Peter D. Skopp and Gail E. Kaiser. Disconnected operation in a multiuser software development environment. In Bharat Bhargava, editor, IEEE Workshop on Advances in Parallel and Distributed Systems, pages 146-151, Princeton NJ, October 1993.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....Caubweb s, but still requires the user to specify what is to be cached, using a simple decaying priority algorithm to cache les that are accessed but not speci ed in a hoard pro le, and cannot take into account the le accesses of other users when determining hoard priority. In the Laputa system[11], prefetching is again used to provide a user with access to documents when that user is disconnected from the network. This system lists three types of criteria for determining what documents to prefetch: manual, heuristic, and process based. While manual and heuristic methods are seen in Coda s ....

Peter D. Skopp and Gail E. Kaiser. Disconnected operation in a multiuser software development environment. In Bharat Bhargava, editor, IEEE Workshop on Advances in Parallel and Distributed Systems, pages 146-151, Princeton NJ, October 1993.

....some underlying mechanism for doing it. However, we do address the issue of prefetching data prior to detachment to minimize the adverse impact of the wireless channel on users. The issue of disconnected and low bandwidth operation in the specific context of SDEs has been addressed in detail in ([6, 7]) The work has identified the issues related to the existence of low bandwidth, error prone links in a multiuser SDE and the need for a new model to address the problems. Intelligent prefetching and caching and the use of proxy clients as user agents have been proposed to reduce bandwidth ....

....a valuable contribution in terms of building a complete system within the framework of Oz to solve the various problems. This includes solutions for concurrency control and data reintegration. The work is motivated by the same set of problems as ours but the approaches have been different. While ([6, 7]) has attempted to provide solutions through experiences with a specific SDE, we have been interested in identifying decisions that need to be made for efficient low bandwidth operation. and in building a general framework that is rich and flexible enough for use in different SDEs. There are some ....

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P.D. Skopp, G.E. Kaiser. Disconnected Operation in a Multi-User Software Development Environment. IEEE Workshop on Advances in Parallel and Distributed Systems Oct '93 pp. 146-151.

....for the built in operations. Besides the project aiming to the construction of a new tool integration protocol that is the object of this thesis and to which we gave the name of Rivendell, other new features implemented or planned for Oz are support for disconnected and low bandwidth operation [46], automatic maintenance of user agendas as to do lists [53] delegation of process steps as a collaboration facility between users, and an advanced rule based language for specifying concurrency control policies [24] 4 Related work As we pointed out in the previous sections, tool integration ....

....most general context. For example, the delegation to an SPC of a certain process fragment 16 The design and implementation of this system component has be carried out in close collaboration with Peter Skopp, of the PSL at Columbia University, who has been developing a proxy client for Laputa [46]. The main difference is that an SPC can service different GPCs in their tool related operations while each proxy is dedicated to a single client, as auxiliary in low bandwidth operation. 77 can overcome architectural walls (e.g. it is possible to ask to SPC running on a DEC host to perform a ....

Peter D. Skopp and Gail E. Kaiser. Disconnected operation in a multi-user software development environment. In Bharat Bhargava, editor, IEEE Workshop on Advances in Parallel and Distributed Systems, pages 146--151, Princeton NJ, October 1993. 96

.... permanent , in the sense that its existence is essential for the operation of the client. That is, a client is assumed to always be connected to its local server. An extension of this model, in which clients can be disconnected temporarily from their server, is investigated separately by Skopp [99]. In contrast, the two other connections can be regarded as temporary , since they are 1 There are actually three kinds of clients: XView, Motif, and a command line client. 158 Activity Execution Scheduler Task Clients Local Remote Built in Data Remote Object Cache Storage Locks ....

Peter D. Skopp and Gail E. Kaiser. Disconnected operation in a multi-user software development environment. In Bharat Bhargava, editor, IEEE Workshop on Advances in Parallel and Distributed Systems, pages 146--151, Princeton NJ, October 1993.

....used as the correctness criteria in Thor, cooperative multi user activities are not supported. Instead, it was proposed that sharing of data among multiple users is controlled by the application itself outside the DBMS. The problem of disconnected cooperation among multiple users is addressed in [27] for the special case of software engineering environments. The system described is based on a file repository which includes additional control mechanisms. In contrast to above it uses a checkout model where files have to be locked before caching them at the mobile clients. Two new lock modes are ....

