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   Re: Access Languages are Tied to Schemas

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  • From: Joe Lapp <jlapp@acm.org>
  • To: xml-dev@ic.ac.uk
  • Date: Thu, 20 Nov 1997 11:52:19 -0500

"Lauren Wood" <lauren@sqwest.bc.ca> wrote:
>I think it is possible to build a general API for XML documents, so 
>if one of your imposed requirements on a repository is that it be in 
>XML, and a general solution would not require that, then I agree. I 
>do not agree that an object model must be developed for each industry 
>- if the access method is standard, then whichever underlying model 
>of the information a given tool uses doesn't really matter. It will 
>have implications in performance etc, but it should be possible to 
>implement the interfaces if they have been reasonably defined. 

>From reading Jonathan's and Lauren's responses, it looks like I need
to throw in a quick clarification.  I agree that a repository need not
have any knowledge of the semantics of a particular industry.  We
could use a general SGML repository to store any kind of document,
where the repository's only knowledge of the document is its DTD.  
Relational databases (for example) give us this sort of approach, since
they need not understand what is meant by the schemas that are stored
within them.  Elements are the informational units of an SGML/XML
repository in the same way that tables and columns and rows are the
informational units of relational databases.

However, each domain does have information units that are specific to
that domain, and they exist as units regardless of the more fundamental
units from which they are constructed.  An RDBMS's schema specifies
these domain-specific units, as does an XML-document's DTD.  Hence, the
DTD does intend to capture the object-model of a particular domain,
even if this object model is expressed in the language of a more general
object model.  I'm asking a question about what we expect our DTD
schemas to accomplish for these domain-specific object models.  Do we
expect general SGML/XML repositories to be powerful enough to allow
them to represent almost any domain-specific object model?

BTW, I agree that IDL interfaces are another kind of access language to
a repository and that DOM in particular satisfies the property of
access languages I was arguing for.  It provides fundamental contructs
from which domain-specific information units can be built.
Joe Lapp (Java Apps Developer/Consultant)
Unite for Java! - http://www.javalobby.org

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