Conceptual model


Years ago, I championed “User-Centered System Design,” based upon the point that designers had to focus their attention upon the users of their systems. I diagrammed the interaction between designer and user as a triad:

The designer’s model, the system image, and the user’s model. For people to use a product successfully, they must have the same mental model (the user’s model) as that of the designer (the designer’s model). But the designer only talks to the user via the product itself, so the entire communication must take place through the “system image”: the information conveyed by the physical product itself. (Originally published in Norman & Draper’s User Centered System Design (1986), and reused frequently thereafter: The Design of Everyday Things (1988, 2003) and Emotional Design(2004).

I have long maintained that the appropriate way to design a complex system is to develop a clear, coherent conceptual model (ideally the same as the designer’s conceptual model) and to design the system so that the user’s mental model would coincide. I had always assumed this would be done through the design of the “System Image”: the artifact plus any auxiliary material, such as manuals and help systems.

DeSousa makes a major advance in our understanding of the communication model. If the designer explains the reasoning behind the model, the user will find the task of uncovering the conceptual model much easier. In other words, what we need to provide to people is reasons, not just methods.

Systems usually try to convey the actions that need to be taken at any point in a sequence. A major driving force in the development of graphical user interfaces — the GUI — was to make all possible commands visible, so at any point a person could discover what to do simply by looking through the set of possibilities. The technique of “graying out” menu items that are not applicable at the moment is a communicative tool: indicating the existence of the command while simultaneously indicating that in this situation, it does not apply. Although GUIs were a major step forward, they simply providing information about the set of possibilities, not about the reasoning. Thus, if a grayed-out command appears to be precisely what the person is searching for, the system simply communicates its non-availability: it does not suggest why it is not available, nor how to change it to be available.

Human beings are explanation machines. We are always trying to understand the world around us, and we make up stories to explain the occurrences we experience. If there is sufficient evidence or knowledge, these stories are reasonably accurate, but in the absence of such information, the story — in other words, the explanation — is apt to be wrong. In many cases, the person simply cannot construct an adequate explanation, not even for themselves, which means they remain puzzled and are apt to have the same difficulty every time they encounter the situation.

Conceptual Models as Stories

What are conceptual models? I think the easiest way to connive of them is as stories, stories in context. A model is a story that puts the operation of the system into context: it weaves together all of the essential components, providing a framework, a context, and reasons for understanding. Without this story, without this conceptualization, the operation of something becomes a set of memorized actions, but without reason or purpose except “this is how it is done.” Although we do operate many of the devices in our lives as learned operations, if there is any complexity to the device at all, then those operations are difficult to learn and prone to error. Worse, when things go wrong – as things invariably will – the lack of a story, of a context, and most importantly of all the lack of any explanation or reasons why the operations are being performed, means that the poor person cannot cope: without understanding, new sequences are difficult to derive, escape mechanisms, recovery strategies and the all-important “work-arounds” are difficult if not impossible to discover.


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