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   RE: [xml-dev] Subtyping in XML

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I'm not sure what definition of encapsulation you are using. Encapsulation in OO is the seperation of an object's interface from it's internal data structures and implementation. All XML documents have is internal structure which have to be exposed to do anything with them. 

	-----Original Message----- 
	From: Maciejewski, Thomas [mailto:Thomas.Maciejewski@lehman.com] 
	Sent: Tue 9/10/2002 10:37 AM 
	To: Dare Obasanjo; Henry S. Thompson; Jeff Lowery 
	Cc: paul@prescod.net; Xml-Dev (E-mail) 
	Subject: RE: [xml-dev] Subtyping in XML

	I think this may be because there seems to be a trend towards using XML in
	parallel with OO systems.   ( serializing objects or to help bridge a
	relational data base and an objects )       
	As far as the Inheritance, Encapsulation, polymorphism argument :
	Inheritance - it has it
	Encapsulation - I think at least some elements are there
	polymorphism - I guess your point here is that there is no action so how
	could there be polymorphism ... but since there is a lack of action then
	maybe the polymorphism part of this definition is irrelevant?
	I definitely see XML at least aiding a good OO design ... picture a system
	of xml data that gets passed around a system of "strategy design pattern"
	type code  that excepts this data in and is able to process what is needed
	and pass these "objects" on to something else.
	Doesn't soap also push towards this paradigm?  and why would this not be OO
	or at least a part of the OO paradigm?
	While it may be arguable that XML is NOT OO I wouldn't get too upset when
	you hear OO in combination with XML unless you would like to see XML limited
	to non OO systems.  In my opinion it this would be a major limitation.
	-----Original Message-----
	From: Dare Obasanjo [mailto:dareo@microsoft.com]
	Sent: Tuesday, September 10, 2002 1:20 PM
	To: Henry S. Thompson; Jeff Lowery
	Cc: paul@prescod.net; Xml-Dev (E-mail)
	Subject: RE: [xml-dev] Subtyping in XML
	Every time I read the words Object Oriented or the abbreviation OO in
	combination with XML, I cringe. Objects aren't XML and XML isn't objects.
	W3C XML Schema has some features inspired by OO but I wouldn't go as far as
	calling it OO in XML or even worse calling it an "Object Oriented schema
	The core tennets of OO are encapsulation, inheritance and polymorphism. W3C
	XML Schema gives us 1 of these, once the XQuery REC + F & O are done we'll
	get another. Encapsulation I doubt we'll ever see given the way the current
	family of technologies works.
	This is besides the fact that objects are about behavior not data while XML
	is the exact opposite.
	        -----Original Message-----
	        From: Henry S. Thompson [mailto:ht@cogsci.ed.ac.uk]
	        Sent: Tue 9/10/2002 10:08 AM
	        To: Jeff Lowery
	        Cc: 'paul@prescod.net'; Xml-Dev (E-mail); Dare Obasanjo
	        Subject: Re: [xml-dev] Subtyping in XML
	        > That's a bit of a strawman, IMHO.  It may have been the intent of
	the WG to
	        > produce OO in XML
	        Not produce, but introduce, and I think you're both a little
	        off-target wrt why type definition by restriction and extension are
	        the language.  They're there in large part because the WG had a
	        requirement to improve the managability of the process of syntactic
	        constraint, by introducing 'inheritance' (read OO-design features)
	        into the constraint language.  Think of C --> C++ as a parallel, in
	        far as C++ took a number of OO design patterns generally
	        to be useful for maintaining large programs over time, which C
	        developers had to implement using text-substitution-macros
	        (i.e. #include), and moved them into the language.  In introducing
	        tag-type distinction, derivation by restriction and extension, named
	        element and attribute groups and substitution groups, the WG was
	        consciously trying to do the same thing, looking at existing 'best
	        practise' wrt the use of parameter entities in large DTDs.
	        You may or may not think we got it right, but that was the primary
	        motivation.  The possibility of a better impedence match between
	        documents and application data was a collateral benefit (or not, _ad
	          Henry S. Thompson, HCRC Language Technology Group, University of
	                  W3C Fellow 1999--2002, part-time member of W3C Team
	             2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131
	                    Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
	                             URL: http://www.ltg.ed.ac.uk/~ht/
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