Behavior and Semantics
peter at ursus.demon.co.uk
Fri Jun 5 08:12:02 BST 1998
[from David Durand]
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> Date: Thu, 4 Jun 1998 21:10:05 -0700
> From: david at dynamicdiagrams.com (David G. Durand)
> Message-Id: <199806050410.VAA08243 at dynamicdiagrams.com>
> To: xml-dev at ic.ac.uk
> Subject: Re: Behavior and Semantics (was Re: OK, I've read some books, tons
> of articles, and...)
> >From: Peter Murray-Rust <peter at ursus.demon.co.uk>
> >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.
> This is exactly correct. This is because the set of possible behaviors
> a document might exhibit and processes to which it might be subjected
> is an open (infinite) set. By providing names in some well-known
> ontology, we hope to make it easier to re-use information with
> different processes.
> I'm responding to this, because I hope that I can help unconfuse soem
> issues that you have persistently confused as to the applicability of
> the "stylesheet notion".
> >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 at 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.
> This is the point on which you are incorrect. The term stylesheet is
> perhaps confusing, since it implies a formatting specification, but
> then the notion, like most of the notions in XML, comes from the print
> (and online) publishing world.
> XML stylesheets will have a hook to a fully general scripting
> language. That means that it will be possible to have stylesheets that
> access special browser caspabilities, Java code, or whatever. It's
> important that this be done via style sheets, since that's the
> standard mechanism, and since users will be able to change stylesheets
> if they need to interpret the data differently. For instance, you
> might supply a molecule with a "display 3D model" style, while I want
> to "view" it by using my molecular synthesis generation software.
> Both of us are accomodated by XML, and both are served by the use of
> a single method of attaching processing semantics to a document.
> >>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.
> And, using the stylesheet mechanism, you can inform users of the
> method of processing _you_ intend to use with the data.
> In most browsing contexts, a default display stylesheet will be
> appropriate, but the fact XML inherently supports indirection for
> processing methods allows a lot of power for repurposing and upgrading
> data that is already created.
> -- David
> David Durand dgd at cs.bu.edu| david at dynamicDiagrams.com
> Boston University Computer Science | Dynamic Diagrams
> http://www.cs.bu.edu/students/grads/dgd/ | http://dynamicDiagrams.com/
> | MAPA: mapping for the WWW
Peter Murray-Rust, Director Virtual School of Molecular Sciences, domestic
VSMS http://www.nottingham.ac.uk/vsms, Virtual Hyperglossary
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