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Showing papers on "Scheduling (computing) published in 1976"


Journal ArticleDOI
TL;DR: It is shown that significant reductions in crane travel time and distance are obtainable from turnover-based rules, and these improvements can be directly translated into increased throughput capacity for existing systems, and may be used to alter the design of proposed systems.
Abstract: In the past few years, increasing numbers of automatic warehousing systems using computer-controlled stacker cranes have been installed. Our research concerns the scientific scheduling and design of these systems. There are three elements to scheduling: the assignment of multiple items to the same pallet Pallet Assignment; the assignment of pallet loads to storage locations Storage Assignment; and rules for sequencing storage and retrieve requests Interleaving. This paper deals with optimal storage assignment. Results are obtained which compare the operating performance of three storage assignment rules: random assignment, which is similar to the closest-open-location rule used by many currently operating systems; full turnover-based assignment: and class-based turnover assignment. It is shown that significant reductions in crane travel time and distance are obtainable from turnover-based rules. These improvements can, under certain circumstances, be directly translated into increased throughput capacity for existing systems, and may be used to alter the design e.g., size and number of racks, speed of cranes, etc. of proposed systems in order to achieve a more desirable system balance between throughput and storage capacity.

606 citations


Journal ArticleDOI
TL;DR: Three general techniques are presented to obtain approximate solutions for optimization problems solvable in this way, and polynomial time algorithms are applied to obtain “good” approximate solutions.
Abstract: The following job sequencing problems are studied: (i) single processor job sequencing with deadlines, (ii) job sequencing on m-identical processors to minimize finish time and related problems, (iii) job sequencing on 2-identical processors to minimize weighted mean flow time. Dynamic programming type algorithms are presented to obtain optimal solutions to these problems, and three general techniques are presented to obtain approximate solutions for optimization problems solvable in this way. The techniques are applied to the problems above to obtain polynomial time algorithms that generate “good” approximate solutions.

561 citations


Journal ArticleDOI
TL;DR: Exact and approximate algorithms are presented for scheduling independent tasks in a multiprocessor environment in which the processors have different speeds and are guaranteed to obtain solutions that are close to the optimal.
Abstract: Exact and approximate algorithms are presented for scheduling independent tasks in a multiprocessor environment in which the processors have different speeds. Dynamic programming type algorithms are presented which minimize finish time and weighted mean flow time on two processors. The generalization to m processors is direct. These algorithms have a worst-case complexity which is exponential in the number of tasks. Therefore approximation algorithms of low polynomial complexity are also obtained for the above problems. These algorithms are guaranteed to obtain solutions that are close to the optimal. For the case of minimizing mean flow time on m-processors an algorithm is given whose complexity is O(n log mn).

452 citations


Journal ArticleDOI
TL;DR: A nurse scheduling system that poses the scheduling decision as a large multiple-choice programming problem whose objective function quantifies preferences of individual nursing personnel concerning length of work stretch, rotation patterns, and requests for days off is described.
Abstract: This paper describes a nurse scheduling system, the heart of which poses the scheduling decision as a large multiple-choice programming problem whose objective function quantifies preferences of individual nursing personnel concerning length of work stretch, rotation patterns, and requests for days off. The constraints provide for minimum numbers of nursing personnel of each skill class to be assigned to each day and shift of a four-or six-week scheduling period. The problem is solved by a modification of Balintfy and Blackburn's algorithm for multiple-choice programming problems. We include a description of the implementation of the scheduling system on nursing units of several hospitals.

285 citations


Journal ArticleDOI
TL;DR: This paper describes an integer programming formulation of the vehicle scheduling problem and illustrates how such a formulation can be extended to incorporate restrictions on work load, coverage and service that occur in real world vehicle scheduling problems.
Abstract: This paper describes an integer programming formulation of the vehicle scheduling problem and illustrates how such a formulation can be extended to incorporate restrictions on work load, coverage and service that occur in real world vehicle scheduling problems. The integer programme is solved using the Revised Simplex method, additional constraints being introduced to retain integrality during convergence. The feasible region of this integer programme is initially restricted so that only routes constructed through sets of radially contiguous locations are considered. The effect of relaxing these over-constraints is explored. The method is demonstrated on fifteen problems ranging in size from 21 to 100 locations and the results generally show an improvement on previously published results. This is particularly true of the larger problems. This method compares favourably with other methods in computational efficiency.

