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  • Weitere Quellen  (11)
  • 1
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    Imprecise results: Utilizing partial computations in real-time systems (1987)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: In real-time systems, a computation may not have time to complete its execution because of deadline requirements. In such cases, no result except the approximate results produced by the computations up to that point will be available. It is desirable to utilize these imprecise results if possible. Two approaches are proposed to enable computations to return imprecise results when executions cannot be completed normally. The milestone approach records results periodically, and if a deadline is reached, returns the last recorded result. The sieve approach demarcates sections of code which can be skipped if the time available is insufficient. By using these approaches, the system is able to produce imprecise results when deadlines are reached. The design of the Concord project is described which supports imprecise computations using these techniques. Also presented is a general model of imprecise computations using these techniques, as well as one which takes into account the influence of the environment, showing where the latter approach fits into this model.
    Schlagwort(e): COMPUTER PROGRAMMING AND SOFTWARE
    Materialart: NASA-CR-180561 , NAS 1.26:180561
    Format: application/pdf
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  • 2
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    Scheduling real-time, periodic jobs using imprecise results (1987)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: A process is called a monotone process if the accuracy of its intermediate results is non-decreasing as more time is spent to obtain the result. The result produced by a monotone process upon its normal termination is the desired result; the error in this result is zero. External events such as timeouts or crashes may cause the process to terminate prematurely. If the intermediate result produced by the process upon its premature termination is saved and made available, the application may still find the result unusable and, hence, acceptable; such a result is said to be an imprecise one. The error in an imprecise result is nonzero. The problem of scheduling periodic jobs to meet deadlines on a system that provides the necessary programming language primitives and run-time support for processes to return imprecise results is discussed. This problem differs from the traditional scheduling problems since the scheduler may choose to terminate a task before it is completed, causing it to produce an acceptable but imprecise result. Consequently, the amounts of processor time assigned to tasks in a valid schedule can be less than the amounts of time required to complete the tasks. A meaningful formulation of this problem taking into account the quality of the overall result is discussed. Three algorithms for scheduling jobs for which the effects of errors in results produced in different periods are not cumulative are described, and their relative merits are evaluated.
    Schlagwort(e): ADMINISTRATION AND MANAGEMENT
    Materialart: NASA-CR-180562 , NAS 1.26:180562
    Format: application/pdf
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  • 3
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    Producing approximate answers to database queries (1993)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: We have designed and implemented a query processor, called APPROXIMATE, that makes approximate answers available if part of the database is unavailable or if there is not enough time to produce an exact answer. The accuracy of the approximate answers produced improves monotonically with the amount of data retrieved to produce the result. The exact answer is produced if all of the needed data are available and query processing is allowed to continue until completion. The monotone query processing algorithm of APPROXIMATE works within the standard relational algebra framework and can be implemented on a relational database system with little change to the relational architecture. We describe here the approximation semantics of APPROXIMATE that serves as the basis for meaningful approximations of both set-valued and single-valued queries. We show how APPROXIMATE is implemented to make effective use of semantic information, provided by an object-oriented view of the database, and describe the additional overhead required by APPROXIMATE.
    Schlagwort(e): DOCUMENTATION AND INFORMATION SCIENCE
    Materialart: NASA. Lyndon B. Johnson Space Center, The Sixth Annual Workshop on Space Operations Applications and Research (SOAR 1992); p 398-405
    Format: application/pdf
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  • 4
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    PERTS: A Prototyping Environment for Real-Time Systems (1993)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: PERTS is a prototyping environment for real-time systems. It is being built incrementally and will contain basic building blocks of operating systems for time-critical applications, tools, and performance models for the analysis, evaluation and measurement of real-time systems and a simulation/emulation environment. It is designed to support the use and evaluation of new design approaches, experimentations with alternative system building blocks, and the analysis and performance profiling of prototype real-time systems.
    Schlagwort(e): COMPUTER PROGRAMMING AND SOFTWARE
    Materialart: NASA. Lyndon B. Johnson Space Center, The Sixth Annual Workshop on Space Operations Applications and Research (SOAR 1992); p 372-379
    Format: application/pdf
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  • 5
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    Scheduling periodic jobs using imprecise results (1987)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: One approach to avoid timing faults in hard, real-time systems is to make available intermediate, imprecise results produced by real-time processes. When a result of the desired quality cannot be produced in time, an imprecise result of acceptable quality produced before the deadline can be used. The problem of scheduling periodic jobs to meet deadlines on a system that provides the necessary programming language primitives and run-time support for processes to return imprecise results is discussed. Since the scheduler may choose to terminate a task before it is completed, causing it to produce an acceptable but imprecise result, the amount of processor time assigned to any task in a valid schedule can be less than the amount of time required to complete the task. A meaningful formulation of the scheduling problem must take into account the overall quality of the results. Depending on the different types of undesirable effects caused by errors, jobs are classified as type N or type C. For type N jobs, the effects of errors in results produced in different periods are not cumulative. A reasonable performance measure is the average error over all jobs. Three heuristic algorithms that lead to feasible schedules with small average errors are described. For type C jobs, the undesirable effects of errors produced in different periods are cumulative. Schedulability criteria of type C jobs are discussed.
