On 25 November 2010 11:02, Jakob Voss <[log in to unmask]> wrote:
[...]
For clarity's sake, could anyone who thinks there is a really clear
concept that is not 1 or 2 above clarify exactly what it is, and how it
differs from the other similar concepts?

There could be:

3. A combination (set) of values. This could be different from a range, for instance if {2000-12,2000} is the set of the month December 2000 and the year 2000, which is not the same as the year 2000.

Maybe that's OK, but I don't yet understand the practical application of a set of date/time values. Perhaps it would be clearer (to me at least) to have some concrete examples?

4. An approximate value. Approximation is a flag that marks a value independent from other properties. The concept is based on fuzzy set theory. For instance the approximate year 2000~ is not equal to any strict interval.

5. a value that is questionable

This is really what I am questioning. Do you (does anyone) think that fuzzy set theory is really something we want to have as one of the foundations of the spec? I certainly have never yet got the sense that fuzzy set theory was uncontentious, and I question the wisdom of basing any standard on a contentious foundation. But maybe this is for debate.

Leaving aside fuzzy set theory, it isn't hard in many cases to translate an approximate value into an expression that it is one value from within a range. Can anyone propose any generally acceptable distinction between an approximate value with no definite range, and a value that is questionable? At present I cannot imagine any pragmatic difference.

A value that is questionable is really the beginning of an account that cannot possibly be captured in a spec like this. What evidence is the supposed value based on? What is the potentially contradictory evidence? Etc. To me, the semantics of this is essentially "best guess", supported by other material.

So, for a single value date/time, my personal conclusion is that there are just four cases:
1. A definite particular value
2. One value drawn from a specified range (copes with cases like "one Christmas in the 1890's")
3. One point in a specified interval
4. A "my/our/best guess" value.

Are all intervals adequately represented by exactly one start and end value, from the cases above?

For ranges, I'm aware that others have spent a lot of time thinking about this. But isn't a range just a discrete set formulated in a particular way? I'll try to look again at what there is in the spec draft.

Simon

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Simon Grant
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