XML Information Set Requirements, W3C Note 18-February-1999

Nathan Kurz nate at valleytel.net
Fri Feb 19 21:12:32 GMT 1999

> Clark Evans writes:
> > Constantly viewing XML as a standard for the description 
> > of "data objects" and not "data streams" is a subtle, and 
> > important bias.  It is taking object-orientation too far 
> > and discarding parallel stream processing, and it's related
> > technologies like SAX and SAXON.

Jumping in on Clark's side, there does seem to be a strong bias for
using XML solely as a source for recreating pre-existing "data
objects".  This is a fine use, but seems unnecessarily limiting.

Michael Orr writes:
> For instance, is one aspect of your thinking a desire to chunk an
> "XML stream" so that validation can be performed incrementally,
> while still wishing the XML rec to govern the overall
> well-formedness (?) of the stream as a whole? Or is this totally off
> base? I'm groping to understand the point of view you're promoting
> here...

To me at least, validation isn't that important.  So long as the parts
I choose to parse are well-formed, I don't care if the whole stream is
well-formed.  And if the stream is continuous (for example, an XML
stock ticker) even the concept of a well-formed stream seems tenuous.

Objects seem to carry with them a requirement for full and faithful
representation.  Your first task is always to reconstitute the entire
'document' object to its pre-XML state (ie, parse the entire document
and build a complete object model).  This doesn't need to be the case,
of course, but it seems to be the default.

With a stream, one feels more free to pick and choose, keeping only
the parts that are relevant to the task at hand.  And better, you can
work with those parts as soon as you have them, as there is often no
need to wait for an entire object to be created.  For some reason,
working with a half-parsed object seems wrong.  Working with half a
stream seems perfectly natural.

All semantics, I suppose, but important ones.

Nathan Kurz
nate at valleytel.net

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