Jeff Davis <pgsql@j-davis.com> wrote:
> Trying to incorporate a "start value" is adding extra information
> in there, and it's not really a part of the same algebra. It
> sounds more like a contiguous sequence with a "start value" and a
> "current value" to me.
Well, in the receipt number example there are multiple ranges in use
for each year, and ranges for multiple years. If we get to the idea
of a multi-ranges, this would be very handy for certain types of
reports -- especially for auditors. It's not that we can't do with
with discrete begin and end columns -- we do that now; but it seemed
a potentially beneficial use of ranges for us, if they can represent
the needed states. People already talk about these as ranges, just
in terms of the common English understanding of the word.
Perhaps it was a mistake to get so concrete rather than conceptual
-- basically, it seems like it could be a useful concept for any
planned or scheduled range with an indeterminate end point, which
you want to "reserve" up front and record in progress until
complete. The alternative would be that such "ranges to be" have a
parallel "planned start value" column of the same type as the range,
to be used as the start of the range once it is not empty. Or, as
another way to put it, it seems potentially useful to me to have an
empty range which is pinned to a location, in *addition* to the
unpinned empty ranges such as would be needed to represent the
intersection of two non-overlapping ranges.
Of course, the *most* useful places for our shop to have ranges are
temporal. Many (most?) of those are situations where you start with
a range with an unknown end and later (often years later) fill in
the end of the range based on some event which finally closes it.
Again, two discreet dates with a null-capable end-date work, but I
can see where ranges could potentially be more powerful.
-Kevin