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From Donald Ball <ba...@webslingerZ.com>
Subject RE: XML Inheritance Extentions (first try)
Date Mon, 20 Dec 1999 04:31:06 GMT
On Sun, 19 Dec 1999, Box, Don wrote:

> I am not sure what this proposal buys that using the 'default', 'source' and
> 'restrictions' facilities of W3C XML schemas couldn't achieve (see
> http://www.w3.org/TR/xmlschema-1/ and http://www.w3.org/TR/xmlschema-2/)? In
> XML Schemas, one can set up not only a 'type' definition, but also its
> initial values. The 'source' attribute allows one to establish type
> relationships via inheritance. The 'restrictions' element allows you to
> alter the requirements of a type by constraining the values used in derived
> types.

A few problsm I can think of right offhand:

1. The author has to write a Schema instead of just adding some elements.

2. Can you do polymorphism?

3. Can you do extended inheritance (e.g. inherit attributes from a logical
parent's logical parent?)

Of the 3, I think the 1st point is possibly most salient. What I'm trying
to use this for is configuring an XML->SQL->XML application. My
configuration elements look like this:

<sql:query
 driver="org.gjt.mm.mysql.Driver"
 dburl="jdbc:mysql://mysql.example.com/test"
 username="test"
 password="test"
>
 select * from foo_table
</sql:query>

(there are, of course, many more attributes possible in the sql:query
element, but this illustrates the idea). Anyway, I want to write down the
connection information in one place and refer to it from all of the
various query nodes in all of my various documents. Is it appropriate for
me to ask users to write a new schema for each site? Plus, suppose the
user wants to use two seperate database connections in their XML files and
want their sql:query elements to refer to one or the other. Using
Stefano's syntax, this is possible, but not so with schemas, at least as
far as I understand your example.

- donald


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