Hi, I have my own definition for usability: usability is one intangible, important & integrated art & science attached to each of the distinct processes involved in the development of any product or system.
If you segregate usability form any of the processes and treat it as one seperate entity, it would be a useless piece of knowledge - actually I wouldn't even call it usability then! Usability in today's world is fast becoming the baseline of everything but regretfully few organisations are still treating it as a seperate entity. Some have dedicated teams for this as a seperate deptt. But is it helpful? Some say yes, but are they actually utilizing these resources effeciently? I don't think so. The actual beauty of usability is when you don't need a seperate team, instead every team has one or more volentiars responsible to oversee it.
If usability is all where would PET go?
Just kidding !
I feel usability is one of the different ways of guiding the solution. Solution is independent of the path. But a testified path makes one surer of the solution.
usability takes approach of reaching the solution by understanding user as a cognitive processor.
Design thinking is fuzzy thinking, a given problem has multiple solutions which can be prioritized and selected from.
These solutions also have a temporal nature. Remember 'usability is no longer enough'.
As a discipline evolves, newer perspectives and ways of finding solutions emerge.
But above all the technology itself is evolving along with the evolving users so the situation is complex..
It is about empowering yourself by tools and aids to thinking the solution.
Usability is one Process, One approach, One tool.which was a high end one, once upon a time.... but sorry.. today it is a basic tool.
A must have but not ALL. surely not all.
So usability is NOT all !
also neither it is 'part' .. I feel one has to merge approaches in a seamless fashion so as the 'parts' to become indistinguishable.
Of course we acquire such skills and knowledge in parts ... but in practice, when they become art.. there are no parts :).
But it also depends on what kind of products one is designing.
A pure application, for doing repetitive tasks? Like booking online tickets by railway officers at the reservation counter? Focus primarily on usability.. just make the system efficient!
But if you are selling something online... users are not the trained officers of the railway counter.
You need to persuade the users to buy your products and give a satisfaction in having done so.. so that they become loyal and visit you again.