Software Engineering-Task Analysis and System Model


Task analysis for interface design uses either an elaborative or object-oriented approach but applies this approach to human activities.

Task analysis can be applied in two ways. As we have already noted, an interactive, computer-based system is often used to replace a manual or semi-manual activity. To understand the tasks that must be performed to accomplish the goal of the activity, a human engineer must understand the tasks that humans currently perform (when using a manual approach) and then map these into a similar (but not necessarily identical) set of tasks that are implemented in the context of the user interface. Alternatively, the human engineer can study an existing specification for a computer-based solution and derive a set of user tasks that will accommodate the user model, the design model, and the system perception. Regardless of the overall approach to task analysis, a human engineer must first define and classify tasks. We have already noted that one approach is stepwise elaboration.

For example, assume that a small software company wants to build a computer-aided design system explicitly for interior designers. By observing an interior designer at work, the engineer notices that interior design comprises a number of major activities: furniture layout, fabric and material selection, wall and window coverings selection, presentation (to the customer), costing, and shopping. Each of these major tasks can be elaborated into subtasks. For example, furniture layout can be refined into the following tasks: (1) draw a floor plan based on room dimensions; (2) place windows and doors at appropriate locations; (3) use furniture templates to draw scaled furniture outlines on floor plan; (4) move furniture outlines to get best placement; (5) label all furniture outlines; (6) draw dimensions to show location; (7) draw perspective view for customer. A similar approach could be used for each of the other major tasks.

Subtasks 1–7 can each be refined further. Subtasks 1–6 will be performed by manipulating information and performing actions within the user interface. On the other hand, subtask 7 can be performed automatically in software and will result in little direct user interaction. The design model of the interface should accommodate each of these tasks in a way that is consistent with the user model (the profile of a "typical" interior designer) and system perception (what the interior designer expects from an automated system).

An alternative approach to task analysis takes an object-oriented point of view. The human engineer observes the physical objects that are used by the interior designer and the actions that are applied to each object. For example, the furniture template would be an object in this approach to task analysis. The interior designer would select the appropriate template, move it to a position on the floor plan, trace the furniture outline and so forth. The design model for the interface would not provide a literal implementation for each of these actions, but it would define user tasks that accomplish the end result (drawing furniture outlines on the floor plan).
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