Musing over Namespaces

Len Bullard cbullard at
Sun Dec 19 17:40:50 GMT 1999

Arjun Ray wrote:
> On Sat, 18 Dec 1999, Len Bullard wrote:
> > Dan Brickley wrote:
> >
> > > By defining schema languages in instance syntax, we implicitly
> > > promote the idea that there will be some big payoff for doing so
> > > (otherwise, lets stick with DTDs).
> How about improving DTDs? (Just a thought.)

I guess it could be done but it seems to me this should come 
from the ISO WG responsible for SGML.  However, the issue 
of having to have separate facilities for DTDs is still there 
and being able to use the document framework to get values 
from the schema is useful.  IOW, as I note below, they have 
to be equally powerful in what they express and enable.

 > > There is some payoff:
> >
> > 1.  Political.  XML can finally dissolve the XML to SGML parentage.
> Done deal already: XML is a W3C trademark, and AFAICT, the XML 1.0
> Recommendation does not reference SGML (ISO8879+TCs) normatively.
Spilt milk.  Wish it weren't.

> > 2.  Technically.  It is a stronger schema model.

> Unfortunately, it's now politically correct to break out the garlic and
> crosses at any mention of HyTime - saves having to ask how much of it is
> being reinvented.

For sure, but hey, some of us know who did what when and which names 
go on what inventions.  When someone raises that garlic and cross I 
have to laugh.  Superstition and hero worship... so much for scholarship 
and sound technical judgement.  Let it go.  The point is, they haven't 
delivered on their promises and human memory is not as short as 
Internet time.

> Not there as a "primitive": but it seems possible to have a user-defined
> type with list-like characteristics using "facets".  The data-typing in
> XSchema seems heavily influenced by (R)DBMS-think.

Yes.  It has been noted elsewhere which is why the suggestion that we 
may want to do some things differently in VRML has come up from Sony. 
They suggest we recast PROTOs as VRML schemas.  There is merit to 
the suggestion.  Having done a lot of relational work the last three 
years, I can see where that direction makes sense to RDBMS thinkers.  
To those doing object models, it is a bit less sensible.

> Isn't *some* (form of) schema indispensible?  The real issue seems to be
> the content of schemas (i.e. what they provide for in the way of asserted
> and verifiable constraints) rather than the syntax, although sheer
> clumsiness of instance-syntax could become an issue too.

I agree on both points.  I can live with the clumsiness of the instance 
syntax to enjoy the benefits of the DOM and event-oriented parsers, but 
extensibility was the promise of XML and that is what has to be there
it to be useful.  If that is clumsy, we have a bigger problem.  Again, 
think Record of Authority.  Is it the schema or the runtime engine?

> I'd prefer a useful syntax to a convenient one, where convenience is seen
> through the prism of tools at hand.  Not everything need have to be a nail
> just because we have a hammer.

That would suggest that the DTD HAS to be as powerful as the schema. 
that to happen, action from ISO is needed.  

Good to hear from you, Arjun!


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