Wolfgang Slany

Scheduling as a fuzzy multiple criteria optimization problem

Abstract Real-world scheduling is decision making under vague constraints of different importance, often using uncertain data, where compromises between antagonistic criteria are allowed. The author explains in theory and by detailed examples a new combination of fuzzy set based constraints and iterative improvement repair based heuristics that help to model these scheduling problems. The mathematics needed for a method of eliciting the criterias importances from human experts are simplified. The author introduces a new consistency test for configuration changes. This test also helps to evaluate the sensitivity to configuration changes. The implementation of these concepts in the fuzzy logic inference processor library FLIP++, in the fuzzy constraint library ConFLIP++, in the dynamic constraint generation library DynaFLIP++, and in the heuristic repair library Deja Vu is described. All these libraries are implemented in a layered framework enhanced by the common user interface InterFLIP++. The benchmark application to compare the fuzzy constraint iterative improvement repair heuristic with constructive method based on classic constraints is a scheduling system for a continuous caster unit in a steel plant.

Current State of Agile User-Centered Design: A Survey

Agile software development methods are quite popular nowadays and are being adopted at an increasing rate in the industry every year. However, these methods are still lacking usability awareness in their development lifecycle, and the integration of usability/User-Centered Design (UCD) into agile methods is not adequately addressed. This paper presents the preliminary results of a recently conducted online survey regarding the current state of the integration of agile methods and usability/UCD. A world wide response of 92 practitioners was received. The results show that the majority of practitioners perceive that the integration of agile methods with usability/UCD has added value to their adopted processes and to their teams; has resulted in the improvement of usability and quality of the product developed; and has increased the satisfaction of the end-users of the product developed. The top most used HCI techniques are low-fidelity prototyping, conceptual designs, observational studies of users, usability expert evaluations, field studies, personas, rapid iterative testing, and laboratory usability testing.

Efficient generation of rotating workforce schedules

Generating high-quality schedules for a rotating workforce is a critical task in all situations where a certain staffing level must be guaranteed, such as in industrial plants or police departments. Results from ergonomics (BEST, Guidelines for shiftworkers, Bulletin of European Time Studies No. 3, European Foundation for the Improvement of Living and Working Conditions, 1991) indicate that rotating workforce schedules have a profound impact on the health and satisfaction of employees as well as on their performance at work. Moreover, rotating workforce schedules must satisfy legal requirements and should also meet the objectives of the employing organization. In this paper, our description of a solution to this problem is being stated. One of the basic design decisions was to aim at high-quality schedules for realistically sized problems obtained rather quickly, while maintaining human control. The interaction between the decision-maker and the algorithm therefore consists of four steps: (1) choosing a set of lengths of work blocks (a work block is a sequence of consecutive days of work), (2) choosing a particular sequence of blocks of work and days-off blocks amongst these that have optimal weekend characteristics, (3) enumerating possible shift sequences for the chosen work blocks subject to shift change constraints and bounds on sequences of shifts, and (4) assignment of shift sequences to work blocks while fulfilling the staffing requirements. The combination of constraint satisfaction and problem-oriented intelligent backtracking algorithms in each of the four steps allows for finding good solutions for real-world problems in acceptable time. Computational results from a benchmark example found in the literature confirmed the viability of our approach. The algorithms have been implemented in commercial shift scheduling software.

Local search for shift design

Abstract Designing shifts is one of the important stages in the general workforce scheduling process. In this paper we consider solving the shift design problem by using local search methods. First we propose a set of move types that give rise to a composite neighbourhood relation. In the move selection process, we make use of the basic prohibition mechanisms of tabu search. In addition, in order to avoid having to explore the whole neighbourhood which could be prohibitively large, we evaluate the moves in decreasing order of their promise to yield some improvement. Furthermore, we propose an algorithm for generating a good initial solution, which also exploits knowledge about requirements and shift structure. Experimental results on both real-life and randomly-generated instances show the advantages of these ingredients. The solver is part of a commercial product and has shown to work well in practical cases.

Comparison of iterative improvement techniques for schedule optimization

Abstract Due to complexity reasons of realistic scheduling applications, often iterative improvement techniques that perform a kind of local search to improve a given schedule are proposed instead of enumeration techniques that guarantee optimal solutions. In this paper we describe an experimental comparison of four iterative improvement techniques for schedule optimization that differ in the local search methodology. These techniques are iterative deepening, random search, tabu search and genetic algorithms. To compare the performance of these techniques, we use the same evaluation function, knowledge representation and data from one application. The evaluation function is defined on the gradual satisfaction of explicitly represented domain constraints and optimization functions. The satisfactions of individual constraints are weighted and aggregated for the whole schedule. We have applied these techniques on data of a steel making plant in Linz (Austria). In contrast to other applications of iterative improvement techniques reported in the literature, our application is constrained by a greater variety of antagonistic criteria that are partly contradictory.

