| 1. |
- Brand, Per, et al.
(författare)
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A platform for constructing virtual spaces
- 1998. - 1
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Konferensbidrag (refereegranskat)abstract
- Virtual spaces (worlds) applications are among the most complex of distributed applications. They are both distributed and open. Minimizing network latency, fault-tolerance, persistence, resource control, and security are also important aspects. Designing and implementing virtual spaces is currently difficult in that the already not insignificant complexities of program functionality, distribution, openness, and efficiency are interwound and cannot be tackled separately. We present a distributed programming language, distributed-Oz, that greatly reduces the complexity of distributed programming by clearly separating the different aspects of distributed programming. The design and implementation of distributed-Oz is ongoing work, but considerable progress has been made. The current prototype demonstrates network transparency, that computations behave the same way regardless of how the computation is partitioned between different sites. This is the basis for realizing clean separation of the functionality aspect from other aspects. Network awareness allows the programmer to predict and control network communication patterns. The current system gives the programmer the means to tackle separately the aspects of openness, efficiency (minimizing latency), distribution, and functionality. We have extended distributed-Oz with a tool for graphics in a distributed setting. This extends the idea of network transparency and network awareness to graphics. From the programmers point of view graphics programming for a multi-user application is virtually the same as programming for a single-user application. The differences are necessary extensions for achieving network and site awareness, such as visualization control (deciding which users should see what). Finally we consider virtual space applications, and propose a number of abstractions for use by developers of virtual spaces, relating them to the properties of distributed-Oz upon which they are based.
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| 2. |
- Haridi, Seif, et al.
(författare)
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Efficient logic variables for distributed computing
- 1999
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Ingår i: ACM Transactions on Programming Languages and Systems. - : Association for Computing Machinery (ACM). - 0164-0925 .- 1558-4593. ; 21:3, s. 569-626
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Tidskriftsartikel (refereegranskat)abstract
- We define a practical algorithm for distributed rational tree unification and prove its correctness in both the off-line and on-line cases. We derive the distributed algorithm from a centralized one, showing clearly the trade-offs between local and distributed execution. The algorithm is used to realize logic variables in the Mozart Programming System, which implements the Oz language (see http://www.mozart-oz.org). Oz appears to the programmer as a concurrent object-oriented language with dataflow synchronization Logic variables implement the dataflow behavior. We show that logic variables can easily be added to the more restricted models of Java and ML, thus providing an alternative way to do concurrent programming in these languages. We present common distributed programming idioms in a network-transparent way using logic variables. We show that in common cases the algorithm maintains the same message latency as explicit message passing. In addition, it is able to handle uncommon cases that arise from the properties of latency tolerance and third-party independence. This is evidence that using logic variables in distributed computing is beneficial at both the system and language levels. At the system level, they improve latency tolerance and third-party independence. At the language level, they help make network-transparent distribution practical.
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| 3. |
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| 4. |
- Haridi, Seif, et al.
(författare)
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Programming languages for distributed applications
- 1998
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Ingår i: New generation computing. - 0288-3635 .- 1882-7055. ; 16:3, s. 223-261
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Tidskriftsartikel (refereegranskat)abstract
- Much progress has been made in distributed computing in the areas of distribution structure, open computing, fault tolerance, and security. Yet, writing distributed applications remains difficult because the programmer has to manage models of these areas explicitly. A major challenge is to integrate the four models into a coherent development platform. Such a platform should make it possible to cleanly separate an application's functionality from the other four concerns. Concurrent constraint programming, an evolution of concurrent logic programming, has both the expressiveness and the formal foundation needed to attempt this integration. As a first step, we have designed and built a platform that separates an application's functionality from its distribution structure. We have prototyped several collaborative tools with this platform, including a shared graphic editor whose design is presented in detail. The platform efficiently implements Distributed Oz, which extends the Oz language with constructs to express the distribution structure and with basic primitives for open computing, failure detection and handling, and resource control. Oz appears to the programmer as a concurrent object-oriented language with dataflow synchronization. Oz is based on a higher-order, state-aware, concurrent constraint computation model.
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| 6. |
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| 7. |
- Van Roy, Peter, et al.
(författare)
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Mobile objects in distributed Oz
- 1997
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Ingår i: ACM Transactions on Programming Languages and Systems. - : Association for Computing Machinery (ACM). - 0164-0925 .- 1558-4593. ; 19:5, s. 804-851
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Tidskriftsartikel (refereegranskat)abstract
- Some of the most difficult questions to answer when designing a distributed application are related to mobility: what information to transfer between sites and when and how to transfer it. Network-transparent distribution, the property that a program's behavior is independent of how it is partitioned among sites, does not directly address these questions. Therefore we propose to extend all language entities with a network behavior that enables efficient distributed programming by giving the programmer a simple and predictable control over network communication patterns. In particular, we show how to give objects an arbitrary mobility behavior that is independent of the object's definition. In this way, the syntax and semantics of objects are the same regardless of whether they are used as stationary servers, mobile agents, or simply as caches, These ideas have been implemented in Distributed Oz, a concurrent object-oriented language that is state aware and has dataflow synchronization. We prove that the implementation of objects in Distributed Oz, is network transparent. To satisfy the predictability condition, the implementation avoids forwarding chains through intermediate sites. The implementation is an extension to the publicly available DFKI Oz 2.0 system.
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