Showing papers on "Scheduling (computing) published in 1983"

Planning in Time: Windows and Durations for Activities and Goals

Abstract: A general purpose automated planner/scheduler is described which generates parallel plans to achieve goals with imposed time con-straints Both durations and start time windows may be specified for sets of goal conditions The parallel plans consist of not just actions but also of events (triggered by circumstances), inferences, and scheduled events (completely beyond the actor's control) Deterministic dura-tions of all such activities are explicitly modeled, and may be any com-putable function of the activity variables A start time window for each activity in the plan is updated dynamically during plan generation, in order to maintain consistency with the windows and durations of adja-cent activities and goals The plans are tailored around scheduled events The final plan network resembles a PERT chart From this a schedule of nominal start times for each activity is generated Ex-amples are drawn from the traditional blocksworld and also from a real-istic ``Spaceworld,'' in which an autonomous spacecraft photographs objects in deep space and transmits the information to Earth The author is with the Information Systems Research Section, Jet Propulsion Laboratory, Pasadena, CA 91109

Method of scheduling meetings

Abstract: A method of scheduling a meeting among terminal users who are provided with calendaring applications for storing and retrieving timed and dated events. Included is presentation to a meeting scheduler of a prompting screen with blanks for keying in desired times and dates, and prospective attendees. Based on keying to this screen, there is a comparison with the prospective attendees' calendars of events. The result of the comparison is an option list which is presented to the scheduler for selecting an available meeting time. Based on a selection from the option list, a meeting notification screen is built for transmitting to the attendees.

Simple Approaches to Shift, Days-Off and Tour Scheduling Problems

Abstract: Shift and days-off scheduling problems have received much attention in the literature of integer programming approaches to workforce scheduling. A typical managerial use would be to schedule full-time employees to minimize the number of labor hours while satisfying variable workforce requirements of a service delivery system. We present computational experience to show that an easily implemented application of linear programming frequently produces optimal solutions to these problems. When the context progresses toward a continuous operating environment (service delivery over 24 hours a day, 7 days a week) we stress the need to shed the myopic views of the shift and days-off scheduling formulations in favor of an integrative tour scheduling formulation. For this problem we observe that a simple heuristic initiated by rounding down the associated LP solution consistently produces near optimal solutions. This observation is based on experiments over varying workforce requirement patterns.

A Dynamic Model for Strategically Allocating Retail Space

Abstract: The allocation of shelf space is a major determinent of a retailer's sales and operating costs. All the existing models of this problem focus on static optimization. But to the retailer, anticipating and adapting to new tastes and changing product life cycles is the central strategic problem. This paper shows how the static model can be extented to incorporate such market dynamics. The new model is more plausible than earlier static models in encouraging the retailer to allocate more space to new products and divest earlier from declining ones.

Multiprocessor Scheduling of Unit-Time Jobs with Arbitrary Release Times and Deadlines

Abstract: We present a polynomial time algorithm for constructing an optimal schedule, if a feasible schedule exists, for tthe following multimachine scheduling problem. There are n unit-time jobs, with arbitrary release times and deadlines, and m identical parallel machines. A feasible schedule is one in which no job is started before it is released, each job is completed by its deadline, and no job is interrupted once it begins to run.

Technique for dynamic scheduling of integrated circuit- and packet-switching in a multi-beam SS/TDMA system

Abstract: The present invention relates to a technique for dynamic scheduling of integrated circuit- and packet-switching in accordance with rapidly changing demand in a multibeam satellite switched, time division multiple accessed (SS/TDMA) environment. It is equally applicable to terrestrial communication systems, or more broadly to any type of centralized scheduling system involving arbitration of contention for resources among a plurality of users or equipments. All of the scheduling is performed onboard the satellite by a scheduler (6, 8) under the direction of a controller (4). The controller contains all the information related to both circuit requests ([cij ]) and packet requests ([pij ]) in matrix form, where it constructs these matrices from requests for service from each zone to each zone on a frame-by-frame or possibly less frequent basis, which it receives from the ground via an order-wire facility. The scheduler performs, for each of the slots of a frame, a least-choice assignment of the circuit requests contained in the controller. The scheduler then applies the same least-choice procedure to assign packets to switch positions not already assigned to the circuit traffic. The least-choice assignment yields efficient bandwidth and transponder utilization. Provision is also made for prioritizing or preempting both the circuit and packet traffic employing a movable-boundary or other protocols. At the completion of both the circuit and packet assignments for a particular slot, the controller broadcasts the slot schedule to the earth stations.

