xml-dev - Re: SAX and whitespace (was Re: Problems with whitespace and msxml)

[Peter Murray-Rust <peter@ursus.demon.co.uk>]

At 21:43 02/01/98 -0500, David Megginson wrote:
>Tim Bray writes:

[...]

> > But I would oppose doing this in SAX; let's keep it simple for now. -T.

I strongly support the word 'simple'.  I also re-emphasise the importance
of SAX.

I have now created a (rather ad hoc) installation of three parsers
(AElfred, Lark, NXP) under JUMBO.  The installation has been in
alphabetical order :-), so most *recent* experience has been gained with
AElfred. To a certain extent I'm waiting for the next releases of the other
two in case they have significant changes. A lot of the work has been
general (how does a GUI interface to a parser) but the following may be
relevant to SAX:

	- is it possible for an author to extend SAX with additional non-SAX
calls? [In the same way as a C library may have the standard calls and some
additional manufacturer-specific ones]. Thus if we agree that doNotation
functionality is not part of SAX, could a core SAX interface be extended by
a parser writer without breaking the SAX bit? [I assume yes, but I don't
know about interface design].

	- if it *is* possible to extend it in this way, can we make sure we get
the core as simple as possible so we all agree on it? Parser writers can
then add additional non-standard functionality [carefully documented, of
course :-)] 

	- there is enormous value for hackers like me to be able to find a simple
core functionality and get that working rapidly. Then the additional
features can be gradually brought in.  

	- what is the position on error handling? In GUI applications like JUMBO
it's important to let the user know what is happening, so I have trapped
the AElfred errors. [I have used a subclass of Error rather than Exception,
because I think that avoids me having to edit and recompile AElfred.] The
information that AElfred reports (URL for entity, line number, textual
description of error (expected/found)) is very useful  and I have built a
little GUI that brings up the document with the errors highlighted (dumbly,
since TextArea doesn't allow me colours). [Note that errorhandling is a
much debated concern in XML and I am NOT suggesting that SAX addresses this
comprehensively or we shall be here for months :-)]. But SAX must report
the error, and I think the entityUrl and the line number and a
(non-standard) message are simple and sufficient at this stage. Whether a
parser stops at the first error is outside our scope at present :-)

I'm looking forward to it - more volunteers (we are NOT limited to Java, if
you can work from GavinN's IDL) would be very welcome.


	P.

Peter Murray-Rust, Director Virtual School of Molecular Sciences, domestic
net connection
VSMS http://www.nottingham.ac.uk/vsms, Virtual Hyperglossary
http://www.venus.co.uk/vhg

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