On 21/02/2018 13:55, Andy Mabbett wrote:
Consider, for instance:
an "instance of" a "telephone numbering plan" (Q103903)
Hum, this becomes a bit tricky − maybe it's actually a legitimate
identifier? I don't see any error in the chain…
(Actually the uniqueness is
debatable, I don't think DNS is meant to enforce any uniqueness at all,
as it is very common for a website to have multiple domain names.
Surely the uniqueness works in the other direction? A UID identifies
one unique subject; the subject can have multiple UIDs.
Oh that's interesting! I would intuitively say that "identifier" already
includes that uniqueness (otherwise we cannot really say that it
identifies anything). Of course a given subject can have UIDs in
different identifier schemes, issued by different bodies.
So I would say the "unique" bit in "unique identifier" refers to the
other direction (an entity has at most one such identifier in the
particular scheme). That is the uniqueness that is hard to obtain: it is
hard to ensure that a large database does not contain duplicates (and it
is much easier to ensure that a given string points to at most one
record in that database). So, when we say "unique identifier", I would
intuitively say that the uniqueness we stress is the valuable one.
But I might be wrong! What do others think?