[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Should information be encoded into identifiers?
Excellent question. I have a few opinions related to vast failures in my past :) I have found that having symbolic identifiers is much preferable to purely numeric (or seemingly random) identifiers. The reasons are both human and programatic. Human reasons If an identifier has human readable meaning then the chance of it being confused is less. This is a big problem with versioning and merging. Suppose you have a catalog system of stuff (say books), and you number then 1,2,3 ... 99934315 ... Then do a backup. Then you add more books ... and delete some. Supose multiple systems are doing this. Then you want to merge 2 datasets, either a backup + current, or 2 peoples datasets. If you use purely numeric system its very hard to tell if "55314" in set 1 is the "same thing" as "55314" in set 2. Wheras if you have "Joes_Random_Amusements" and "Joes_Random_Amusements" from 2 different sets, the chances of them being "the same thing" is much higher. Why ? From a computer perspective in both caes the string is an exact match, but from a human perspective if the ID has some meaning in it, its easier to tell if it's the same thing. This leads me to belive that whenever possible ID's should both be strings, and have meaning. Programmatic Reasons Similar to human reasons. If you encode meaning into an ID, it is ideal if the generation of that ID is reproducible without state. That is, without a central catalog dishing out ID's. Take your ISDN numbers ( or MAC addresses). Because they segment the ID into company portions, its possible for each company to assign meaning to the ID's ... and ideally if they have to re-generate an ID from 'the same thing' it should produce the same ID. This is not always possible but it is a goal. If you can possibly generate an ID reproducibly from the object that is an ideal case. If not, then if you can generate an ID that a human can recognize as likely representing that object that is good. There's other reasons too ... but I'll stop while I'm behind. ---------------------------------------------------- David A. Lee dlee@calldei.com http://www.calldei.com http://www.xmlsh.org -------------------------------------------------- From: "Costello, Roger L." <costello@mitre.org> Sent: Friday, March 05, 2010 4:57 PM To: <xml-dev@lists.xml.org> Subject: Should information be encoded into identifiers? > Hi Folks, > > Should identifiers be dumb? That is, no meaning can be ascribed to > identifiers; they are completely random. > > Or, should information be encoded into identifiers? What information > should be encoded into them? > > There are precedents for encoding information into identifiers: > > 1. In the U.S. each auto is identified by a Vehicle Identification Number > (VIN). Encoded within each VIN is a wealth of information, including the > make and model of the auto, the plant where it was manufactured, and the > vehicle's options.[1] > > 2. Books are identified by ISBNs. Encoded within each ISBN is a wealth of > information, including the country, publisher, and the relative size of > the publisher.[2] > > 3. UUIDs are used in many applications. Encoded within some UUIDs are the > date/time stamp of when the UUID was created, and the network address of > the machine which created the UUID.[3] > > I suspect there are other examples of identifiers that have information > encoded into them. > > What are the advantages of encoding information into an identifier? What > are the disadvantages? > > /Roger > > [1] Format of VIN: http://en.wikipedia.org/wiki/VIN > > [2] Format of ISBN: http://www.xfront.com/isbn.xsd > > [3] Fomat of UUID: http://www.ietf.org/rfc/rfc4122.txt > _______________________________________________________________________ > > XML-DEV is a publicly archived, unmoderated list hosted by OASIS > to support XML implementation and development. To minimize > spam in the archives, you must subscribe before posting. > > [Un]Subscribe/change address: http://www.oasis-open.org/mlmanage/ > Or unsubscribe: xml-dev-unsubscribe@lists.xml.org > subscribe: xml-dev-subscribe@lists.xml.org > List archive: http://lists.xml.org/archives/xml-dev/ > List Guidelines: http://www.oasis-open.org/maillists/guidelines.php >
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