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Re: Local element symbol space breaks with XML 1.0?

From: <Noah_Mendelsohn@lotus.com>
Date: Tue, 7 Mar 2000 22:03:12 -0500
To: David Skogan <dskogan@cs.keele.ac.uk>
Cc: www-xml-schema-comments@w3.org
Message-ID: <OF19374666.20526855-ON8525689B.0052159B@lotus.com>
>> But if I understand it correctly it may break with XML 1.0, 
>> which states that "No element type may be declared more than once." 

A DTD, which is what XML 1.0 discusses, can declare an element of a given 
name at most once.  Schemas is free to invent its own notions of 
definition.  Note that the following is well formed XML 1.0:

        <DOC>
                <PERSON>
                        <TITLE>Ms.</TITLE>
                        <NAME>Mary Jones</NAME>
                </PERSON>
                <BOOK>
                        <TITLE>War and Peace</TITLE>
                        <AUTHOR>
                                <TITLE>Ms.</TITLE>
                                <NAME>Leo Tolstoy</NAME>
                        </AUTHOR>
                </BOOK>
        </DOC>

Schemas lets you do what DTD's do not:  make the titles and names locally 
scoped, and perhaps to have the person titles defined as an enumeration 
(Mr., Ms., etc.)

------------------------------------------------------------------------
Noah Mendelsohn                                    Voice: 1-617-693-4036
Lotus Development Corp.                            Fax: 1-617-693-8676
One Rogers Street
Cambridge, MA 02142
------------------------------------------------------------------------







David Skogan <dskogan@cs.keele.ac.uk>
Sent by: www-xml-schema-comments-request@w3.org
03/03/00 05:50 PM

 
        To:     www-xml-schema-comments@w3.org
        cc:     (bcc: Noah Mendelsohn/CAM/Lotus)
        Subject:        Local element symbol space breaks with XML 1.0?

I personally think the local symbol space for types is a very good
thing. It allows local content elements to have local names, and solves
some of the global name space problems. Quote from 2.5:

"Attributes and local element declarations are special, in that every
type defines its own attribute symbol space and local element symbol
space, which are distinct from each other. In addition, top-level
elements (whose declarations are not contained within a   type
definition) reside in their own symbol space. "

But if I understand it correctly it may break with XML 1.0, which states
that "No element type may be declared more than once." I interpret the
local symbol space of a type to mean that I can define a type "T1" with
an element "E1" and then go on defining another type with the same
element name "E1" but with another type. Something like this:
 
<type name="T1">
                 <element name="E1" type="integer"/>
</type>

<type name="T2">
                 <element name="E1" type="T1"/>
</type>

<element name="T1" type="T1"/>
<element name="T2" type="T2"/>

XML instances based on this schema may look like:

<T1><E1>1324</E1></T1>
<T2><E1><E1>42</E1></E1></T2>

Here we have two "E1" elements that have different type, and this
probably willlead to ambiguities. Is this the intention and will it mean
that you break with XML 1.0? I'm quite happy with having it this way,
this means that you can reuse element names and in effect get a local
name space for each element.

Please clarify this, thanks.

David Skogan

-- 
David Skogan
Visiting PhD student,
Computer Science Dep., Keele University, Staffordshire, ST5 5BG, United
Kingdom
dskogan@cs.keele.ac.uk, http://www.ifi.uio.no/~davids/
(phone) +44 1782 584270
Received on Tuesday, 7 March 2000 22:05:24 GMT

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