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XML-L  January 2002

XML-L January 2002

Subject:

Re: A schema question from a novice

From:

Wendell Piez <[log in to unmask]>

Reply-To:

General discussion of Extensible Markup Language <[log in to unmask]>

Date:

Fri, 11 Jan 2002 17:34:12 -0500

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (66 lines)

Sue,

At 03:16 PM 1/11/02, you wrote:
>I have recently started learning XML and was going
>through the microsoft tutorial. I was looking at their
>example of a schema xml file which started with the
>following line:
><Schema xmlns="urn:schemas-microsoft-com:xml-data"
>   xmlns:dt="urn:schemas-microsoft-com:datatypes">
>
>The above schema seems to use microsoft specific URNs.

Yes, their literature favors their own schema language.

>Does this mean that the schema XMLs are dependent on
>the XML product we choose i.e if I need to create a
>schema for my XML files where I need to use data
>types, can I write generic schema that works
>- any XML parser
>- and any browser

There are a number of schema languages now available, with support for them
differing between tools. Of those, there are three in particular that you
should know about:

DTD -- a schema language XML inherits from its progenitor, SGML. The only
schema language actually described in the XML Recommendation, and still the
most widely supported. Very standard, quite well understood, but somewhat
limited in its application: DTDs validate XML documents structurally
(element names and structural relations) and provide limited support for
validating other things such as referential integrity; but they don't
validate, for example, data types in document content.

W3C XML Schema -- Standardized last year by W3C, much more fully featured
than DTD; also still somewhat experimental (not fully understood in the
industry), with tool support coming along. W3C XML Schema does include
support for data type validation.

Microsoft XML-Data -- the schema language you've encountered in their
literature. An early pre-emptive strike at an XML Schema language; not
supported by other tools vendors.

There are other schema languages (e.g. RelaxNG coming out of ISO; other
experimental efforts, etc.) but at this point you're probably safe to
concentrate on DTDs and XML Schema, if you need its features; these are
standard and vendor-independent (RelaxNG is also quite promising in this
regard). Microsoft's XML-Data is not.

Look for some other literature to guide you; the MS stuff is best balanced
by other points of view. If you develop with some care to the standards,
XML is very far from being a Microsoft-dependent technology although MS has
appeared guilty, from time to time, of trying to put their brand on it.

I hope that helps!
Wendell


======================================================================
Wendell Piez                            mailto:[log in to unmask]
Mulberry Technologies, Inc.                http://www.mulberrytech.com
17 West Jefferson Street                    Direct Phone: 301/315-9635
Suite 207                                          Phone: 301/315-9631
Rockville, MD  20850                                 Fax: 301/315-8285
----------------------------------------------------------------------
   Mulberry Technologies: A Consultancy Specializing in SGML and XML
======================================================================

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