Abstract. Along tasks analysis and modeling history it has been demonstrated by experience that task modeling activities become cumbersome when performed on large, real-life systems. However, one of the main goals of task models is to provide designers with a structured and complete description of the users tasks especially when these user tasks are numerous and/or complex. Several authors proposed to handle that problem by providing tools aiming at supporting both construction and understanding (usually via simulation) of models. One of the most popular examples is CTTE environment which is dedicated to the engineering of CTT task models. The paper shows how to extend notations for task description with two kinds of mechanisms: composition and refinement/abstraction. Refinement/abstraction mechanisms make it possible to decompose a task model into several models and to interconnect them. Composition mechanisms make it possible to define communication means between task models. The paper proposes a precise definition of these mechanisms, their integration into a notation for describing task models and demonstrates that altogether, these two structuring mechanisms support the effective exploitation of task models for large scale application. The use of the mechanisms is presented on a real-life case study from the space domain describing operators' tasks to monitor a satellite and manage failures.

Task analysis can be considered as a fundamental component of user centered design methods as it provides a unique way of analyzing in a systematic way users' roles and activities. A widely used way of storing the information gathered during that phase in a structured and exhaustive way is to build task models which are then amenable to verification of properties or to performance evaluation. In widely used notations such as Hierarchical Task Analysis (HTA) or CTT (Concur Task Tree), information or objects manipulated by the users while performing the tasks does not receive a similar treatment as the sequencing of tasks which is usually carefully and exhaustively described. This paper proposes a systematic account for the various concepts manipulated by the users while performing tasks. Such concepts include different types of knowledge (declarative, situational, procedural and strategic), objects (manipulated by the user) and information. These concepts are systematically represented in a set of extensions of the HAMSTERS notation allowing the analysis of concepts-related properties such as learning curve, complexity, information workload, … We demonstrate the application of the approach on the example of a two players game making explicit the connection between these extended task models and the user interface of the game.

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 15322The contribution was presented at INTERACT 2015 : http://www.interact2015.org/ Any correspondence concerning this service should be sent to the repository administrator: staff-oatao@listes-diff.inp-toulouse.fr Enhanced Task Modelling for Systematic Identification and Explicit Representation of Human ErrorsRacim Fahssi, Célia Martinie, Philippe Palanque Institute of Research in Informatics of Toulouse (IRIT), University Toulouse 3 118, route de Narbonne, 31062 Toulouse cedex 9, France {fahssi, martinie, palanque}@irit.frAbstract. Task models produced from task analysis, are a very important element of UCD approaches as they provide support for describing users goals and users activities, allowing human factors specialists to ensure and assess the effectiveness of interactive applications. As user errors are not part of a user goal they are usually omitted from tasks descriptions. However, in the field of Human Reliability Assessment, task descriptions (including task models) are central artefacts for the analysis of human errors. Several methods (such as HET, CREAM and HERT) require task models in order to systematically analyze all the potential errors and deviations that may occur. However, during this systematic analysis, potential human errors are gathered and recorded separately and not connected to the task models. Such non integration brings issues such as completeness (i.e. ensuring that all the potential human errors have been identified) or combined errors identification (i.e. identifying deviations resulting from a combination of errors). We argue that representing human errors explicitly and systematically within task models contributes to the design and evaluation of error-tolerant interactive system. However, as demonstrated in the paper, existing task modeling notations, even those used in the methods mentioned above, do not have a sufficient expressive power to allow systematic and precise description of potential human errors. Based on the analysis of existing human error classifications, we propose several extensions to existing task modelling techniques to represent explicitly all the types of human error and to support their systematic task-based identification. These extensions are integrated within the tool-supported notation called HAMSTERS and are illustrated on a case study from the avionics domain. IntroductionTask analysis and modelling approaches have always focused on the explicit representation of standard behavior of users, leaving user error analysis for later phases in the design processes [2]. This is part of the rationale underlying task analysis which is to provide an exhaustive analysis of user behavior describing goals and activities to reach these goals. Clearly, errors, mistakes and deviations are not part of the users' goals and thus ...

Designing systems in such a way that as much functions as possible are automated has been the driving direction of research and engineering in aviation, space and more generally in computer science for many years. In the 90's many studies (e.g.[12] related to the notion of mode confusion) have demonstrated that fully automated systems are out of the grasp of current technologies and that additionally migrating functions [2] from the operator to the system might have disastrous impact on operations both in terms of safety and usability. In order to be able to design automation with a hedonic view of the involved factors (safety, usability, reliability, …) a complete understanding of operator's tasks is required prior to considering migrating them to the system side. This paper proposes a contribution for reasoning about automation designs using a model-based approach exploiting refined task models. These models describe operations with enough details in order to reason about automation and to rationalize automation designs. In this paper we present how such representations can support the assessment of alternative design options for automation. The proposed approach is applied to satellite ground segments.