P. D. Skopp and G. E. Kaiser. Disconnected operation in a multi-user software development environment. In Proceedings of the IEEE Workshop on Advances in Parallel and Distributed Systems, October 1993. Princeton, NJ.

....is used as the correctness criteria in Thor, cooperative multiuser activities are not supported. Instead, it was proposed that sharing among multiple users is controlled by the application itself outside the DBMS. The problem of disconnected cooperation among multiple users is addressed in [SK93] for the special case of software engineering environments. The system described is based on a file repository which includes additional control mechanisms. In contrast to above it uses a checkout model where files have to be locked before caching them at the mobile clients. Two new lock modes ....

P. D. Skopp and G. E. Kaiser. Disconnected operation in a multi-user software development environment. In Proceedings of the IEEE Workshop on Advances in Parallel and Distributed Systems, October 1993. Princeton, NJ.

....and algorithms. 2.2 Prefetching The concept of prefetching has been used in a variety of environments including microprocessor designs, virtual memory paging, databases, and file read ahead. More recently, long term prefetching has been used in file systems to support disconnected operation [14, 15, 5]. Prefetching has also been used to improve parallel file access on MIMD architectures [4] One relatively straight forward method of prefetching is to have each application inform the operating system of its future requirements. This approach has been proposed by Patterson et al. 11] Using ....

Peter Skopp and Gail Kaiser. Disconnected Operation in a Multi-User Software Development Environment. In Proceedings of the IEEE Workshop on Advances in Parallel and Distributed Systems, pages 146--151, October 1993.

.... on Database and Expert Systems Applications, September 1996 extensively in the context of network partition [6] The frequency of their occurrence in portable computing, however, forces making them part of normal operation and considering a new mode of operation called disconnected operation [10, 11, 25, 23]. Another characteristic of mobile distributed computing is weak connectivity. Wireless networks deliver much lower bandwidth than wired networks and have higher error rates [8] Finally, mobile systems are characterized by high variation in network bandwidth, that can shift one to four orders of ....

P. D. Skopp and G. E. Kaiser. Disconnected Operation in a Multi-User Software Development Environment. In Proceedings of the IEEE Workshop on Advances in Parallel and Distributed Systems, Princeton, New Jersey, October 1993.

.... and studied in a variety of environments including microprocessor designs, virtual memory paging, databases, and file read ahead [AK96, Mow94, PZ91, Smi78, Smi85] In the context of mobile computing, long term (batch) file prefetching has been used to support disconnected operation [Sat90, SK93, Kue94, KPR94, ABC89, HH93] File system prefetching has long been used to improve intrafile accesses (accesses within a file) Smith [Smi78] and Korner [Kor90] examined the problem of predicting future file block accesses within the current file. Such models can significantly improve access to ....

Peter Skopp and Gail Kaiser. Disconnected Operation in a Multi-User Software Development Environment. In Proceedings of the IEEE Workshop on Advances in Parallel and Distributed Systems, pages 146--151, October 1993.

....has been designed to make network disconnections transparent to the user, by creating on board file caches and by devising techniques for maintaining consistency of shared data. The issue of disconnected and low bandwidth operation in the specific context of SDEs has been addressed in detail in [11, 10]. The work has identified the issues related to the existence of low bandwidth, error prone links in a multiuser SDE and the need for a new model to address the problems. Intelligent prefetching and caching and the use of proxy clients as user agents have been proposed to reduce bandwidth ....

....a valuable contribution in terms of building a complete system within the framework of Oz to solve the various problems. This includes solutions for concurrency control and data reintegration. The work is motivated by the same set of problems as ours but the approaches have been different. While [11, 10] has attempted to provide solutions through experiences with a specific SDE, we have been interested in identifying decisions that need to be made for efficient low bandwidth operation. and in building the core component for a general framework that is rich and flexible enough for use in different ....

[Article contains additional citation context not shown here]

SKOPP, P., AND KAISER, G. Disconnected Operation in a Multi-User Software Development Environment. In IEEE Workshop on Advances in Parallel and Distributed Computing (1993), pp. 146--151.

....system has been designed so that it is largely independent of the underlying replication system. 9.2 Systems for Disconnected Operation Several investigators have built prototype mobile systems based on existing replicated file systems [Alonso et al. . 1990, Huston and Honeyman 1993, Kistler 1993, Skopp and Kaiser 1993, Tait et al. . 1995] However, with the exception of Tait s Spy Utility [Tait et al. . 1995] these systems place most or all of the file specification burden directly on the user. 9.2.1 Coda The first system providing significant support for disconnected operation appears to be Coda [Kistler and ....

