. The archival nature of a DLR means that the digital objects (e.g., documents...

In spite of the wide variety of concurrency control and recovery mechanisms proposed during the past decade, the behavior and the performance of various concurrency control and recovery mecha-nisms remain largely not well understood. In addition, although concurrency control and recovery mechanisms are intimately related, the interaction between them has not been adequately explored. In this paper, we take a unified view of the problems associated with concurrency control and recovery for transaction-oriented multiuser centralized database management systems, and we present several integrated mechanisms. We then develop analytical models to study the behavior and compare the performance of these integrated mechanisms, and we present the results of our performance evalua-tion.

There are several consistency control algorithms for managing replicated files in the face of network partitioning due to site or communication link failures. In this paper, we consider the popular voting scheme along with three enhancements: voting with a primary site, dynamic voting, and dynamic voting with linearly ordered copiee. We develop a stochastic model which compares the file availabilities afforded by each of these schemes. We show that in this model dynamic voting with linearly ordered copies provides the greatest availability. I.