231 citations


Journal ArticleDOI
TL;DR: This paper considers the project scheduling problem with multiple constrained resources and shows that the choice of priority rule is important with the parallel method, but with the sampling method, although it does affect the distribution of the sample, the choices of rule are not significant.
Abstract: This paper considers the project scheduling problem with multiple constrained resources. Two classes of heuristic procedure, both making use of priority rules, are discussed: the parallel method, which generates just one schedule; and the sampling method, which generates a set of schedules using probabilistic techniques and selects the best schedule from this sample. An experimental investigation is described in which a set of projects with different characteristics is scheduled by each of these heuristics with a variety of priority rules. The effects of the heuristic method, the project characteristics and the priority rules are assessed. It is shown that the choice of priority rule is important with the parallel method, but with the sampling method, although it does affect the distribution of the sample, the choice of rule is not significant. The sampling method with sample size 100 is shown to produce samples at least 7% better than those generated by the corresponding parallel method, with 99% confidence. Further results are discussed and conclusions are presented.

180 citations


Patent
19 Jan 1976
TL;DR: In this paper, the scheduling of output traffic to ports is handled by individual processors on an exclusive assignment basis, when a port is available to handle a given traffic segment (packet) destined for that port signals such availability to the processor having current responsibility over the transfer of said segment. The latter processor then executes the operations required to complete the transfer.
Abstract: Apparatus and method for carrying out data switching; e.g. at a store-and-forward exchange node in a data communication network. Plural processors operate relative to multiple ports and traffic storage queues, partially on an exclusive basis and partially on a shared basis, to effectuate switching of data traffic with balanced sharing of the aggregate processing load. The processors control traffic processing functions (reception, storage and output transfer) on a varied assignment schedule. Supervisory signals exchanged between processors indicate status and destinations of currently stored traffic loads. The scheduling of output traffic to ports is handled by individual processors on an exclusive assignment basis. When a port is available to handle a given traffic segment (packet) destined for that port the respective processor having exclusive output scheduling responsibility for that port signals such availability to the processor having current responsibility over the transfer of said segment. The latter processor then executes the operations required to complete the transfer.

129 citations


Journal ArticleDOI
TL;DR: Heuristic methods are presented for scheduling telephone traffic exchange operators to meet demand that varies over a 24-hour operating period, both in terms of solution quality and computational efficiency.
Abstract: Heuristic methods are presented for scheduling telephone traffic exchange operators to meet demand that varies over a 24-hour operating period. Two types of heuristics are described 1 for determining the work shift types to be considered in preparing an operator shift schedule and 2 for constructing an operator shift schedule from a given set of work shift types. These heuristics are evaluated both in terms of solution quality and computational efficiency, using actual operating data.

128 citations


Journal ArticleDOI
01 Aug 1976
TL;DR: An experimental method of scheduling the necessary maintenance activities on generator units in a power system based on the branch-and-bound technique, which results in a practically implementable solution, if a feasible solution exists.
Abstract: An experimental method of scheduling the necessary maintenance activities on generator units in a power system is developed. The problem is identified as an integer programming problem, and a method based on the branch-and-bound technique is developed. The maintenance scheduling problem is characterized by a large number of complex constraints. The method presented is capable of taking into account all these constraints and hence, results in a practically implementable solution, if a feasible solution exists. Other features of the method are employment of a number of different objective functions and discovery of a feasible solution if one exists. Furthermore, unlike most present methods, it actually finds the optimal solution. The operation of the method is exemplified by application to a realistic system.

109 citations


Journal ArticleDOI
TL;DR: In this article, the problem of scheduling jobs on a single machine subject to given release dates and precedence constraints, in order to minimize maximum lateness, was considered and the algorithms of Baker and Su (Naval Res. Quart. 21 (1974) 171-176) and of McMahon and Florian (Operations Res. 23 (1975) 475-482) for the problem without precedence constraints were extended to the general case.
Abstract: Summary We consider the problem of scheduling jobs on a single machine subject to given release dates and precedence constraints, in order to minimize maximum lateness. The algorithms of Baker and Su (Naval Res. Logist. Quart. 21 (1974) 171–176) and of McMahon and Florian (Operations Res. 23 (1975) 475–482) for the problem without precedence constraints are extended to the general case. An extensive computational comparison establishes the superiority of the latter algorithm. We describe applications to the theory of job-shop scheduling and to a practical scheduling situation.

