Task-Centered System Design

Task-centered system design, a variation of user centered design, is a technique that allows developers to design and evaluate interfaces based on users' real-world tasks. As part of the design, it becomes a requirements analysis (with the requirements being the tasks that need to be satisfied). As part of evaluation, the evaluator can do a walk-through of the prototype, using the tasks to generate a step by step scenario of what a user would have to do with the system. Each step in the walkthrough, the evaluator asks the questions: is it believable that a person would do this; and does the person have the knowledge to do it? If not, then a usability bug has been found.

An assignment on task-centered design and prototyping  provides students with hands-on practice in task articulation and prototype walkthrough (see the lecture notes).

Overheads

• Task-centered system design: [Acrobat] [PowerPoint]

Topics covered

• Task-centered system design
  • The task-centered process
  • Developing task examples
  • Task scenarios and walkthroughs

Required Readings 

• Greenberg, S. (2002) Working through Task-Centered System Design. in Diaper, D. and Stanton, N. (Eds) The Handbook of Task Analysis for Human-Computer Interaction. Lawrence Erlbaum Associates: [Acrobat]
• Cooper, A. (1999) The inmates are running the asylum (Chapter 9). Sams (Macmillan), Excerpt on Personas

Optional Readings

• Cooper, A. (1999) The inmates are running the asylum (Chapter 10& 11). Sams (Macmillan), Excerpt on Personas
• Baecker, Grudin, Buxton and Greenberg Chapter 3: Considering Work Contexts in Design and other readings in that section (p.187-272). This chapter focuses on the interplay between the design of computer systems and applications, as well as the social and organizational settings in which they are to be used. It goes far beyond the sometimes simplistic view of task-centered system design by considering the entire work context: from user centered, to organization-centered, to the sociology of work, and to workplace computerization.
• The online version of Lewis and Rieman's book (from The Handbook of Task Analysis for Human-Computer Interaction) which Greenberg's book chapter is based upon.
• An additional resource: A description of the task-centered process and how each part of that process may look in your portfolio.

In-class teaching tips

I develop an example of task-centered system design by using an imaginary client called "Cheap Shop", a catalog-based store. The situation is that Cheap Shop's customers now browse through paper catalogs and then place their orders by filling in a form and giving it to the clerk. Cheap Shop is considering replacing the paper forms by a computer interface. An initial design is proposed (provided in the exercise mentioned above). The task examples presented in the exercise are used to develop usage scenarios. The class then evaluates the design by a walking a user through the example tasks step by step. At first glance the system may appear to be adequate but after completing the task-centered evaluation many deficiencies are discovered.

Major sources used to prepare lecture material

• The shareware book by Lewis and Rieman  describes the entire task-centered system design process. 
• Cognitive and pluralistic walkthroughs are highly related techniques that influence the way I present this material.
  • Bias, R.G. (1994) Chapter 3: The pluralistic usability walkthrough: Coordinated Empathies. In J. Nielsen and R. Mack (Eds) Usability Inspection Methods, p63-76, Wiley and Sons
  • Wharton, C., Rieman, J., Lewis, C. and Polson, P. (1994) Chapter 5: The cognitive walkthrough method: A practitioner's guide. In J. Nielsen and R. Mack (Eds) Usability Inspection Methods, p105-140, Wiley and Sons.
• Sato, S. and Salvador, T. (1999) Playacting and focus troupes: Theatre techniques of creating quick, intense, immersive, and engaging focus group sessions. Interactions, 6(5), September/October describes a techniques for discovering uses of brand new products with no precursors.
• The book Contextual Inquiry by Beyer and Holtzblatt (Morgan Kauffman Press) describes a detailed methodology for articulating tasks, and is highly recommended if you are analyzing complex situations.