Re: UUIDs (Was: Software implementing Gentech Genealogical Data Model)

On Tuesday 09 June 2009 22:49, Gordon Burditt (gordonb.zl2k5@xxxxxxxxxxx)
opined:

But, back to what I've been saying, the concept of universally unique IDs
implies such an id is valid for the same entity, whatever that entity is,
everywhere that entity is found - in multiple databases on _my_ machine,
on Alice's machine, clear through to Zeke's machine.

I disagree. UUIDs have a large number space such that every
genealogist can give every person in the world that ever lived a
UUID, without having any duplicates. A given person, or birth,
death, or marriage record, may have billions of UUIDs referring to
the same person or fact.

OK, I understand RFC 4122 UUIDs .. I think. What you suggest above implies
that I want to slap what's essentially a label on a record, that label
being generated essentially randomly and using one specific type of RFC
4122 uid. But what I've posited elsewhere is an identifier generated by a
known mechanism, such as MD5, from some combination of data points for an
individual. Such an identifier falls within the definition in the RFC of
another form/type of uid. For the sake of argument, let's say that the
string we submit to MD5 is a concatenation of surname, first/christian
name, day, month and year of birth, city, county, state and country of
birth, and maybe father's christian name and mother's maiden name. Now, a
string composed of those elements will hash using MD5 to a particular
32-digit hexadecimal value which is theoretically unique. If and only if
your information relating to that individual exactly matches mine will the
identifier you generate match mine - otherwise, we'd get different, but
still unique, values. If we were both to publish our data, tagged with
that id, we'd be reasonably assured, if the ids were identical, that we
were dealing with the same person and, in point of fact, with identical
information relating to that individual, with whatever consequences that
might suggest.

And that's what I _thought_, maybe better said hoped, the uids/uuids
generated by phpGedView or associated with some records on RootsWeb might
be. Clearly, though, they are not as I had hoped/thought and I'm left
wondering what value, if any, they have beyond being just another label.


Understood that
that's based strictly on the meanings of the words universal and unique.

universal, adjective, modifies unique. Universal does *not* modify
"identifier".
However, if an identifier is universally unique ... Given the conditions
for generating an identifier outlined above, it would be both unique and
universal, in so far that no other similarly generated identifier would
exactly match it - there would be NO collisions, in other words within the
universe of similarly generated identifiers.
<snip>
Now, granting my understanding is deficient, would somebody please define
just what IS meant by the phrase universally unique id? And, if it

It's (universally unique) ID, not (universal ID) and (unique ID).


On my computer, I can get a UUID by typing "uuidgen". It takes no
arguments. It makes no difference whether I intend to attach this
UUID to my father's birth certificate, to my father, to a USENET
news posting, or to one of my socks.

Technically, the UUID is generated from a MAC address of the computer,
a very fine-grained time stamp, a counter, and some other stuff. There
are other procedures to use if the computer doesn't have a MAC address.

See RFC 4122 for a complete description. The uuid you describe is just one
variety - in fact, the first of several. See particularly Para 4.3, which
discusses a uuid generated from an "arbitrary" string.

Fun chatting with you.

Sleepy Ol' Bob

--
Robert G. Melson | Rio Grande MicroSolutions | El Paso, Texas
-----
A government big enough to give you everything you want is big
enough to take away everything you have. Thomas Jefferson
.

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