My Search for Usability Design

Is Design = Usability?
Design --> Usability?
Design=Form and Usability=Function?
Are there any models for social usability?

I have been twisting my brain searching for the answer to the question "What is usability?" In this philosophical search I am reminded of the quest to define "What is quality?" in the book Zen & The Art of Motorcyle Maintenantance. Is there "a" answer?

I have been searching the research literature to find what the scholars say. In the Human Computer Interaction field Jacob Nelisen system acceptability model (see fig below) and Ben Schneirdman's universal usability are the recent experts on the topic.

Here is a concept map of Nielsen's framework






















Jeng's What Is Usability in the Context of the Digital Library and How Can It Be Measured? (2005) prepared this literature review chart of the what others name as the attributes to usability.