Re: [boost] Proposal: XML APIs in boost

From: Graham Bennett (graham-boost_at_[hidden])
Date: 2005-11-10 20:28:54

By the way, do you think there is any merit to the idea of introducing
policies for the way the DOM is created/stored?

Graham.

On Wed, Nov 09, 2005 at 09:21:45PM -0500, Stefan Seefeld wrote:
> Graham Bennett wrote:
> > Hi Doug,
> > 
> > On Tue, Nov 08, 2005 at 09:28:09PM -0500, Douglas Gregor wrote:
> 
> >>Readers are important for some things, DOM is important for other
> >>things, but there's no reason to tie the two together in one library
> >>or predicate one on the other. 
> > 
> > 
> > Well, there is at least one reason - if the DOM is built on top of a
> > reader interface then the DOM library doesn't have to know how to parse
> > XML, and is not tied to any particular parser.  Even if you don't agree
> > with using a reader interface for this separation layer, I'd hope you
> > would agree that some separation is at least necessary.
> 
> I wish people would stop being so parser-focussed. I reiterate:
> the API I suggest is about manipulating a DOM tree. The fact that
> you *might* want to construct it from an XML file by means of a parser
> is almost coincidental.
> 
> Yes indeed, an implementation of such an XML parser will most likely
> use either a SAX or an XmlReader layer beneath, and in fact, libxml2
> does exactly that and it would be quite natural to expose those APIs
> to C++ in a similar way I propose the DOM wrapper.
> 
> >>We can have a XML DOM library that  allows reading, traversing,
> >>modifying, and writing XML documents,  then later turn the reading
> >>part into a full-fledged streaming  interface for those applications.
> > 
> > 
> > Can you elaborate on how you would enable a DOM structure to present a
> > streaming interface?
> 
> Not the DOM structure, but the parser ! It's exactly what you are saying
> above: Each sensible XML parser will use an API underneath that can be
> used to build a public SAX or XmlReader (or both) on top of.
> 
> But instead of requiring the parser to be built on such a C++ API I
> use a C implenentation that already contains multiple APIs, and I wrap
> them *separately* into C++ APIs. For a user of the C++ DOM API it is
> totally irrelevant whether the implementation is based on the C++ SAX API
> or an internal C SAX API, as long as it adhers to the specification.
> 
> 
> > Are you talking about lazy tree building or
> > something else?  In any case, I would think it's inherantly difficult to
> > retrofit a streaming interface.  Much better to build the streaming
> > interface from the start, and build the DOM on top of it.  This can only
> > be good for both sides - the reader gets to just be a reader, and the
> > DOM gets to just be a DOM.
> 
> You haven't talked about the DOM yet, only about a parser. You still
> need to provide all the other missing bits, such as an XPath lookup
> mechanism, XInclude processing, http support for URI lookup, etc., etc.
> I can't stress it enough: the parser is really just a tiny bit of it all.
> 
> Regards,
> 		Stefan
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Graham

-- 
Graham Bennett