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RE: Subtyping in XML


mythical man months
Many of the OO luminaries use encapsulation interchangeably with information hiding or link them closely. From the article you linked to I quote 
 
"
*	Cox'definition allows for encapsulation to reveal some information, for example full visibility to the procedures offered by object, while hiding some other information, for example no visibility to data. 
*	Booch and Rambaugh make no distinction between information hiding and encapsulation. "
 
I'll take the opinions of Brad Cox and Grady Booch over anyone who uses public member variables,  C++ or arrays to argue points about OO. No offense to Berard, intended. 
 
The truth about software engineering is that most of the core tennets around it are based on opinions, conjectures and best practices. Moore's law, Mythical Man months and Extreme Programming are all just theories and opinions. Some opinions believe information hiding is akin to encapsulation while others believe it is merely grouping things together. The former makes sense to me with regards to what I believe is effective object oriented programming while the latter does not. 
 
Anyway this is rather offtopic for XML-DEV so email me offlist if you want to continue this discussion. 
 

	-----Original Message----- 
	From: Maciejewski, Thomas [mailto:Thomas.Maciejewski@l...] 
	Sent: Tue 9/10/2002 11:12 AM 
	To: Dare Obasanjo; Maciejewski, Thomas; Henry S. Thompson; Jeff Lowery 
	Cc: paul@p...; Xml-Dev (E-mail) 
	Subject: RE:  Subtyping in XML
	
	

	I grabbed this snippet from:http://www.arcc.or.ke/ken_it1.htm
	and although the definition of encapsulation is closely linked to
	information hiding I am not sure if your argument that XML does not provide
	information hiding eliminates it entirely from being used in combination of
	the term OO.  In any case here is a statement that at least throws a bit a
	vagueness on the definition of encapsulation:
	<quote>
	According to Berard [Ber93], if encapsulation were the same as information
	hiding, then one would argue that everything that was encapsulated was also
	hidden. This is not true. For example, even though information may be
	encapsulated within arrays the information is not hidden. Another example is
	the creation os some global data in C++ class public interface, the data is
	not hidden.
	</quote>
	
	so although XML doesn't hide data it seems that it can encapsulate and
	promote the reuse of object like elements ???? 
	
	
	
	
	-----Original Message-----
	From: Dare Obasanjo [mailto:dareo@m...]
	Sent: Tuesday, September 10, 2002 1:48 PM
	To: Maciejewski, Thomas; Henry S. Thompson; Jeff Lowery
	Cc: paul@p...; Xml-Dev (E-mail)
	Subject: RE:  Subtyping in XML
	
	
	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@l...]
	        Sent: Tue 9/10/2002 10:37 AM
	        To: Dare Obasanjo; Henry S. Thompson; Jeff Lowery
	        Cc: paul@p...; Xml-Dev (E-mail)
	        Subject: RE:  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@m...]
	        Sent: Tuesday, September 10, 2002 1:20 PM
	        To: Henry S. Thompson; Jeff Lowery
	        Cc: paul@p...; Xml-Dev (E-mail)
	        Subject: RE:  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
	        language".
	       
	        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@c...]
	                Sent: Tue 9/10/2002 10:08 AM
	                To: Jeff Lowery
	                Cc: 'paul@p...'; Xml-Dev (E-mail); Dare Obasanjo
	                Subject: Re:  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
	        in
	                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
	        so
	                far as C++ took a number of OO design patterns generally
	        acknowledged
	                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
	        the
	                tag-type distinction, derivation by restriction and
	extension, named
	                element and attribute groups and substitution groups, the WG
	was
	        very
	                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
	                lib._).
	              
	                ht
	                --
	                  Henry S. Thompson, HCRC Language Technology Group,
	University of
	        Edinburgh
	                          W3C Fellow 1999--2002, part-time member of W3C
	Team
	                     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44)
	131
	        650-4440
	                            Fax: (44) 131 650-4587, e-mail:
	ht@c...
	                                     URL: http://www.ltg.ed.ac.uk/~ht/
	                 [mail really from me _always_ has this .sig -- mail without
	it is
	        forged spam]
	              
	       
	       
	       
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