J. Steve Davis

Single-machine scheduling with early and tardy completion costs

We address a single-machine scheduling problem in which penalties are assigned for early and tardy completion of jobs. These penalties are common in industrial settings where early job completion can cause the cash commitment to resources in a time frame earlier than needed, giving rise to early completion penalties. Tardiness penalties arise from a variety of sources, such as loss of customer goodwill, opportunity costs of lost sales, and direct cash penalties. Accounting for earliness cost makes the performance measure nonregular, and this nonregularity has apparently discouraged researchers from seeking solutions to this problem. We found that it is not much more difficult to design an enumerative search for this problem than it would be if the performance measure were regular. We present and demonstrate an efficient timetabling procedure which can be embedded in an enumerative algorithm allowing the search to be conducted over the domain of job permutations.© 1993 John Wiley & Sons, Inc.

Tools for spreadsheet auditing

Few tools are available for understanding and debugging spreadsheets, but they are needed because spreadsheets are being used for large, important business applications. The key to understanding spreadsheets is to clarify the data dependencies among cells. We developed and evaluated two interactive tools which aid in investigating data dependencies, an on-line flowchart-like diagram and a tool which represents dependencies by drawing arrows among cells on the display of the spreadsheet. Users found both tools helpful, but preferred the arrow tool.

Automatic measurement extraction for apparel from a three-dimensional body scan

This paper describes a project involving computer assisted measurement extraction from a three-dimensional (3D) noncontact fullbody scan. It explains the motivation behind the project, describes briefly the research plan and provides details on the measurement extraction software currently being developed. The software provides the user with tools to take measurements from a digitized image. In addition, a measurement extraction language allows the user to develop macros, or short programs, designed to automate the measurement extraction process. The paper concludes with a description of the current status of the project.

A simple heuristic for maximizing service of carousel storage

Abstract We consider a system that stores cases of items. Items are removed from storage in groups. A group consists of a certain number of items of each type. The (integer maximization) problem is to determine how many cases of each type should be stored in order to maximize the number of groups of items that can be retrieved without re-loading. We give a simple heuristic that yields a feasible solution whose error can be bounded. Our method takes only linear time. Scope and purpose Performance of an automated storage and retrieval system such as a carousel depends greatly upon the way it is loaded. Commonly a carousel will be loaded with cases of items that will be retrieved in groups. A group is a certain number of items of each type. For example, a group might constitute the parts needed to manufacture one instance of a product. Typically the carousel operator wants to retrieve as many groups as possible without running out of items of any type. We present a simple heuristic that prescribes how many cases of each item type should be loaded. The number of groups supplied by our solution is close to optimal. The solution is given by explicit equations, and can be computed in time linear in the number of item types.

Factors affecting decision support system benefits

Abstract Almost every DSS researcher has identified evaluation of DSS as an important research direction. Most previous studies of DSS benefits have failed to address the intangible benefits. This study investigated the relationship of selected predictor variables with the tangible and intangible benefits of DSS utilization in the financial services industry. A mail survey involving 121 DSS users from this industry was used to examine benefits of DSS and the factors determining them. Results indicated that benefits are affected by four groups of factors: Industry, organization, system, and user attributes.

Schedule instability, service level and cost in a material requirements planning system

The primary objective of this work was to evaluate how four important system parameters (schedule frozen interval, schedule re-planning interval, safety stock and lot-sizing rules) affect material requirements planning (MRP) system performance in terms of schedule instability, total cost and service level, considering different levels of two operating factors: the lead-times of items in the product structure, and the accuracy of the demand forecast. The research design employed a simulation model in Visual Basic run on a personal computer. This study concluded that all system parameters and operating factors significantly influence the three performance measures. Frozen interval, forecast accuracy, and lead-time have the most significant impact on system instability and total cost. Forecast accuracy, safety stock, and lead-time have the most impact on service level. Due to the interactions among system parameters and operating factors, there are no win-win principles to set parameters in order to achieve better system performance under all operating conditions. However, the results help determine appropriate system parameters under particular operating conditions. For example, when the forecast is more accurate, system instability is relatively insensitive to the size of re-planning interval, but frequent re-planning helps reduce total cost and improve service level.

Production scheduling: an interactive graphical approach

Abstract This project developed an interactive computer graphics approach to construction and modification of schedules for a work center. The system handles problems involving sequence-dependent setup times for products of the work center and penalties for both early and late completion of jobs. A schedule of jobs is displayed as a Gantt chart. Jobs appear as color-coded bars whose lengths represent setup and processing times. If a job follows another of the same color, there is no setup time. The user can manually revise a schedule by “drag and drop” manipulation of the job icons and can invoke built-in routines to automatically reschedule. The system displays a number of quality measures and other schedule implications to aid the user in evaluating schedules.

A guessing measure of program comprehension

An effective comprehension measure could be helpful in ranking programs on complexity. Measures involving filling in missing parts of a program can be adapted from the prose domain. For example, cloze tests have been applied to software. We evaluated a new measure based on a fill-in-the-blank exercise conducted by an automated tool. The subject is asked to guess certain characters which are missing from a sample program which is displayed on a computer screen. The value of the measure is derived on an information-theoretic basis from the number of incorrect guesses. This measure has shown promise in experimental evaluations of its ability to measure program comprehension.

A Fast Algorithm for Shelf Optimization

Performance of an automated storage and retrieval system such as a carousel depends upon the way it is loaded. Commonly a carousel will be loaded with cases of items that will be removed in groups. A group is a specified number of items of each type. For example, a group might constitute the collection of parts needed to manufacture one garment. Typically the storage system operator wants to retrieve as many groups as possible without running out of items of any type. We present a fast algorithm that prescribes how many cases of each item type should be loaded, yielding a maximal number of groups.

Data dependency diagrams for spreadsheet applications

We conducted experiments to evaluate on-line data dependency diagrams for spreadsheets. Results were consistent those of earlier experiments with written data dependency diagrams. Although users had no trouble browsing the on-line diagrams, the diagrams did not seem to improve the performance of a maintenance task on a small spreadsheet. The diagrams may be helpful for larger spreadsheets.