GUID Guide, part one

re: GUID Guide, part one

efflux — Fri, 11 May 2012 21:59:22 GMT

(*) The attentive reader will note that there are usually two bar codes on a book in the United States. The first one is the ISBN; the second bar code is the number 5 followed by a four digit number that is the publisher's suggested price of the book in American pennies.

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In another incarnation back when I was in univeristy, I worked at the university's bookstore and I remember there being two pricing schemes publishers used. One was "list price" where there would a suggested retail price for the book and a set discount passed to the store which was often upwards of 40%. With this pricing, the second barcode would indeed reflect the suggested retail price. The second pricing was "net" pricing, which did not carry a suggested retail price at all. These tended to either be all zeroes or have a number beginning with "9" and seeming random information. Having just read this post prompted me to finally look this up and I see that prefix indicates "internal use". Nice to have that mystery solved :-)

For what it's worth, the "net" priced books tended to be "textbooks" whereas list priced books typically fell under the "trade book" category, which while sometimes required reading for courses were of the type to also be in general circulation.

re: GUID Guide, part one

Jimi — Wed, 02 May 2012 22:39:11 GMT

So GUIDs are created by gnomes are they? Well that will explain all those tiny footprints around our database server.

re: GUID Guide, part one

Static Shock — Wed, 02 May 2012 16:46:34 GMT

I'm very worried that at the rate we are using them we will run out of GUID's and everything after that will have to be non-unique ;-) :-D

re: GUID Guide, part one

Jürg Steffen — Wed, 02 May 2012 07:14:19 GMT

What about the CDDB (http://freedb.freedb.org). I think they have also thought that the indentifier of a Music CD should be unique. But I found also collisions there!

But anyway, good article!

re: GUID Guide, part one

Birthday paradox — Mon, 30 Apr 2012 05:16:30 GMT

I had a colleague who was concerned about GUID collisions, which prompted me to write this explanation:

ralphbecket.blogspot.com.au/.../birthday-paradox-and-guid-collisions.html

The punchline is that you can assign about a million billion GUIDs *before* you hit a one in a billion chance of a collision.

re: GUID Guide, part one

carlos — Sat, 28 Apr 2012 12:40:08 GMT

@Gabe: I was in the USA a couple of weeks ago and, unfamiliar with the coins, grumbled to my brother that the dime must be the only coin in the world that doesn't state how much it's worth (i.e. ten cents).

I didn't realise it was a currency unit, but now I do. Cheers!

re: GUID Guide, part one

Gabe — Sat, 28 Apr 2012 03:26:54 GMT

Phoog: Actually, the American currency system was designed with four units: dollars, dismes, cents, and milles, according to the Coinage Act of 1792. Note that the 's' was soon dropped from 'disme'. No "disme" coin was ever minted, but there was a "half disme" for a while. The first 10-cent coins had no denomination printed on them (they were silver and silver coins were not required to show their denomination), and later ones had the denomination printed as "one dime".

I don't believe any coin was ever minted in milles, and in fact the only place the denomination is commonly used is for taxes. There was a 5 mil coin, but its denomination was "half cent".

re: GUID Guide, part one

Phoog — Fri, 27 Apr 2012 15:30:49 GMT

I note that the name of the US currency subdivision is "cent", not "penny". The name "penny" is commonly used for the coin, but its proper name is "cent". Interestingly, the American currency system was designed with three units, by analogy with pounds, shillings, and pence; these units are dollars, dimes, and cents. This distinction lived on for some time, at least theoretically: I've seen an invoice form from the 19th century with columns for dollars, dimes, and cents. This also explains why the US dime says "one dime" rather than "ten cents".

re: GUID Guide, part one

GUID wasting on a massive scale. — Fri, 27 Apr 2012 13:28:24 GMT

If you want a random record from an SQL Server table, you need to use TOP 1 and ORDER BY NEWID(). (RAND returns the same value for each record in the select.) Does this mean I generate and waste thousands of GUIDs every time? There's only a finite number of them available.

re: GUID Guide, part one

CodeInChaos — Fri, 27 Apr 2012 10:43:54 GMT

You also forgot to mention that `Guid.NewGuid` is the finest cryptographic random number generator available in .net :P