SAX: Next Round

david at david at
Thu Jan 21 02:57:31 GMT 1999

John Cowan writes:

 > David Megginson scripsit:
 > > I'd like to lose EntityResolver and DTDHandler (who uses them?),
 > > but I don't know if we can.
 > Nope, nope, nope.  In particular, I still have a project to finish
 > a standard EntityResolver that understands Socats.  By having such
 > a thing, you can fit Socat support into arbitrary applications
 > using arbitrary SAX parsers.  Keep it.  As for DTDHandler, it
 > exposes stuff that XML 1.0 requires a parser to expose.

Yes, yes, yes, I know -- I've made the same argument before in many

In retrospect, I think that unparsed entities and notations were a
mistake for XML (there are less opaque and more web-friendly ways to
accomplish the same thing), but they're there in the REC and, as you
say, the spec is quite explicit about reporting requirements.  I was
just fantasising out loud...

 > > 1. Filter Interface
 > I propose a fourth alternative: provide ParserFilter as a helper
 > class, and don't have a separate interface.  Parser filters are
 > just parsers that have a "parser(Parser)" constructor.

Yes, but what interface should the helper class implement?  Will have
have a hard-coded level-two parser interface that knows about
namespace and lexical handlers?  What if we add another standard
capability in the future?

The advantage of a separate interface is that it's easy to mix and
match; the disadvantage of a separate interface is also that it's easy 
to mix and match.

 > One particularly nice feature of this is that it is the pattern
 > used by Java {Input,Output}Streams and Readers/Writers: Chain of
 > Responsibility.

I agree -- chain of responsibility is a great benefit of the filter
approach, however we manage it.

All the best,


David Megginson                 david at

xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev at
Archived as:
To (un)subscribe, mailto:majordomo at the following message;
(un)subscribe xml-dev
To subscribe to the digests, mailto:majordomo at the following message;
subscribe xml-dev-digest
List coordinator, Henry Rzepa (mailto:rzepa at

More information about the Xml-dev mailing list