On network design problems: fixed cost flows and the covering steiner problem

Network design problems, such as generalizations of the Steiner Tree Problem, can be cast as edge-cost-flow problems. An edge-cost flow problem is a min-cost flow problem in which the cost of the flow equals the sum of the costs of the edges carrying positive flow.We prove a hardness result for the Minimum Edge Cost Flow Problem (MECF). Using the one-round two-prover scenario, we prove that MECF does not admit a 2log1-ϵ n-ratio approximation, for every constant ϵ > 0, unless NP ⊆ DTIME(npolylogn).A restricted version of MECF, called Infinite Capacity MECF (ICF), is defined. The ICF problem is defined as follows: (i) all edges have infinite capacity, (ii) there are multiple sources and sinks, where flow can be delivered from every source to every sink, (iii) each source and sink has a supply amount and demand amount, respectively, and (iv) the required total flow is given as part of the input. The goal is to find a minimum edge-cost flow that meets the required total flow while obeying the demands of the sinks and the supplies of the sources. This problem naturally arises in practical scheduling applications, and is equivalent to the special case of single source MECF, with all edges not touching the source or the sink having infinite capacity.The directed ICF generalizes the Covering Steiner Problem in directed and undirected graphs. The undirected version of ICF generalizes several network design problems, such as: Steiner Tree Problem, k-MST, Point-to-point Connection Problem, and the generalized Steiner Tree Problem.An O(log x)-approximation algorithm for undirected ICF is presented. We also present a bi-criteria approximation algorithm for directed ICF. The algorithm for directed ICF finds a flow that delivers half the required flow at a cost that is at most O(nϵ/ϵ4) times bigger than the cost of an optimal flow. The running time of the algorithm is O(x2/ϵ ċ n1+1/ϵ), where x denotes the required total flow.Randomized approximation algorithms for the Covering Steiner Problem in directed and undirected graphs are presented. The algorithms are based on a randomized reduction to a problem called 1/2-Group Steiner. In undirected graphs, the approximation ratio matches the approximation ratio of Konjevod et al. [2002]. However, our algorithm is much simpler. In directed graphs, the algorithm is the first nontrivial approximation algorithm for the Covering Steiner Problem. Deterministic algorithms are obtained by derandomization.

Making Apps Useable on Multiple Different Mobile Platforms: On Interoperability for Business Application Development on Smartphones

The relevance of enabling mobile access to business enterprise information systems for experts working in the field has grown significantly in the last years due to the increasing availability of smartphones; the shipment of smartphones exceeded that of personal computers in 2011. However, the screen sizes and display resolutions of different devices vary to a large degree, along with different aspect ratios and the complexity of mobile tasks. These obstacles are a major challenge for software developers, especially when they try to reach the largest possible audience and develop for multiple mobile platforms or device types. On the other side, the end users’ expectations regarding the usability of the applications are increasing. Consequently, for a successful mobile application the user interface needs to be well-designed, thus justifying research to overcome these obstacles. In this paper, we report on experiences during an industrial project on building user interfaces for database access to a business enterprise information system for professionals in the field. We discuss our systematic analysis of standards and conventions for design of user interfaces for various mobile platforms, as well as scaling methods operational on different physical screen sizes. The interoperability of different systems, including HTML5, Java and .NET is also within the focus of this work.

From extreme programming and usability engineering to extreme usability in software engineering education (XP+UE /spl rarr/ XU)

The success of extreme programming (XP) is based, among other things, on an optimal communication in teams of 6-12 persons, simplicity, frequent releases and a reaction to changing demands. Most of all, the customer is integrated into the development process, with constant feedback. This is very similar to usability engineering (UE) which follows a spiral four phase procedure model (analysis, draft, development, test) and a three step (paper mock-up, prototype, final product) production model. In comparison, these phases are extremely shortened in XP; also the ideal team size in UE user-centered development is 4-6 people, including the end-user. The two development approaches have different goals but, at the same time, employ similar methods to achieve them. It seems obvious that there must be synergy in combining them. The authors present ideas in how to combine them in an even more powerful development method called extreme usability (XU). The most important issue of this paper is that the authors have embedded their ideas into software engineering education.

User Interface Design for a Mobile Multimedia Application: An Iterative Approach

Mobile phones have become full-featured mobile computers. Applications providing good user experience and taking full advantage of the increasing capabilities of mobile phones are still rare. One such application is audio and video on mobile phones which is expected to become a killer application in the near future. A lot of valuable audio and video content is hidden in archives of content providers. We are developing an application that enables a user to perform content-based search for audio and video content in large databases and play it on a mobile phone virtually anywhere, at any time. Our approach to application development focuses on the adoption of agile software development methodologies and user-centered design, emphasizing iterative user-interface development involving usability engineers and non-technical users. Thus, the application evolves according to the needs of the end user, providing maximized usability and customer satisfaction.

ROS-based mapping, localization and autonomous navigation using a Pioneer 3-DX robot and their relevant issues

The Robot Operating System (ROS) provides operating system-like services to operate robots. Mapping, localization, and autonomous navigation in an indoor environment are popular issues in the field of autonomous robots. Autonomous navigation in a dynamic environment is not only challenging but also uncovers many indoor environmental factors which affect the process of mapping and navigation. The presented work describes how a ROS-based control system is used with a Pioneer 3-DX robot for indoor mapping, localization, and autonomous navigation. Mapping of different challenging environments is presented in this work. Moreover, some factors associated with indoor environments that can affect mapping, localization, and automatic navigation, are also presented. For experiments, three environments (one artificial and two real) have been tested. Some implementation was done in C and Python.