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   Behavior and Semantics (was Re: OK, I've read some books, tons of articl

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  • From: Peter Murray-Rust <peter@ursus.demon.co.uk>
  • To: moliphan@footprint.com,xml-dev@ic.ac.uk
  • Date: Thu, 04 Jun 1998 22:31:12

Join the club, Mike - this is a major area of activity.

You have rightly realised that a DTD defines the structure of a document,
but not how it behaves or what should be done with it.

There are two sorts of objects that will be interested in XML documents,
humans and machines (and possibly some combination).

For humans the most common activity will be using a stylesheet to render
the document in a way that is more meaningful to a human. Thus <TITLE>
could be rendered in large font in the middle of the page. Most humans can
recognise a title because they have seen thousands in their life. Similarly
something like
<DATE format="ISO8601">19980604</DATE> might be rendered as
June 4 1998
- the information is no different but it may be better understood

At 17:01 04/06/98 -0400, moliphan@footprint.com wrote:
>A question I have is, how does my behaviour travel with the data (as
>structure does not define behaviour)? I have seen how Java parsers can
>traverse document elements, and given elements I can now associate actions
>with them using Java, but how does that help you, my interested party
>unless you can use my code with the data?

Machines need other ways of interpreting XML data and so - for example - if
I send someone a molecule in XML a stylesheet isn't much help. You have to
have a program. So long as we all agree on the DTD and the semantics and
the ontology (tough) it doesn't matter what program we use.  Unfortunately
much chemical ontology is hardcoded into programs.

>Also, is an XML file going to act as a database in some circumstances?
>Although I have seen examples of this, I wonder how the heck that is
>supposed to work with the portability idea as multiple database instances
>would be difficult to reconcile.

XML will be used to transport data in a variety of 'formats'. Some will map
directly onto well-know structures (e.g. RDBs) but others will be less
structured. I make a lot of use of data in flexible structures and by using
tree navigation can often use the XML document 'as the database'.

>The paradox as I see it is that XML provides an open definition of
>structuring data, but there is difficulty then in providing a generic (low
>cost) method of using the data. My data will be (and, hopefully act)
>different from yours and everybody else's, therefore no generic agent is
>going to know what to do with it.

Your *data* may be different, but hopefully your ontology can be mapped
onto other peoples. Thus maths will use MathML - the equations will vary ,
but they will all use the same DTD. Similarly chemists and biologists can
use CML, and assuming they all mean the same thing by a an ATOM (fairly
easy) and BOND (*not trivial*) they can interchange information seamlessly.
 Moreover mathematical chemists can use both MathML and CML in the same
document using the namespace approach.


Peter Murray-Rust, Director Virtual School of Molecular Sciences, domestic
net connection
VSMS http://www.nottingham.ac.uk/vsms, Virtual Hyperglossary

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