Handling Human-Centered Systems Uncertainty Using Fuzzy Logics – A Review <s> INTRODUCTION <s> Abstract The perspectives and potential impact of the concept of fuzziness in human factors studies are explored. It is advocated that fuzzy methodologies should be applied in this field of research to a much greater extent than has been done in the past. <s> BIB001 </s> Handling Human-Centered Systems Uncertainty Using Fuzzy Logics – A Review <s> INTRODUCTION <s> As its name suggests, computing with words (CW) is a methodology in which words are used in place of numbers for computing and reasoning. The point of this note is that fuzzy logic plays a pivotal role in CW and vice-versa. Thus, as an approximation, fuzzy logic may be equated to CW. There are two major imperatives for computing with words. First, computing with words is a necessity when the available information is too imprecise to justify the use of numbers, and second, when there is a tolerance for imprecision which can be exploited to achieve tractability, robustness, low solution cost, and better rapport with reality. Exploitation of the tolerance for imprecision is an issue of central importance in CW. In CW, a word is viewed as a label of a granule; that is, a fuzzy set of points drawn together by similarity, with the fuzzy set playing the role of a fuzzy constraint on a variable. The premises are assumed to be expressed as propositions in a natural language. In coming years, computing with words is likely to evolve into a basic methodology in its own right with wide-ranging ramifications on both basic and applied levels. <s> BIB002
Human-Centered Systems (HCS) is understood as the system Human-Machine-Environment, i.e., the people at work and their relations with the surrounding environment, equipment and fellow workers. The analysis of such systems can be performed aiming different goals -like safety, health, human reliability, stress or usability-, and may be addressed from different perspectives -like the physical, physiological, organizational, cognitive, or socio-psychological. A HCS intervention can be performed at a design or redesign phase of a work system, and is focused on identifying incompatibilities between work requirements and hazards, and human capabilities. The objective is eliminating the incompatibilities or, at least, reducing them, so that working systems become safer, healthier, more productive, comfortable, and satisfying BIB001 . Is a basic principle in the law of many countries that employers have to take the necessary measures for the safety and health protection of workers. For instance, within the European Community, the legal framework was settled by the Council Directive of 12 June 1989 on the introduction of measures to encourage improvements in the safety and health of workers at work (89/391/EEC), and then adopted by Member States' national laws. For this purpose employers must analyze HCS regarding safety and health at work, and decide on preventive measures to take and, if necessary, protective equipment to use. The knowledge required to analyze HCS is multidisciplinary and the data used to evaluate them is often characterized by being complex, imprecise, uncertain and vague. The problem complexity and data vagueness (for *Address correspondence to this author at the Universidade Nova de Lisboa/ Faculdade de Ciências e Tecnologia, Departamento de Eng. Mecânica e Industrial, Campus de Caparica, 2829-516 Caparica, Portugal; Tel: +351 21 294 85 42; Fax: +351 21 294 85 46; E-mail: imn@fct.unl.pt instance, the ill-definition resulting from the subjective nature of human classifications) renders classical logics approaches almost useless to deal with HCS. Fuzzy Logics (FL) provides an appropriate logicalmathematical framework to handle problems with such characteristics, since BIB002 : • deals with uncertainty and imprecision of reasoning processes; • allows the modeling of the heuristic knowledge (that cannot be described by traditional mathematical equations); and • allows the computation of linguistic information. The aim of this paper is to divulge examples of the application of FL in HCS highlighting the advantages that arise from the use of the fuzzy methodology. This paper presents a survey on the publications issued on the last 12 years regarding the use of fuzzy logic in human-centered systems. The sources were Portuguese and English language edited books and papers retrieved from searches in databases such as B-on, ISI Web of knowledge and INSPEC, using expressions such as: "FL and Ergonomics", "FL and Safety" or "FL and occupational stress". The following sections of paper will provide a brief overview about Fuzzy Logics, present several examples of fuzzy systems applied in the assessment of HCS-related issues, namely, comfort, human reliability, workload stress, health, and safety. At the end some conclusions will also be presented.