Conceptual models and composition
In this section, we’ll look at two related concepts that help us design systems
spanning multiple devices.
Conceptual models refer to the way humans understand the overall system
(and its interfaces) to work. Users need some understanding of how the system
works in order to figure out how to interact with it. As we saw above,
composition is a dimension of interusability. It refers to the way user-facing
functionality is distributed between different devices: which device does what.
The two concepts are related in cross-platform design: understanding which
device does what is part of forming an effective conceptual model.
Conceptual models
The user model and the design model
The conceptual model may refer to the way the user understands the system, or
the way the designers (or engineers) think about the system. Users develop a
mental model of the system (a user model) that enables them to understand
what it does, how to interact with it, and how it will behave. At first, this will
be based on prior experience of other systems or similar activities. Over time
they will develop the model through their experiences with the system itself.
The way the designers or engineers think about the system will be reflected in
the design model (this distinction was defined in Don Norman, 1988)^3.
As Norman puts it: ‘The problem is to design the system so that, first, it
follows a consistent, coherent conceptualization - a design model – and
second, so that the user can develop a mental model of the system – a user
model – consistent with the design model.’
The similarity between the design model and the user’s mental model is a core
determinant of usability in any system, not just IoT. How easy is it for the user
to figure out how to achieve a particular goal using the system (which Norman
(^3) Norman, Donald (1988). The Design of Everyday Things. New York: Basic Books.