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

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

This technical report will also appear in A.K. Elmagarmid (ed.): Advanced Transaction Models for New Applications, Morgan Kaufmann Publishers, 1991. Contents 7 The ConTract Model 1

One of the potential benefits of distributed systems is their use in providing highly-available services that are likely to be usable when needed. Availabilay is achieved through replication. By having inore than one copy of information, a service continues to be usable even when some copies are inaccessible, for example, because of a crash of the computer where a copy was stored. This paper presents a new replication algorithm that has desirable performance properties. Our approach is based on the primary copy technique. Computations run at a primary. which notifies its backups of what it has done. If the primary crashes, the backups are reorganized, and one of the backups becomes the new primary. Our method works in a general network with both node crashes and partitions. Replication causes little delay in user computations and little information is lost in a reorganization; we use a special kind of timestamp called a viewstamp to detect lost information. 1

The Coordinated Atomic Action (or CA action) concept is a unified scheme for coordinating complex concurrent activities and supporting error recovery between multiple interacting objects in a distributed object-oriented system. It provides a conceptual framework for dealing with different kinds of concurrency and achieving fault tolerance by extending and integrating two complementary concepts --- conversations and transactions. Conversations (enhanced with concurrent exception handling) are used to control cooperative concurrency and to implement coordinated error recovery whilst transactions are used to maintain the consistency of shared resources in the presence of failures and competitive concurrency. This paper explains the CA action concept in detail and then addresses related design issues such as multi-thread coordination, exception handling and resolution, coordinated access to shared objects and provision of software fault tolerance. Finally, brief details are given of a numb...

Workflow management systems (WFMSs) coordinate the execution of applications distributed over networks. In WFMSs, data inconsistencies can arise due to (i) the interaction between steps of concurrent threads within a workflow (intra-workflow coordination) (ii) the interaction between steps of concurrent workflows (interworkflow coordination) and (iii) the presence of failures. Since these problems have not received adequate attention, this paper focuses on developing the necessary concepts and infrastructure to handle them. First, to deal with inter- and intra- workflow coordination requirements we have identified a set of high level building blocks. Secondly, to handle failures we propose a novel and pragmatic approach called opportunistic compensation and re-execution that allows a workflow designer to customize workflow recovery from correctness as well as performance perspectives. Thirdly, based on these concepts we have designed a workflow specification language that expresses ne...

One primary difference between transactions in an engineering design environment and those in conventional business applications is that an engineering transaction typically lasts a much longer time. Existing proposals for supporting the long-lived engineering transactions are all based on the public/private database architecture, in which a transaction checks out design objects from the public database, modifies them, and checks them into the public database for use by other transactions. However, the design environment which these proposals model is a very rigid one which does not allow a team of designers to complete a complex design involving numerous design objects by passing incomplete objects back and forth among them in a controlled manner. In this paper we present a model of engineering transactions which attempts to resolve this shortcoming as well as satisfying the constraints imposed by the engineering design environment. The model augments existing models by refining the notion of checkout environment which a transaction sees and coupling it with the notion of nested transactions. The model is then extended to a practical mechanism for supporting a complex engineering design environment by imposing the view that a long-lived engineering transaction is really a sequence of conventional short-lived transactions. 1.

This chapter surveys extended transaction models proposed to support long duration, interactive and/or cooperative activities in the context of multi-user software development and CAD/CAM environments. Many of these are variants of the checkout model, which addresses the long duration and interactive nature of the activities supported by environments but still isolates environment users, making it difficult for them to collaborate while their activities are in progress. However, a few cooperative transaction models have been proposed to facilitate collaboration, usually while maintaining some guarantees of consistency.

. Commitments are crucial to understanding and designing autonomous agents and multiagent systems. We propose a definition of commitments that applies especially well to agents in information-rich applications, such as electronic commerce and virtual enterprises. Our approach has a number of important features, including -- not gratuitously translating social concepts to psychological concepts -- distinguishing between satisfied and inapplicable commitments -- incorporating social policies to handle the creation, satisfaction, and cancelation of commitments -- relating commitments to organizational structure in a multiagent system -- showing how commitments are acquired by agents as a consequence of adopting a role. 1 Introduction Commitments are central to DAI. In this paper, "commitment" refers to social, not psychological, commitment. Commitments have drawn much research attention because they are an important abstraction for characterizing, understanding, analyzing, and desig...

SoCom # 1 "on time" Abstract SoCom # 2 "cheap" Buyer Seller Abstract SoCom # 3 Buyer Seller SoCom Manager Hoosier Inc. Register me as buyer and seller Register me as buyer and seller Play Seller in AbstractSoCom #1? Yes Valvano & Co. Hot Air Bros. 8 9 Concrete SoCom created 4 6 7 "high quality" = Roles = Agents Directory Agent_id Role derived 1 Figure 2. Instantiation of a concrete SoCom 68 March 1999/Vol. 42, No. 3 COMMUNICATIONS OF THE ACM Adopt role Need to initiate Ask SoCom manager Participate No No No No No No No Ye s Yes Ye s Yes Yes Yes Ye s Register SoCom manager suggests a socom Request to create SoCom Process request Stop Stop (undefined) Stop (Failure) Instantiate and announce Receipt of a request Request to register Condition evaluation OK? Find candidates Ask candidates All say yes? Agents decision making SoCom manager's decision making Because our agents are autonomous, we must e...