103 citations



Journal ArticleDOI
TL;DR: The basic principles enabling one to define essential characteristics of the feasible solutions for a job-shop scheduling problem in which the jobs are constrained by fixed starting times and due dates are presented.
Abstract: This note is concerned with some essential characteristics of the feasible solutions for a job-shop scheduling problem in which the jobs are constrained by fixed starting times and due dates. These characteristics are related to the scheduling order of operations on each machine and to the fixed starting and completion times for each operation. We present the basic principles enabling one to define these characteristics and propose a procedure for finding them.

Journal ArticleDOI
TL;DR: A model for disk accesses based on published measurements is developed and is used to show that under highly probable conditions, FCFS seek scheduling is superior to SSTF scheduling in the sense of having a lower mean queue length.
Abstract: A model for disk accesses based on published measurements is developed. The model is used to show that under highly probable conditions, FCFS seek scheduling is superior to SSTF scheduling in the sense of having a lower mean queue length. A simple example of an arrival sequence illustrating this anomaly is presented.

Journal ArticleDOI
TL;DR: An algorithm is introduced where the role of the heuristic scheduling urgency factor is expanded from one of solely determining the order in which activities are considered for scheduling at a given instant, to one of determining the combination of activities to be scheduled at this instant.
Abstract: This paper extends the field of heuristic algorithms for resource constrained scheduling problems in three important areas. First, an algorithm is introduced where the role of the heuristic scheduling urgency factor is expanded from one of solely determining the order in which activities are considered for scheduling at a given instant, to one of determining the combination of activities to be scheduled at this instant. Second, a new hybrid scheduling urgency factor capitalizing on the fact that this algorithm is sensitive to the absolute value rather than relative sequence of the urgency factors is introduced. Finally, a systematic approach to the evaluation of such algorithms is introduced. This includes the identification of relevant problem attributes and the adoption of evaluative concepts such as computational efficiency and analytic and systems effectiveness.

Journal ArticleDOI
TL;DR: A new algorithm is given that converges to a local optimum for both problems and is shown to be incorrect and a counter example is presented.
Abstract: A result of Smith previously published in this journal [3], on the use of secondary criteria in scheduling problems, is shown to be incorrect and a counter example is presented. Heck and Roberts [2] suggested that their paper would be extended in the same way Smith's algorithm was. A new algorithm is given that converges to a local optimum for both problems.

Journal ArticleDOI
TL;DR: Investigating aspects of this evolutionary extension of the operating system called the dynamically adaptive operating system (DAOS) include the general methodology and the real-time modeling and estimation of resource demands and a dynamically partitioned second moment model is described.
Abstract: -Real-time optimization of the overall performance of a large computer system or network such as an air-traffic control system or teleprocessing network inherently requires the introduction of adaptive control into selected control functions or sets of control functions. Such adaptive control is necessitated by the high variance of the available resource inventory and the workload resource demands within the system environment. Global management of the resulting multiloop control system becomes the responsibility of the operating system. Investigated aspects of this evolutionary extension of the operating system called the dynamically adaptive operating system (DAOS) include the general methodology and the real-time modeling and estimation of resource demands. The methodology specifies the general identification, decision, and modification processes required for an adaptive operating system. Support of such processes could be attractively provided by a peripheral or miniprocessor. The problem of estimating resource service times both with and without partial service times is explored and statistical models possessing utility for real-time modeling are developed. In particular, a dynamically partitioned second moment model (DPSMM) is described. The feasibility of such models is established with respect to a General Principle of Locality. Selected simulation results are presented to evaluate selected developments with respect to an adaptive central processing unit (CPU) scheduling discipline.

Journal ArticleDOI
TL;DR: An extension of previous work is developed and an algorithm is presented for the classical vehicle scheduling problem where a set of vehicles with known capacities are to service a known set of points with deterministic demands at least cost.
Abstract: This paper is concerned with the classical vehicle scheduling problem where a set of vehicles with known capacities are to service a known set of points with deterministic demands at least cost. An extension of previous work is developed and an algorithm is presented. Suitable computational experience with the procedure is provided for both the symmetric and the non-symmetric problems.

Journal ArticleDOI
TL;DR: A method of scheduling machines is presented which incorporates the facility of providing proven optimum solutions for minimum throughput time, and includes a new, job based, bounding procedure which is well suited to the situation where all jobs are not processed by all machines.
Abstract: A method of scheduling machines is presented which incorporates the facility of providing proven optimum solutions for minimum throughput time. The method employs branch and bound procedures and includes a new, job based, bounding procedure which is well suited to the situation where all jobs are not processed by all machines. Comparisons are made with well known bounding procedures and computational experience is reported with examples taken from real applications.

