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   Re: XSchema Spec, Sections 2.0 and 2.1 (Draft 1)

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  • From: Chris Maden <crism@oreilly.com>
  • To: xml-dev@ic.ac.uk
  • Date: Mon, 8 Jun 1998 16:47:31 -0400 (EDT)

[Paul Prescod]
> Reuse is important, but it should be more structured than even IDs
> and references. It should be strongly-typed. Something that is an
> attribute type in one context should be an attribute type in all
> contexts. It is the typelessness of parameter entities that causes
> problems. Getting all of the object types right in XSchema 1.0 would
> probably be a bigger project than we need.

But if they're general entities in XSchema, then they get parsed in
context, and their type is enforced by the XSchema DTD.  Picture this:

XSchema with XSchema DTD, before non-DTD entity mechanisms:

<?xml version="1.0"?>
<?xml:namespace ns="http://www.purl.org/NET/xschema" prefix="xsc"?>
<!DOCTYPE xsc:xschema
  SYSTEM "http://www.purl.org/NET/xschema/xschema.dtd" [
<!ENTITY para.content
    <xsc:element idref="emph"/>
    <xsc:element idref="literal"/>
    <xsc:element idref="term"/>
  <xsc:elementdecl id="para">

This is a bit ugly, but it's clean: the type of a "parameter" entity
is validated because it's parsed in context.  Unlike DTD parameter
entities, they have to be declared in the prolog to the schema, but
that makes parsing cleaner.  But then, once there's a non-DTD way to
declare entities:

<?xml version="1.0"?>
<?xml:namespace ns="http://www.purl.org/NET/xschema" prefix="xsc"?>
<?xml:namespace ns="http://www.purl.org/NET/xents" prefix="xent"?>
  <xent:entitydecl id="para.content"><![CDATA[
      <xsc:element idref="emph"/>
      <xsc:element idref="literal"/>
      <xsc:element idref="term"/>
<!-- this is one example of why I think that you shouldn't try to
     tackle entity declarations just yet... -->
    <xsc:elementdecl id="para">

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