Collaborative Environments: Accessibility and Usability for Users with Special Needs - Community-Built Databases: Research and Development - page 325

Table 13.3 Nielsens's
heuristic principles

N Heuristic

1 Visibility of system status

2 Match between the system and the real world

3 User control and freedom

4 Consistency and standards

5 Recognition rather than recall

6 Flexibility and efficiency of use

7 Display all but needed information

8 Error prevention

9 Help users recognize, diagnose, recover from errors

10 Help and documentation

maps the criteria into usability metrics. The factors describe different facets of the
usability by means of user-oriented attributes identified in existing standards and
models. The eleven factors are: efficiency, effectiveness, productivity, satisfaction,
learnability, safety, trustfulness, accessibility, universality, usefulness, and accept-
ability. The criteria have subfactors that are directly measurable via a set of metrics.
Metrics are numeric values that summarize the status of specific user interface
attributes. They are faster, cheaper, and less ambiguous than other usability evalu-
ation attributes, [ 23 ] but their context of use can be influenced by a specific category
of users, tasks, or environments.
The QUIM model does not cover all models proposed in the literature. For
example, the Polillo quality model for Web sites [ 25 ] is not taken into account
even if the usability factors of the two models are quite similar. The Polillo quality
model considers some aspects of Web design activities (like architecture, content,
or management characteristics) that can be also described using QUIM factors or
criteria. For instance, the architecture characteristics deal with issues related to the
navigability or the consistency of Web sites and the QUIM model also offers
specific criteria to represent them.
The consolidated QUIM model provides design principles able to bring the
designer's attention to issues that should be considered in order to develop success-
ful interactive applications. Current interactive systems have to support powerful
functionalities, but also a simple and clear interface; they have to be easy to use and
to learn; they have to be flexible but also provide good error handling. Under this
prospective, a consolidated model for detecting and assessing usability factors
can be employed as a guideline for designing interactive systems because it con-
solidates the experiences, points of view, and studies proposed within several
Human- Computer Interaction and Software Engineering communities [ 27 ].

13.3.2 Accessibility

Accessibility is particularly important in Web-based collaborative environments
since accessible user interfaces allow users with disabilities to take an active part in
the process of knowledge creation.