Journal ArticleDOI
TL;DR: One of the primary functions of an operating system is to distribute the resources under its control among the users of the system in such a way as to achieve installation standards of performance (including service).
Abstract: One of the primary functions of an operating system is to distribute the resources under its control among the users of the system in such a way as to achieve installation standards of performance (including service).

Journal ArticleDOI
TL;DR: In this article, the problem of non-preemptive scheduling of a set of independent periodic jobs in a computer system characterized by a collection of processors, memories, and interconnection mechanisms is investigated.
Abstract: This investigation considers the problem of the nonpreemptive scheduling of a set of independent periodic jobs in a computer system characterized by a collection of processors, memories, and interconnection mechanisms. Such a collection of resources can be used to perform the functions of a process control environment as are found, for example, in the avionics of a military or commercial aircraft. The distribution of these resources permits weight, volume, power, cost, and reliability requirements to be satisfied. Each periodic job is characterized by its frequency and its execution time. The inverse of the frequency, the period, is assumed to be an integer, and the initiation time and the completion time of job must be strictly met. An optimal algorithm is developed for a job set whose members are related by a binary frequency distribution. That is, if the jobs in the set are ordered in terms of decreasing job execution frequency, then fi = 2fi+1. The optimal result is generalized to include conditions in which the jobs are related by fi = kfi+1, where k is an integer.


Journal ArticleDOI
TL;DR: A queuing model incorporating the processor scheduling algorithm for IMS (Information Management System) is formulated in order to illustrate the modeling ideas and should be viewed as illustrative of stochastic models which can be constructed to incorporate algorithms for processor scheduling.
Abstract: This paper is concerned with the stochastic modeling of processor scheduling and of queuing due to contention for resources in data base management systems. The processing services rendered in searching the data base and retrieving and processing information are modeled explicitly, as is the algorithm used to schedule these services on the processor. The scheduling of the processor is based on a total priority ordering of a set of queues for processing service. A queuing model incorporating the processor scheduling algorithm for IMS (Information Management System) is formulated in order to illustrate the modeling ideas. The model is analyzed under rather general distributional assumptions, based on the observation that certain stochastic processes in the model are cumulative processes defined over the same embedded semi-Markov process. The model is not used in a performance study of IMS, nor is it proposed that the model developed here is one upon which a performance study of IMS should be undertaken. The model should be viewed as illustrative of stochastic models which can be constructed to incorporate algorithms for processor scheduling.

Journal ArticleDOI
TL;DR: This paper applies the technique of systematic programming for programming scheduling algorithms as encountered in operating system design to illustrate the usefulness of the monitor concepts and the synchronizing method.
Abstract: This paper applies the technique of systematic (or structured) programming for programming scheduling algorithms as encountered in operating system design. Monitors are used for structuring scheduling algorithms and a synchronizing method is proposed for process scheduling. Some fairly difficult scheduling problems are solved systematically to illustrate the usefulness of the monitor concepts and the synchronizing method. Certain implementation aspects are also discussed.

Journal ArticleDOI
TL;DR: The daily scheduling problem is discussed in terms of scheduling with and without simultaneous work assignment; and the weekly problem is dichotomized into those schedules based on cyclical personnel requirements and those that are not.
Abstract: In many public systems efficiencies may be realized by improved personnel scheduling. This paper surveys the literature on personnel scheduling in the public domain. Two general problems are considered: the daily scheduling problem where hourly employee work day patterns are determined and the weekly scheduling problem where day off and day on work week patterns are constructed. The daily problem is discussed in terms of scheduling with and without simultaneous work assignment; and the weekly problem is dichotomized into those schedules based on cyclical personnel requirements and those that are not.

01 Jan 1976
TL;DR: In this article, a detailed computer system was used to schedule a fleet of only five ships, which allowed each ship to be assigned to additional jobs for one day per month, relative to the number of ships scheduled.
Abstract: Advanced benefits in the pool result can be achieved by applying modern scheduling techniques, in conjunction with electronical data processing. Even with a fleet of only five ships, the detailed computer system proved to be superior to manual techniques of experienced schedulers. The computed schedule permitted, on the average, each ship to be assigned to additional jobs for one day per month. This effect increases relative to the number of ships scheduled. For an EDP-system to be effective it is necessary to use the basic information concerning the scheduling; including information on short term alterations, such as subletting or offers on the free market. The analysis of changes within the scheduling system normally involves a great manual effort. To overcome this problem the scheduler is able to communicate on line, in dialogue with the computer through the console, direct from his workplace. Depending upon the required information and the urgency of the reply, the scheduler is able to select, at distinct levels, an analysis of the effect of a particular operation. At the first stage, he obtains the variations of the economic pool result by changes and decisions relative to the schedule. At the next level, notice of the best possibilities of voyage combinations and assignments for ships and contracts are given. In the last stage, the system computes the schedule with the best pool result.

