Usability and glossary

Quality in Use is Defined as 'The capability of a system to enable specified users to achieve specified goals with effectiveness, productivity and satisfaction in specified contexts of use.'

Usability is the extent to which the product meets user needs, and includes issues such as appropriate functionality, compatibility and reliability as well as security and accessibility.  The conceptual model used to present the functions contributes about 60% of the ease of use whereas the details of the look and feel contributes only 10% (IBM, 1992). Activities concerning the identification and specification of functions to support user tasks should therefore, from an end user point of view, be part of the whole user-centred design process.

Differences between the Usability Maturity Model and usability engineering approaches to usability

Proce ss Numb er





System strategy

Plan and manage HCD

These organisational processes have not traditionally been considered within the scope of usability and are only partially covered in ISO 13407.  However, experience has shown (Clegg et al, 1997) that organisational commitment is essential to the successful implementation of user-centred design, and the activities listed under HCD.1 “Ensure HCD content in system strategy” and HCD.2 “Plan and manage the HCD process” detail how this can be achieved.


Introduce and operate the system

Activities such as determining the impact on the organisation and users, customisation, training and support are essential for successful implementation, but have rarely been considered within the scope of usability, and indeed are not included in ISO 13407.


Specify user and organisational requirements

Usability requirements activities are often limited to the user interface (Nielsen 1993, Mayhew 1999), while ISO 13407 and ISO TR 18529 are concerned with human requirements for the whole system.


Produce design solutions

Two of the recommended activities contributing to design are missing from many usability engineering methodologies, but central to Ergonomics and Human Factors: allocation of function and a definition of the overall experience of use of the system.




Understand context of use

Evaluate designs against requirements

This is a central area of concern for usability engineering, although the standards are more explicit about the need to verify that the context used for evaluation is sufficiently close to the intended context of use. Context of use is completely missing from traditional systems and software engineering.


There are established ways to measure the attributes of quality in use or usability. These can be found at the UsabilityNet site or the University College Cork site (see the links page for the URLs).


Lloyd’s Register of Shipping and Process Contracting Limited © 2003