Describing the UserUsers and Organizations

In user modeling it is whole populations of users that are of interest, rather than individuals. In those cases where a system is designed for a single individual, the individual is the population. Thinking in terms of user populations forces the usability professional to describe what is common across each population.

Users, User Populations, and User Profiles

A user profile is a description of a group of users as one or more user populations. The concepts discussed on this page provide a structured way to create a user profile.

A user profile describes the principal user populations of a system in terms that are relevant to understanding the needs of those users and to evaluating the usability of any proposed system designs. A user profile includes a list of user populations and a description of each population including the tasks performed by those populations.

User Responsibilities: a High-level Description of a User's Work

For the usability professional, each user population is described primarily by the responsibilities that population can fulfill. A user responsibility is a kind of task that is abstract in that it has no specific presentation associated with it. A user responsibility can be composed of other user responsibilities. Ultimately, a user responsibility is composed of tasks that do have presentation associated with them (though this is not shown in the diagram below).

Since it is a type of task, each user responsibility has a goal associated with it. The goal describes what the user hopes to accomplish when they set out to fulfill the responsibility. The user responsibility also describes the activity that must be completed to satisfy the goal.

Prioritizing Tasks in Task Modeling

Even if we could model all of the tasks performed by a user population—and ordinarily we cannot—the usability professional needs some way of prioritizing how much resource she devotes to understanding and supporting various parts of the user's world. To be useful priorities should reflect the user's priorities. For each task that is performed, the modeler must determine the frequency and criticality of that task. Frequency tells the modeler how often the task is performed. Often this is simply expressed as frequent, occasional, and infrequent or simply high, medium, and low. Criticality tells the modeler how important the task is to its users. Criticality is often expressed as high, medium, and low. Frequency and criticality are used, at least in part, to determine allocation of project resource to the various pieces of presentation. For more detail see, Use Case Diagrams, in the UML topic.

Users and Organizational Context

In many real-world situations—commerce and academic research, to name but two—it is important to understand the organizational context in which the user population performs their tasks. For the purposes of user modeling this context is described by the organizations with which a user population must interact.

An organization can be thought of as a kind of actor who delegates work—that is, the performance of one or more tasks—to its members. Organizations can also be composed of other organizations as in the hierarchical structure of many large businesses.

Organizations also do work. The kind of task performed by an organization is called a process. Since a process is a kind of task, it also has a goal and a description of the work needed to achieve that goal. Processes are composed of other processes and of user responsibilities corresponding to the tasks performed by an organization's members.

A Formal Model of Users and Organizations

The figure below is a UML class diagram depicting user populations and the organizations within which those users work.

Figure: a UML class diagram, over 650 pixels wide—click here to open it in a separate window.

The preceding diagram shows the elements that model the actors in our user's world: organizations and user populations. Organizations may contain other organizations and they may contain members who are user populations—think of them as the job titles in a business organization. Organizations and User Populations each are responsible for a set of tasks: processes and user responsibilities, respectively. And, for each combination of actor and task, we record the frequency and criticality with which that actor performs that task.