Methodology II: Cognitive Dimensions and the Gulfs - Foundations for Designing User-Centered Systems - page 327

Chapter 12
Methodology II: Cognitive Dimensions
and the Gulfs
Abstract This chapter introduces two useful high-level approaches that summa-
rize a wide range of aspects of users: how users interact with artifacts and how
users perform tasks. A type of analysis, Cognitive Dimension/dimensions, pro-
vides a way to represent common and important aspects of interface design. The
dimensions are used to describe and then evaluate interfaces. Norman has a similar
description of user behavior based on how hard it is to understand the state of the
interface (the Gulf of Understanding) and how hard it is to perform an action in an
interface (the Gulf of Execution). Both approaches are useful techniques for
thinking about, planning, and performing interface design.
12.1 Introduction
So far we have presented several methods and techniques for analyzing Human-
System Interaction, including task analysis as a general tool, and GOMS and the
KLM as more detailed formal approaches for use prior to user testing. Most of the
methods we have presented are applied at a low level of abstraction. In contrast,
the Cognitive Dimensions (of Notations), usually just referred to as Cognitive
Dimensions or CDs (e.g., Blackwell and Green 2003 ; Green 1989 ), was developed
as a mechanism for discussing and analyzing systems at a higher level of
abstraction.
The CDs are based on the assumption that it is useful to have a language for
discussing design. One way of trying to understand design is to describe the object
that is being designed, and the trade-offs that the designer faces using a small
number of fundamental dimensions. These dimensions can then provide a common
language (sometimes called an ontology) for discussing usability problems, as well
as a means of comparing aspects of interface and system design, and for com-
paring whole designs. Thus, the CDs can be seen as a way of providing a common
ontology for naming aspects of design as well as for naming design trade-offs.