Application of Decomposition Techniques to the Mid - and Short - Term Scheduling of Hydrothermal Systems

Abstract: This paper describes a methodology for coordinating the mid and short-term scheduling of hydrothermal systems. The technique is able to "translate" the electrical problems at the short-term level into a constraint to be added to the mid-term scheduling problem. This constraint, called a Benders cut, only refers to weekly target variables in the mid-term problem. The Benders decomposition therefore allows a "feedback" between the short-and mid-term models with only a few modifications required in the specialized algorithms used at each level. A case study with the Brazilian Southeast Network is presented and discussed.

Parallel Scheduling Algorithms

Abstract: Parallel algorithms are given for scheduling problems such as scheduling to minimize the number of tardy jobs, job sequencing with deadlines, scheduling to minimize earliness and tardiness penalties, channel assignment, and minimizing the mean finish time. The shared memory model of parallel computers is used to obtain fast algorithms.

Control of a Heterogeneous Two-Server Exponential Queueing System

Abstract: A dynamic control policy known as "threshold queueing" is defined for scheduling customers from a Poisson source on a set of two exponential servers with dissimilar service rates. The slower server is invoked in response to instantaneous system loading as measured by the length of the queue of waiting customers. In a threshold queueing policy, a specific queue length is identified as a "threshold," beyond which the slower server is invoked. The slower server remains busy until it completes service on a customer and the queue length is less than its invocation threshold. Markov chain analysis is employed to analyze the performance of the threshold queueing policy and to develop optimality criteria. It is shown that probabilistic control is sub-optimal to minimize the mean number of customers in the system. An approximation to the optimum policy is analyzed which is computationally simple and suffices for most operational applications.

A decomposition solution to the queueing network model of the centralized DBMS with static locking

Abstract: The effect of concurrency control methods on the performance of computer systems is analyzed in the context of a centralized database with a static lock request policy, i.e., database transactions should acquire all locks before their activation. In the lock conflict model the L locks required by each transaction are uniformly distributed over the N locks in the database. The computer system is modelled as a queueing network. Two scheduling policies for transaction activation are considered: FCFS with and without skip. In each case the scheduling overhead for scanning the blocked transactions is taken into account. The number of transactions to be scanned is limited by a window size parameter. The system is analyzed using a hierarchical decomposition method, where the highest level model yields the mean user response time. The results of the approximate solution are validated using a detailed simulation, which shows that the analysis based on no resampling of locks is quite accurate and outperforms the simplified analysis with resampling of locks in accuracy. The effect of varying the values of parameters such as transaction size, granularity of locking, scheduling discipline for transaction activation, scheduling overhead, and window size on system performance is investigated.

Microcomputer applications

Abstract: Surveys of the use of micros that were made a few years ago suggested that use was concentrated in a few business functions. Calcs and financial reporting packages were expanding in use so rapidly that other types of applications seemed to be unnoticed. However, micros were being introduced in many laboratories and production facilities. A recent survey of departments of companies that use micros reported 98 separate applications that could be grouped under the following organizational areas: accounting, planning, treasurer, purchasing, administration, personnel, operations or production, marketing and otherMost of the applications were financial in nature although operations or production uses were significant. Financial modeling and calc packages were used not only in financial applications, but they were also used develop a master scheduling job for manufacturing and for administrative and planning applications. Word processing packages were also used to handle many different jobs such as promotion, scheduling, tracking of assignments and automatic editing of information accessed from data bases. Packages are used quite often with micros as generalized development tools. This results in interesting support problems.Applications of micros can also be considered in terms of the data communication involved. Most uses of micros have been on a stand alone basis, but an increasing number of applications involve communication with another micro or a host computer. The micro may be an intelligent terminal controlled by the host or it may be directing the other computing system. The micro may also transfer control back and forth to the other system in an integrated application.

Scheduling a Single Machine to Minimize the Weighted Number of Tardy Jobs

Abstract: In this paper the problem of scheduling jobs on a single machine to minimize the weighted number of tardy jobs is examined. It contains the framework for a new branch-and-bound procedure as well as the first extensive computational study of the problem. Results indicate that large problems, e.g. 50 jobs, can be solved in just a few seconds of computer time. Further, the computational results provide insight into how various problem parameters affect the solution difficulty of particular problems.