Proceedings ArticleDOI
29 Mar 1976
TL;DR: A class of schedules in the two customer central server queueing model, consisting of a “CPU” server and m “I/O” servers, is considered and optimal (maximal CPU utilization) CPU and I/O schedules are obtained.
Abstract: A class of schedules in the two customer central server queueing model, consisting of a “CPU” server and m “I/O” servers, is considered. Optimal (maximal CPU utilization) CPU and I/O schedules are obtained. The best CPU schedule depends on the I/O schedule in effect; and is either Longest or Shortest-Expected-Remaining-Processing-Time-First. However, for certain I/O schedules the CPU schedule is immaterial. The best I/O schedule is always to process the (expected) longer CPU customer first.

Proceedings Article
01 Jan 1976
TL;DR: In this article, the authors describe software techniques developed for the Unified Data System (UDS), a distributed processor network for control and data handling onboard a planetary spacecraft, including a structured language for specifying the programs contained in each module.
Abstract: The paper describes software techniques developed for the Unified Data System (UDS), a distributed processor network for control and data handling onboard a planetary spacecraft. These techniques include a structured language for specifying the programs contained in each module, and a small executive program in each module which performs scheduling and implements the module task.

Journal ArticleDOI
01 Jul 1976
TL;DR: A methodology is developed through simulation which reduces supervisor queueing by scheduling jobs to processors such that they request the use of the supervisor when the supervisor is predicted to be available.
Abstract: In a multiprocessor system, the handling of interrupts generated by jobs in the processors is assigned to a supervisory program and associated data base The two basic philosophies for deciding which processor executes the supervisor are master-slave and floating executive control In either case, queueing of requests to the supervisor may occur With the master-slave structure, the master processor can handle only one request at a time With floating executive control, while any processor can execute the supervisor, only one processor at a time can be allowed to access the supervisor's data baseA processor which is waiting to use the supervisor is not doing useful work Therefore, queueing of requests to the supervisor causes a degradation in the performance of the system Previous studies have indicated that this degradation is significant for systems with a large number of processorsA methodology is developed through simulation which reduces supervisor queueing by scheduling jobs to processors such that they request the use of the supervisor when the supervisor is predicted to be available Information concerning job execution characteristics required by the scheduler is shown to be available at sufficient accuracy via dynamic monitoring and forecasting during normal program execution

Book
01 Jan 1976
TL;DR: A methodology for inserting fixed delays in a pipeline to achieve desired collision characteristics is presented and the objective is to have the throughput, i.e., average number of tasks processed per unit time, be maximized while providing considerable flexibility in scheduling of tasks.
Abstract: : A pipeline as defined here is a collection of segments of hardware which can operate simultaneously. A task flows synchronously from segment to segment for its execution. Each task follows one of several distinct task flow patterns which are assumed to be fixed and known in advance. It is characteristic of pipelines that a task can be initiated in the pipeline before an earlier initiated task has completed its execution. A problem arises when two or more tasks try to use the same segment at the same time, causing a collision. Such collisions can be avoided by appropriate scheduling of tasks and/or modification of the pipeline; or the collisions can be resolved at the time and place they occur. These alternatives are studied in this work with the objective that the throughput, i.e., average number of tasks processed per unit time, be maximized while providing considerable flexibility in scheduling of tasks. Collision characteristics of task schedules and pipelines are studied. A methodology for inserting fixed delays in a pipeline to achieve desired collision characteristics is presented.

Journal ArticleDOI
TL;DR: Analysis of a transformation of the original graph into another graph, whose precedences do not violate the optimality constraints and has a unique basic schedule provides insight into the scheduling process and also into the determination of lower bounds on the number of processors and on time.
Abstract: The scheduling of a set of tasks, with precedence constraints and known execution times, into a set of identical processors is considered. Optimal scheduling of these tasks implies utilizing a minimum number of processors to satisfy a deadline, or finishing in minimal time using a fixed number of processors. This process can be seen as a transformation of the original graph into another graph, whose precedences do not violate the optimality constraints and has a unique basic schedule. Analysis of this transformation provides insight into the scheduling process and also into the determination of lower bounds on the number of processors and on time for optimal schedules.