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RE: Re: Syntax + object model

• To: "Murali Mani" <mani@C...>,<xml-dev@l...>
• Subject: RE: Re: Syntax + object model
• From: "Dare Obasanjo" <dareo@m...>
• Date: Sat, 24 May 2003 10:40:10 -0700
• Thread-index: AcMiGiPCJhZYJsDeT8+Bu230DcuymAAADMYd
• Thread-topic: Re: Syntax + object model

a.) The data model is a foundation upon which application semantics can be built. I can say similar things about how the relational model's quaint notions of tuples and  keys does not make it easy to answer questions like "Who is my best customer?". However this doesn't mean I can't create databases that hold my customer information nor can I create queries that answer such questions. Similarly, it doesn't mean once I have done this my application semantics will directly expose the underlying structure of my database or the underlying SQL queries being run. 
 
b.) Since XML Schema documents are constructed as XML as long as I have all the input schemas accessible as documents I can construct queries in XQuery that can retrieve information like "find all 
possible element tags that could be descendants of an element" actually I'm sure you meant to say find all elements whose type definition is a descendent of the type definition of another element since XPath provides a trivial way to get the descendants of an element.  

________________________________

From: Murali Mani [mailto:mani@C...]
Sent: Sat 5/24/2003 10:29 AM
To: xml-dev@l...
Subject: RE: Re:  Syntax + object model




Because I am working on data models, I will share my two cents worth of
impressions..

First off, data model consists of 3 parts: structures, constraints, and
operations.

You can standardize such data models only for applications.

The XQuery/XPath data model is for applications that want to retrieve data
from XML documents. The operations are defined using XPath/XQuery.

But this does not make it a standard for all applications, we can write
xml schemas also as XML. Do the same model and operations as defined in
XPath/XQuery suitable? probably not..

It probably is not useful to define, for example, what are the children of
a complex type? it could be xsd:sequence.. what do you get from it?

Similarly, suppose you want to write a query like: I want to find all
possible element tags that could be descendants of an element? It is
definitely not easy to write such a query using XPath..

So when you want to analyze XML Schemas, you want to probably come up with
a different data model, and probably a different set of operations..

Conclusion: I believe it is not right to say XPath/XQuery data model is
*the* data model for all XML documents..

cheers and regards - murali.


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