Virtuality (software design)

Virtuality is a term used by Ted Nelson for what he considers the central issues of software design. "Virtuality" refers to the seeming of anything, as opposed to its reality. (This has been the dictionary meaning of "virtuality" since at least the 18th century). Everything has a reality and a virtuality. Nelson divides virtuality into two parts: conceptual structure and feel so in every field these have different roles. The conceptual structure of all cars are the same, but the conceptual structure of every movie is different. The reality of a car is important, but the reality of a movie is unimportant—how a shot was made is of interest only to movie buffs.

(Note that the goal of the paragraph above is to get across the gist of the concept. If you think about *actual* movies, quite a few of them have identical essential structures, with only trivial surface differences—there is an entire sub-industry of making the same movie, over and over, ad infinitum. The reality of the movie *is* important; if the movie was made sloppily, with janitors visible in the background cleaning up the set, and with pie-plates on fishing-rods to represent the alien invaders, this clearly screws up the feel of the movie, and probably the conceptual structure as well. Cars are also not as described here: what matters is whether it looks fast and whether it feels sporty, to the average unintelligent consumer, not whether it is actually fast in reality. Saying that the 'conceptual structure' of a fully restored rhodium-plated 1922 Rolls-Royce Silver Ghost is identical to the conceptual structure of a barely maintained primer-grey 1992 Nissan S-Cargo is false. Which gets better gas mileage, or has a tighter turning-radius, is hardly the point. This brings us back to Nelson's point, however: the reality of the Ghost and the reality of the S-Cargo do matter significantly, when you are trying to use them to get from point A to point B. If the engine conks out, you are just as stuck, no matter which one you are driving. The reality of the movie does not matter significantly: as long as suspension of disbelief is possible, and the story is magnificent, much can be forgiven.)

The feel of software, like the feel of a car, is a matter of late-stage fine-tuning (if it is worked on at all). But Nelson regards the design of software conceptual structure—the constructs we imagine as we sit at the screen—as the center of the computer field. However, the conceptual structure of almost all software has been determined by what Nelson calls the PARC User Interface, or PUI, on which Windows, Macintosh and Linux are all based. The feel is only icing on top of that.

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