The term “usability” is defined in the international standard ISO 9241-11 “Guidance on Usability”:

   The extent to which a product can be used by specified users to achieve goals with effectiveness, efficiency and satisfaction in a context of use.

ISO 9241 is a standard with 28 parts, and talks about the ergonomics of computer-related products. The concepts behind usability as a quality aspect in software are further entrenched in ISO/IEC 9126 standard on “Software Engineering – Product Quality”. ISO 13407 is a development-oriented standard on “Human-centred design processes for interactive systems” and seeks to provide guidance on human-centred design activities throughout the life cycle of computer-based interactive systems. The principles are thus well understood and have been researched profusely within the area of Human Computer Interaction (HCI).

Web 2.0 has however added a new dimension to usability. Users no longer fit a “specified” profile (as thought out in the definition quoted from ISO 9241-11 mentioned above) which may be used to form a clear design approach. Instead, Digital Natives want to interact with Web systems in a way that they can personalise their experience – products need to evolve and adapt to the individual user’s specific requirements. Myhill (2004) borrows the term ‘Desire Line’ from the area of urban planning to describe this concept as follows:

   A desire line normally refers to a worn path showing where people naturally walk. Desire lines are an ultimate expression of human desire or natural purpose. An optimal way to design pathways in accordance with natural human behaviour, is not to design them at all. Simply plant grass seed and let the erosion inform you about where the paths need to be. Stories abound of university campuses being constructed without any pathways to them. Planners responsible earn great respect for their cunning in allowing the desire lines to form before finalizing the construction of the paved pathways.

Bevan and Curson’s (1998) tutorial on Planning and Implementing User Centred Design makes reference to Bevan’s (1996) Usability Context Analysis methodology for “gathering and documenting information about the characteristics of the intended users, tasks and environments.” This is based on the recommendations of the aforementioned ISO 13407. While this remains recommended even in the development of Web 2.0 systems, the concept of “desire lines” and thus the ability for Web systems to adapt to the user’s needs through usage itself, becomes ever more relevant. Myhill (2004) cites Belam, Martin (2003) who describe a usability aspect of the BBCi Web Site where the “web user interface and the information structure, such as their subject index” are adapted “based on what people are typing into the Search facility” which are, in turn, checked for “desire lines” on an hourly basis. The concept of tailoring the site to ‘hits’ has now evolved to tailoring the site to the individual ‘user’. This ‘intelligence’ is in fact now considered standard – Google uses it to tailor ads, Amazon uses it to recommend other purchases you can make, etc…

In yesterday’s post, I mentioned Roto (2007) as I believe it is one of the key works of the UX Manifesto.  Roto, from Nokia Research Centre, notes – and I agree – that it is important to note the subjectivity introduced by “experience” since this makes each user a different stakeholder to product design and each experience a personal perception. Usability, as may be confirmed by the definition in ISO 9241-11, is what Roto calls “a product attribute”. A User Experience (UX) starts with the expectations raised by peers, is formed during the interaction with the product and continues to be affected beyond the interaction stage by all that we all that I hear about it or its manufacturer. In this sense, Usability is only a subset of UX.