Object-oriented serialization (Was Re: Some questions)

[Colas Nahaboo]

Matthew Gertner writes:
> The aspects of
> object-oriented design that are missing are then inheritance and
> polymorphism. 

In my opinion, things may be more simple. If SGML/XML had not been designed by
people living in a typeless world (text documents), XML could have provided a
much better medium to express object instances, with such a simple design as
getting rid of element contents, and allowing attributes contents to be XML,
e.g:

<Point
  x=<Length unit="inches" value="12"/>
  y=<Length unit="cm" value="2"/>
  color=<RGB R=<Number base="16" value="FF"/> G="0" B="0"/>
/>

matching a C/C++/Java... declaration of Point as:

Point {
  Length x;
  Length y;
  Color color;
};

As you can see, this would be a very elegant and natural way to express object
instances (aka serialization). One would of course need a schema language on
top of that (to express what I wrote in a C-like declaration), but having to tweak the "low-level" serialisation to fit in the
current XML1.0 recomendation is I think the original sin of XML, which
pollutes a lot of the discussions I see here. For instance the current drive
for removing attributes results from this.
 
But, just like RDF, we could standardise on this non-XML-1.0-compatible (lets
call it GXML for Generalized XML :-) representation, and devise a canonical
way to express it in XML.  For instance:

<Point>
  <_x><Length unit="inches" value="12"/></_x>
  <_y><Length unit="cm" value="2"/></_y>
  <_color><RGB G="0" B="0">
       <_R><Number base="16" value="FF"/></_R>
  </_color>
</Point>

but we could devise others...

--
Colas Nahaboo, Koala/Dyade/Bull @ INRIA Sophia, http://www.inria.fr/koala/colas


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