xml-dev - Re: RDF Sample, ICAO Airport Codes

[David Megginson <david@megginson.com>]

James Robertson writes:

 > Wouldn't a validatable format with a DTD
 > be more useful for storing data?
 > 
 > ie. plain vanilla XML?

Why not just ASCII?

 > Otherwise, aren't we advocating abandoning XML for a
 > another format? One that loses the ability to be
 > verified, except with the use of custom-written software.

I could write a DTD for my airport example if I wanted, but I see
little value; instead, I'd probably use the W3C's proposed RDF-schema
language, since it works at the right semantic level.

Besides, while DTDs are useful, they allow validation of only a tiny
subset of business rules: as I mentioned in a recent discussion within
the W3C, a DTD can ensure that HTML <h1> doesn't appear within <p>,
but it cannot ensure that the text in it is actually a descriptive
section title.

 > In other words, if RDF is intended for storage of data,
 > what's XML for?

If XML is intended for the representation of documents, what's ASCII
for?

Good application design (like good system design) requires a layered
approach:

- if a lot of people need to extract a stream of characters from many
  different byte encodings, you invent a standard (like Unicode) so
  that they can all refer to a common set of characters in the
  abstract;

- if a lot of people need to extract a tree structure from a
  stream of characters, you invent a standard (like SGML or XML) so
  that they can all use standard software tools rather than rolling
  their own;

- if a lot of people need to relabel the tree nodes with
  universally-identifiable and unique names, you invent a standard
  (like Namespaces in XML or Architectural Forms) so that they can all
  use standard software tools rather than rolling their own;

- if a lot of people need to extract a set of objects from the tree,
  you invent a standard (like RDF or XMI) so that they can all use
  standard software tools rather than rolling their own.


All the best,


David

-- 
David Megginson                 david@megginson.com
           http://www.megginson.com/

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