Task Model

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Task Models for User Interface Design

Task Models describe how to perform activities to reach users' goals.

Of the relevant models in the human-computer interaction field, task models play an important role because they represent the logical activities that should support users in reaching their goals. Knowing the tasks necessary to goal attainment is fundamental to the design process. The need for modelling is most acutely felt when the design aims to support system implementation as well. If we gave developers only informal representations (such as scenarios or paper mock-ups), they would have to make many design decisions on their own, likely without the necessary background, to obtain a complete interactive system. Task models represent the intersection between user interface design and more systematic approaches by providing designers with a means of representing and manipulating an abstraction of activities that should be performed to reach user goals.

There are many reasons for developing task models. In some cases the task model of an existing system is created in order to better understand the underlying design and analyse its potential limitations and how to overcome them. In other cases designers create the task model of a new application yet to be developed. In this case, the purpose is to indicate how activities should be performed in order to obtain a new, usable system that is supported by some new technology.

Task models can be represented at various abstraction levels. When designers want to specify only requirements regarding how activities should be performed, they consider only the main high-level tasks. On the other hand, when designers aim to provide precise design indications then the activities are represented at a small granularity, thus including aspects related to the dialogue model of a user interface (which defines how system and user actions can be sequenced). The subject of a task model can be either an entire application or one of its parts. The application can be either a complete, running interactive system or a prototype under development. The larger the set of functionalities considered, the more difficult the modelling work. Tools open up the possibility of modelling entire applications, but in the majority of cases what designers wish to do is to model some sub-sets in order to analyse them, and to identify potential design options and better solutions. Task models can be used for many types of applications: there are applications that are clearly goal-oriented and so the tasks are clearly structured, other applications support a wide range of options open at any time, with the continuous possibility for the users to freely decide what to do and how to do it, in this case the task model should not be particularly structured in order to allow such possibilities.


Many task models, task analysis methods, and supporting tools have been introduced in the literature and are widely used in practice. Below you can find formal descriptions of different representations of task models. For this purpose, a meta-model of each task model is expressed as a UML class diagram. More details can be found in the further readings section.







Further Readings

Annett, J., & Duncan, K. (1967). Task analysis and training design. Occupational Psychology, 41, 211–227.

Barthet, M.-F., & Tarby, J.-C. (1996). The Diane+ method. In J. Vanderdonckt, (Ed.), Computer-aided design of user interfaces (pp. 95–120). Namur, Belgium: Presses Universitaires de Namur.

I.Breedvelt, F.Paternò, C.Severiins, “Reusable Structures in Task Models”, Proceedings Design, Specification, Verification of Interactive Systems ’97, Granada, June 97, pp.251-265, Springer Verlag.

Giese, M., Mistrzyk, T., Pfau, A., SzwillusG. & von Detten M. (2008), "AMBOSS: A Task Modeling Approach for Safety-Critical Systems", Pisa : Springer-Verlag, Berlin, 2008. 7th Int. Workshop on Task Models and Diagrams TAMODIA'2008. http://mci.cs.uni-paderborn.de/pg/amboss/

Guerrero, J., Vanderdonckt, J., Gonzalez Calleros, J.M. (2008), FlowiXML: a Step towards Designing Workflow Management Systems, "Journal of Web Engineering", Vol. 4, No. 2, 2008, pp. 163-182.

Guerrero Garcia, J., Vanderdonckt, J. (2008), Towards a Multi-Users Interaction Meta-Model. IAG Working Paper 08/25, Université catholique de Louvain, 2008.

John, B. E.,&Kieras, D. E. (1996). The GOMS family of user interface analysis techniques: Comparison and contrast. ACM Transactions on Computer-Human Interaction, 3, 320–351.

Limbourg, Q., Vanderdonckt, J. (2002), Comparing Task Models for User Interface Design, Chapter 6, in Diaper, D. and Stanton, N. (Eds.), " The Handbook of Task Analysis for Human-Computer Interaction " Lawrence Erlbaum Associates, Mahwah, 2002.

Limbourg, Q., Vanderdonckt, J., Michotte, B., Bouillon, L., López Jaquero, V. (2004) UsiXML: a Language Supporting Multi-Path Development of User Interfaces, Proc. of 9th IFIP Working Conference on Engineering for Human-Computer Interaction jointly with 11th Int. Workshop on Design, Specification, and Verification of Interactive Systems EHCI-DSVIS’2004 (Hamburg, July 11-13, 2004). LNCS, Vol. 3425, Springer-Verlag.

Limbourg, Q. (2004) Multi-Path Development of User Interfaces. Ph.D Thesis, Université catholique de Louvain, 2004.

Mahfoudhi, A., Abed, M.,&Tabary,D. (2001). From the formal specifications of user tasks to the automatic generation of the HCI specifications. In A. Blandford, J. Vanderdonckt, & P. Gray, (Eds.), People and computers XV (pp. 331–347). London: Springer.

UsiXML Consortium Web site

G. Mori, F. Paternò, C. Santoro, “CTTE: Support for Developing and Analysing Task Models for Interactive System Design”, IEEE Transactions on Software Engineering, pp.797-813, August 2002 (Vol. 28, No. 8), IEEE Press.

Paternò F., Model-based Design and Evaluation of Interactive Applications, Springer Verlag, ISBN 1-85233-155-0, 1999.

Paternò F., ConcurTaskTrees: An Engineered Notation for Task Models, Chapter 24, in Diaper, D., Stanton, N. (Eds.), The Handbook of Task Analysis for Human-Computer Interaction, pp.483-503, Lawrence Erlbaum Associates, Mahwah, 2003.

F. Paternò, C. Santoro), S. Tahmassebi, “Formal Models for Cooperative Tasks: Concepts and an Application for En-Route Air Traffic Control”, Proceedings DSV-IS’98, pp.71-86, June’98, Abingdon, Springer Verlag.

F.Paternò, C.Santoro, V.Sabbatino, Using Information in Task Models to Support Design of Interactive Safety-Critical Applications, Proceedings AVI’2000, pp.120-127, ACM Press, May 2000, Palermo.