....a user s makefiles, although it is not clear whether this idea was ever implemented. This work predates Coda, but it apparently was not carried to fruition, and no usage data of any sort has been reported, so it has had less impact. Finally, a planned system named Laputa was described in [Skopp and Kaiser 1993], though no further results have been published to date. Laputa s hoarding system was not described in great detail, but appeared to incorporate augmented LRU in the manner of Coda, plus a rule based system that used detailed knowledge of the user s work process, possibly generated by a human ....

Peter D. Skopp and Gail E. Kaiser. "Disconnected Operation in a Multi-User Software Development Environment." In Proceedings of the IEEE Workshop on Advances in Parallel and Distributed Systems, Princeton, NJ, October 1993. IEEE.

....test. 6 Related work The concept of prefetching has been used in a variety of environments including microprocessor designs, virtual memory paging, databases, and file read ahead. More recently, long term prefetching has been used in file systems to support disconnected operation [Sat90, SK93, Kue94] Prefetching has also been used to improve parallel file access on MIMD architectures [KE90] Many Unix s perform a type of intra file prefetching known as read ahead. When these operating systems notice that a file is being used sequentially, they cause substantial parts of the file to ....

Peter Skopp and Gail Kaiser. Disconnected Operation in a Multi-User Software Development Environment. In Proceedings of the IEEE Workshop on Advances in Parallel and Distributed Systems, pages 146--151, October 1993.

....in parallel, there is a substantial performance gain compared to centralized execution, as expected. Open questions posed by this research include: 1) Support for multi formalism inter operability on top of our decentralized model; 2) Varying bandwidth has not yet been addressed (although see [24]) 3) Integration of groupware technology into the DEPCE framework, including process support for multiuser tools, and incorporation of multi media technology; 4) Decentralization of concurrency control and recovery policies suitable for collaborative work; and (5) Methodology for defining ....

Peter D. Skopp and Gail E. Kaiser. Disconnected operation in a multi-user software development environment. In IEEE Workshop on Advances in Parallel and Distributed Systems, pages 146--151, October 1993.

.... demand by the Connection Server, as will be explained shortly) 3 An extension of this model, in which clients can be disconnected from their server and continue to operate independently to enact a process segment until reconnection, has been investigated separately to support mobile computing [67]. Activity Execution Clients Built in Commands Remote Object Cache Storage Manager Locks Animation Info Objectbase Display Local Server Client Transactions SubEnv Server Local Remote Remote Servers Rule Processor Local Remote Local Schema Evolver Process Evolver Clients Server Rule Base Class ....

Peter D. Skopp and Gail E. Kaiser. Disconnected operation in a multi-user software development environment. In Bharat Bhargava, editor, IEEE Workshop on Advances in Parallel and Distributed Systems, pages 146--151, Princeton NJ, October 1993. ftp://ftp.psl.cs.columbia.edu/pub/psl/CUCS026 -93.ps.Z.

.... the distinctions are not germane to this paper; see [59, 67, 21] 6 An extension of this model, in which clients can be disconnected from their server and continue to operate independently to enact a process segment until reconnection, has been investigated separately to support mobile computing [60]. Activity Execution Task Clients Local Remote Summit Built in Commands Remote Object Cache Storage Manager Locks Animation Info Objectbase Display Local Server Client Transactions SubEnv Server Local Remote Remote Servers Rule Processor Local Remote Local Schema Evolver Process Evolver Clients ....

....communication bandwidth may be relatively low) Thus, an effective object cache may improve the performance significantly. Another motivation for the cache is to hold pre fetched objects in case a pre fetching mechanism is employed (e.g. based on the semantics of the process model as discussed in [60]) The interesting aspects of the cache implementation from the federated PCE perspective are to address its particular requirements, and to possibly use the semantics of the federated process and data models to direct the cacheinvalidation policy. A typical Oz activity involves a set of related ....

[Article contains additional citation context not shown here]

Peter D. Skopp and Gail E. Kaiser. Disconnected operation in a multi-user software development environment. In Bharat Bhargava, editor, IEEE Workshop on Advances in Parallel and Distributed Systems, pages 146--151, Princeton NJ, October 1993.

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P. D. Skopp and G. E. Kaiser. Disconnected operation in a multi-user software development environment. In Proceedings of the IEEE Workshop on Advances in Parallel and Distributed Systems, October 1993. Princeton, NJ.

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