Scheduling file transfers in a distributed network

Abstract: We consider a problem of scheduling file transfers in a network so as to minimize overall finishing time, which we formalize as a problem of scheduling the edges of a weighted multigraph. Although the general problem is NP-complete, we identify polynomial time solvable special eases and derive good performance bounds for several natural approximation algorithms. The above results assume the existence of a central controller, but we also show how the approximation algorithms, along with their performance guarantees, can be adapted to a distributed regime.

Stochastic Network Model for Planning Scheduling

Abstract: A stochastic network model consisting of dependent and independent random variables is developed for construction scheduling. The network model is based on Monte‐Carlo simulation. Data for each network activity consist of a time distribution for the activity under optimal conditions and a series of time distributions for various problems that may lengthen the activity completion time. Dependencies between network activities may be modelled; also, time dependencies for a network activity may be modelled. The implementation of the model is discussed.

An Interactive Approach for Project Selection

Abstract: This paper describes an interactive method for presenting a sequence of feasible sets of indivisible projects to a decision-maker. For each set as a whole, the decision-maker evaluates its utilities with respect to each of several attributes; the utilities are then combined to give a single utility for the set. A sequence of zero-one programmes is used to ensure that the only sets presented are those which are feasible and which are not contained in larger feasible sets. The sets are presented in descending order of size, and the presentation can be terminated by the decision-maker or by supplementary rules. The method for presenting sets can be used in other contexts in which complete enumeration of possible sets would otherwise be required.

Optimal Parallel Scheduling of Gaussian Elimination DAG's

Abstract: A parallel algorithm for Gaussian elimination (GE) is described, which solves a linear system of size n using m ≤ n parallel processors and a shared random access memory. Converting the serial GE algorithm to parallel form involves scheduling its computation DAG (directed acyclic graph) on m processors. A lower bound for schedule length is established for dense GE DAG's and it is proved that the proposed algorithm produces schedules which achieve these bounds. Finally, both the construction and execution of the schedule are incorporated into a single concurrent program which is shown to run in optimal time.

Systematic design and programming of signal processors, using project management techniques

Abstract: This paper presents a systematic method of designing and microprogramming fast signal processors (SP's) while optimally utilizing the inherent parallelism of a given algorithm. The method employs graph-theoretical concepts and scheduling techniques from "project management" and permits an easy evaluation of the following key design parameters: i) the lower bound on the algorithm duration (T mp ) for given speeds of the arithmetic components in a signal processor, ii) the minimum arithmetic hardware requirements necessary for the completion of the algorithm within the time T mp , and iii) the optimum algorithm schedule and the corresponding minimum attainable duration T at , when constraints on the available SP resources are imposed. In combination with the data-flow analysis and resource allocation, the scheduling procedure permits the influence of the SP architecture on the schedule to be modeled and the basic architectural features of the SP to be determined. The results also provide information for automatic microprogram generation and for the assessment and comparison of signal processor performance and algorithm speeds. The synthesis of architectures is based on an "ideal, data-flow driven signal processor" that is introduced in the paper. The proposed design approach is demonstrated on various digital-filter algorithms.

Analysis of a Local-Area Bus System with Controlled Access

Abstract: The performance analysis of a local-area bus access scheme is presented, which is characterized by an alternating sequence of scheduling and data-transmission intervals. For different scheduling disciplines, viz., fixed and variable priorities, and "shortest-packet-first," we derive explicit results for the mean packet-transfer delay. Our results give insight into the question of fairness among the stations, and the potential for performance improvement by sophisticated scheduling.

A Statistical Study of the Performance of a Task Scheduling Algorithm

Abstract: In this note we report the results of an experimental investigation on the performance of the very simple level scheduling algorithm for unit time task systems. Although the problem of the construction of optimal k-processor schedules for unit time tasks is NP-complete, the experimental study suggests that this efficient linear time algorithm can produce optimal schedules most of the time in the sense that the probability of producing an optimal schedule using this efficient linear time algorithm is at least 0.9 for over 700 cases randomly constructed in our experiment.

The Use of Straight Line Distances in Solutions to the Vehicle Scheduling Problem

Abstract: This paper is concerned with the use of straight-line distances in algorithms concerned with the solution of the vehicle scheduling problem (V.S.P.). An empirical test is carried out to see whether transport operating cost between two points can be estimated from the corresponding straight-line distance, as often assumed in V.S.P. algorithms which have a cost-minimising objective. The use of variance in V.S.P. algorithms is also discussed, especially in relation to travelled times on links and limits on goods vehicle drivers' hours.