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Re: Possibility of an XML Document Type

From: <Noah_Mendelsohn@lotus.com>
Date: Fri, 5 Oct 2001 09:52:05 -0400
To: xml-dist-app@w3.org
Message-ID: <OF219159AC.BD3BEDBA-ON85256ADC.004AF2D7@lotus.com>

Several responses to this proposal have come in.  To save email, I'll
respond to all I've seen here in one mail.  First, thanks to the many who
said this was an interesting direction to explore.

Rich Salz writes:

>> SOAP with attachments would also address this, right?

It's an option, but I think you lose a lot.  You can't process the
attachements as XML.  You can't run them in an obvious way through XSL or
XPath.  They wouldn't obviously get stored in a database with the message.
This option would be for cases where you really want the document in the
message.  There will be a cost, for the bin64 or whatever encoding.

Andrew Layman writes:

>> base64Binary is a format for representing arbitrary data, but hexBinary
is also.  We should be able to embed a complete XML document using either

I agree, and in principle others should be possible too.

>> This suggests that a distinct attribute is needed, perhaps
>> something along the lines of

>>           <abc xsi:type="xsd:base64Binary" xsi:mimeType

Relating it to MIME types seems like a very cool idea, but I'm
uncomfortable taking this out of the type system.   In some ways, the
architecturally ideal way of doing this is unlikely to be practical.  I
think that would be to introduce a new facet into the XSD type system for
the binary types.  It would be a facet that would (optionally) indicate
"mime type of encoded data".  Then you could derive subtypes of both
base64Binary and hexBinary in a clean way.

Even lacking this facet, I think we should declare subtypes.  I think I
really want to be able to do this typing either in the schema or an
instance, and your suggested attribute works only in the instance.  I also
feel its quite important to encode this as a type.  In XPath 2 I presumably
want to say things like "find all nodes that are nested XML documents", in
queries I want to understand this as a return type, etc.  I think this is
type information and we should try to represent it as such.

This seems to be an area where we miss either multiple inheritance and/or
user-defined facets in the XSD type system.  You'd really like to say both
of "this is binary, regardless of encoding, and "this is application/xml",
regardless of bin64, hex, or other encoding.

Thanks to everyone for your encouragement.  I hate to make the spec bigger,
but I think that carrying XML inside of SOAP messages is a good thing to be
able to do.  Indeed, I think it's needed equally in other XML documents.
If so, we should perhaps make the case for the Schema WG to include this in
the type library.  Gudge, what think you?

Noah Mendelsohn                                    Voice: 1-617-693-4036
Lotus Development Corp.                            Fax: 1-617-693-8676
One Rogers Street
Cambridge, MA 02142
Received on Friday, 5 October 2001 10:34:21 UTC

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