    Schlagwort(e): ADMINISTRATION AND MANAGEMENT
    Materialart: NASA-CR-183120 , NAS 1.26:183120 , UIUCDCS-R-87-1307 , UILU-ENG-87-1780
    Format: application/pdf
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  • 6
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    Mentat: An object-oriented macro data flow system (1988)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Mentat, an object-oriented macro data flow system designed to facilitate parallelism in distributed systems, is presented. The macro data flow model is a model of computation similar to the data flow model with two principal differences: the computational complexity of the actors is much greater than in traditional data flow systems, and there are persistent actors that maintain state information between executions. Mentat is a system that combines the object-oriented programming paradigm and the macro data flow model of computation. Mentat programs use a dynamic structure called a future list to represent the future of computations.
    Schlagwort(e): COMPUTER PROGRAMMING AND SOFTWARE
    Materialart: NASA-TM-101165 , NAS 1.15:101165
    Format: application/pdf
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  • 7
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    Scheduling periodic jobs that allow imprecise results (1990)
    In:  Other Sources
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    Publikationsdatum: 2019-07-12
    Beschreibung: The problem of scheduling periodic jobs in hard real-time systems that support imprecise computations is discussed. Two workload models of imprecise computations are presented. These models differ from traditional models in that a task may be terminated any time after it has produced an acceptable result. Each task is logically decomposed into a mandatory part followed by an optional part. In a feasible schedule, the mandatory part of every task is completed before the deadline of the task. The optional part refines the result produced by the mandatory part to reduce the error in the result. Applications are classified as type N and type C, according to undesirable effects of errors. The two workload models characterize the two types of applications. The optional parts of the tasks in an N job need not ever be completed. The resulting quality of each type-N job is measured in terms of the average error in the results over several consecutive periods. A class of preemptive, priority-driven algorithms that leads to feasible schedules with small average error is described and evaluated.
    Schlagwort(e): COMPUTER PROGRAMMING AND SOFTWARE
    Materialart: IEEE Transactions on Computers (ISSN 0018-9340); 39; 1156-117
    Format: text
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  • 8
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    Issues in the Imprecise Computation Approach to Fault Tolerance (1991)
    In:  CASI
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: The imprecise computation technique can be used in a natural way to enhance fault tolerance. By providing a usable, approximate result whenever a failure or overload prevent the system from producing the desired, precise result, we can increase the availability of data and services, reduce the need for error-recovery operations, and minimize the costs in replication. This paper describes the domain-specific fault tolerance mechanisms that are needed to support the provision and correct usage of imprecise results for several representative application domains. The elements of an application-domain-independent architecture that can effectively integrate these domain-specific mechanisms are also described.
    Schlagwort(e): Computer Programming and Software
    Materialart: System Design Synthesis Technology Workshop; Sep 01, 1991; Silver Spring, MD; United States
    Format: text
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  • 9
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    An Object-oriented Query Processor that Produces Monotonically Improving Approximate Answers (1991)
    In:  CASI
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: The paper describes an object-oriented query processor that makes approximate answers available if there is not enough time to produce an exact answer or if part of the database is unavailable. The accuracy of the approximate result produces improves monotonically with the amount of data retrieved to produce the result. The query processing algorithm is based on an approximate relational data model and works within a standard relational algebra framework. The query processor maintains an object-oriented view on an underlying level and can be implemented on a relational database system with little change to the relational architecture. We show how a monotone query processing strategy can be implemented, making effective use of semantic information presented by the object-oriented view.
    Schlagwort(e): Computer Programming and Software
    Materialart: NASA Review of ICLASS; NASA-CR-202191|Data Engineering; Apr 01, 1991; Kobe; Japan
    Format: text
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  • 10
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    PERTS: A Prototyping Environment for Real-Time Systems (1991)
    In:  CASI
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: We discuss an ongoing project to build a Prototyping Environment for Real-Time Systems, called PERTS. PERTS is a unique prototyping environment in that it has (1) tools and performance models for the analysis and evaluation of real-time prototype systems, (2) building blocks for flexible real-time programs and the support system software, (3) basic building blocks of distributed and intelligent real time applications, and (4) an execution environment. PERTS will make the recent and future theoretical advances in real-time system design and engineering readily usable to practitioners. In particular, it will provide an environment for the use and evaluation of new design approaches, for experimentation with alternative system building blocks and for the analysis and performance profiling of prototype real-time systems.
    Schlagwort(e): Computer Programming and Software
    Materialart: System Design Synthesis Technology Workshop; Sep 01, 1991; Silver Spring, MD; United States
    Format: text
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