RE: [xml-dev] 'is-a' Relationships in XML?

["Michael Sokolov" <sokolov@ifactory.com>]

One thing we often do is to attach type information to our xml documents
using a <dc:type> element, which tells us that a given document "is a" book,
chapter, section, appendix, etc.  This is useful when dealing with a variety
of different XML schemas that don't share a common vocabulary for the things
that we want to treat similarly.   It works by providing a hook into an
external type system which has inheritance and so on, and is useful, but it
doesn't really have much to do with XML directly.  Some evidence, I guess,
that you need to go outside the document to express "is-a" relations.

-Mike

> -----Original Message-----
> From: stephengreenubl@gmail.com [mailto:stephengreenubl@gmail.com] 
> Sent: Monday, May 03, 2010 7:47 PM
> To: Michael Kay; stephengreenubl@gmail.com
> Cc: 'xml-dev'
> Subject: RE: [xml-dev] 'is-a' Relationships in XML?
> 
> But back to my initial question and the responses, it seems 
> safe to conclude that while semantics should be explicitly 
> defined somewhere other than the markup alone or XSD, etc, 
> any implicit semantics are easier to see in the markup when 
> they concern 'hasA' relationships of belonging but not so 
> clear when they involve 'isA' relationships of inheritance or 
> equivalence because these can only really be represented 
> using a schema like XSD. This seems peculiar to XML. So this 
> seems another reason to separately define the semantics 
> formally of any markup and not to leave it just to what is 
> implicit in the structure and node names.
> 
> Stephen D Green
> 
> 
> 
> -----Original Message-----
> From: stephengreenubl@gmail.com
> Sent:  04/05/2010 12:32:03 am
> To: Michael Kay; stephengreenubl@gmail.com
> Cc: 'xml-dev'
> Subject:  RE: [xml-dev] 'is-a' Relationships in XML?
> 
> But clearly the markup can need more explanation via semantic 
> definitions or specifications than would be needed by 
> straight prose statements. E.g. I can lie by stating that I 
> own Buckingham Palace. That implies Stephen D Green owns 
> Buckingham Palace and this is not true. If I write markup 
> <place name='Buckingham Palace'><owner>Stephen D 
> Green</owner>then it depends what 'owner' means as to the 
> truth and meaning of the markup. It could be the same lie as 
> above or it could be the start of a document about a place 
> where I was owner of the document, not owner of the place. So 
> yes I accept to some extent what folk here are saying but 
> with some reservation, as I think would anyone since we 
> always leave some understanding of the semantics to the 
> markup itself and don't express all of it in the spec and 
> related defining artefacts. Plus we tend to let the schema 
> express some semantics, as I was advised in early responses 
> here, without perhaps restating all such semantics in a spec. 
> We understand though the dangers and risks and address the 
> clearest risks by making some semantics like calculation 
> models explicit in a spec, perhaps even using formal logical 
> english or a calculus. Or we create other artefacts 
> specialised for expressing semantics like topic maps or 
> ontologies and take it, in doing so, that the markup and 
> maybe XSD do not adequately cover semantics but rather are 
> optimised to express structure and constraints on structure. 
> That makes sense.
> Thanks
> Steve
> Stephen D Green
> 
> 
> -----Original Message-----
> From: stephengreenubl@gmail.com; stephengreenubl@gmail.com
> Sent:  03/05/2010 11:49:25 pm
> To: Michael Kay
> Cc: 'xml-dev'
> Subject:  RE: [xml-dev] 'is-a' Relationships in XML?
> 
> 
> 
> 
> -----Original Message----
> From: Michael Kay
> Sent:  03/05/2010 11:35:35 pm
> To: stephengreenubl@gmail.com
> Cc: 'xml-dev'
> Subject:  RE: [xml-dev] 'is-a' Relationships in XML?
> 
> > So making an 'employee' element  a child of an 'employer' 
> > element clearly implies some semantics that the employer 'has' the 
> > employees.
> 
> And if 'employer' is a child of 'employee' then I suppose 
> that the employee "has" the employer. But I don't think 
> there's any semantics here: you're just using "has" as a 
> synonym for "is the parent node of". 
> 
> 
> -sdg:
> Not really. I think I'd be understanding that the markup was 
> using the parent/child to represent the reality of the 'has' 
> relationship. I accept that it's implicit to some extent but 
> even the names of the elememts could be said to imply 
> something about the reality being represented. Just as words 
> represent reality, to some extent implicitly.
> 
> 
> 
> If XML is well designed, then you can make guesses about the 
> meaning of the data from the choice of element names and 
> their hierarchic relationships.
> But XML is often badly designed, and your guesses in such 
> cases will be wrong.
> 
> Regards,
> 
> Michael Kay
> http://www.saxonica.com/
> http://twitter.com/michaelhkay 
> 
> 
> 
> 
> 
> 
> 
> 
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