RE: [xml-dev] Should information be encoded into identifiers?

["Jim Tivy" <jimt@bluestream.com>]

Hi Folks

Here is a slightly different twist on use of local identifiers within a
system.
We had to decide this when assigning IDs in our CMS.  In the end we went
with an ID that had no semantic information with an "annotation" added to
the ID.  The reason we added the annotation is if you encounter a link in
the XML to, for instance, an image, you might want to know something
semantically about the linkee being referenced in some far flung "raw" XML
editor (unlike a WYSIWYG XML Editor) - like Oxygen in raw mode or a Browser
XML view.

For example:

href="/Content/foo_xi46.gif" references foo_xi46.gif somewhere in the CMS.
The "/Content/foo_ " and the ".gif" are only annotations.  The "xi46" is the
unique identifier.

Since they are annotations, if you change the name of the file (or less
often the file extension) then the link does not break and we can fix up the
link next time we touch that file.

Now, in a closed system such as this, you might argue that you just need
hover text and properties and then there is no need for these annotations -
but our system is not closed with people able to use outside tools to
inspect the raw XML - thus we ended up with these identifer annotations.

Jim

-----Original Message-----
From: Costello, Roger L. [mailto:costello@mitre.org] 
Sent: Friday, March 05, 2010 1:58 PM
To: xml-dev@lists.xml.org
Subject: [xml-dev] 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
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