The user's conceptual model of a system is a mental image that each user subconsciously forms as he or she interacts with the system. People create mental models by putting together sets of perceived rules and patterns in a way that explains a situation. A typical person cannot draw or describe his or her mental models and in many situations the person is not even aware that these mental models exist.
A mental model does not necessarily reflect a situation and its components accurately. Still, a mental model can help people predict what will happen next in a given situation, and it serves as a framework for analysis, understanding, and decision-making.
Each user's conceptual model is based on his or her expectations and understanding of what a system provides in terms of functions and objects, how the system responds when the user interacts with it, and the goals the user wants to accomplish during that interaction. These expectations, understandings, and goals are influenced by the user's experiences, including interaction with other systems, such as typewriters, calculators, and video games.
Because each user's conceptual model is influenced by different experiences, no two conceptual models are likely to be the same. Each user looks at a user interface from a slightly different perspective.
The problem for the interface designer is to design an interface that users find predictable and intuitive when each user is approaching the interface from a different perspective. To come as close as possible to matching users' conceptual models, designers should find out as much as they can about users' skills, motivations, the tasks they perform, and their expectations. This process involves the following tasks:
This is an iterative process that may require many cycles. As the design progresses, users may identify aspects of the interface that are difficult to learn, that are counter-productive, or aspects they simply do not like.
Through interaction with the user interface, users' conceptual models may be expanded, which in turn may cause them to realize new requirements that they had not thought of before. As users provide this level of information to the designer, the picture of their conceptual models will become clearer.
Conceptual models of an object-oriented user interface consist of the objects, properties, behaviors, and relationships of those objects, that are involved in the user's interaction with the system.
When users first interact with a new interface, they are likely to attempt to understand its operation in terms of roles and relationships they already understand. In other words, we each carry with us a current conceptual model. Where existing models lead to correct expectations, the model is reinforced and the user will feel the interface is intuitive. When results are not as expected, the user may rationalize by inventing new roles and relationships in their model, in order to explain observed behavior.
If the user-supplied extensions are accurate, they will be reinforced through interaction with similar aspects in different parts of the system. Otherwise, they are likely to cause confusion. Sometimes users develop superstitions about the interface. These superstitions result from incorrect rationalizations about how and why the interface appears to behave as it does. Superstitions are likely to cause unexpected results in response to the user's actions and further contradict the user's intuition. This can lead to a breakdown in understanding and trust by the user. The use of metaphors and consistency by designers can help user's correct and extend their conceptual models.
A new interface should resemble something familiar to help users get started and then allow them to explore new concepts. It is often said that a characteristic of a good user interface is that it is intuitive. Perhaps when used in this sense intuition can best be characterized as a good match between the user's conceptual model and the designer's model.
By using metaphors, designers can take advantage of users' experience and allow a user to rely on intuition while expanding the user's conceptual model to take advantage of new capabilities provided by the interface. Interfaces that use metaphors and allow users to safely explore the computerized environment are popular for this reason.
For example, a computerized car dealer application might provide a worksheet object to be used by a salesperson in the task of selling a car. The computerized worksheet would contain the same information and would be used in the same way as a paper worksheet. Like the paper worksheet, the worksheet object would allow the salesperson to enter the car's price and stock number, the customer's name and address, and information about the proposed terms of the sale.
However, the computer-based worksheet could also expand the salesperson's conceptual model by providing capabilities that go beyond those of a paper worksheet. Instead of typing information into the worksheet one field at a time, the salesperson might simply "drag and drop" a car object onto the worksheet. The fields in the worksheet that are relevant for the car being sold would be automatically filled in by the associated fields from the car object. Monthly payments and finance charges could be calculated automatically. Instead of having to hand a paper worksheet to the sales manager for approval, the salesperson could drag and drop the worksheet into a specific mail outbasket to have it automatically sent to the sales manager through the dealer's computer network.
This worksheet object would not only meet the salesperson's expectations, it would go beyond them. It is an object that the salesperson expects to use during the task of selling a car, it has behaviors and characteristics that the salesperson is accustomed to, and it provides additional value through the use of a computer.
In this example, the worksheet object acts as a metaphor for an object that already exists in the salesperson's conceptual model of a car dealership and the task of selling cars. It is an object with which the salesperson is already comfortable, yet it provides additional capabilities that make the salesperson's job easier than using a paper counterpart.
Users' conceptual models constantly evolve as they interact with an interface. Just as users influence the design of a product, the interface design influences and modifies users' concepts of the system. Designers can help users develop an accurate conceptual model by using well defined distinctions between objects and by being consistent across all aspects of the interface.
For example, given an object-oriented car dealer application, the salesperson would open and work with familiar objects, instead of starting and running computer programs, opening files, and so forth. This object-oriented approach has fewer concepts for the salesperson to deal with and matches the salesperson's real world better than one in which a task is accomplished by starting applications and opening files.
Naturally, the conceptual model of a salesperson who is already familiar with using a graphical computer interface requires little modification. This salesperson would already know how to use icons, windows, menu bars, and push buttons.
In any case, the distinctions between objects must be clear and useful, and the interface must be consistent. Otherwise, the users' conceptual models will be modified in ways other than those intended by the interface designer.