RE: SAX2: Another thought on subtyping, modification, etc.
David Megginson wrote, > I was thinking about this problem last night, and it > occurred to me that the ability to query and set > features and properties might be useful not only for > parsers but also for handlers, and perhaps for > specialised data structures of some sort. If that's > the case, then a separate interface makes a lot of > sense <snip/> That'd be quite a nice why of making what would've been a wart into a feature. Unfortunately I'm not sure that there really is anything that can be usefully done with the Configurable interface on anything other than Parser. Who would use it? Not a Parser surely: a general purpose parser can't be expected to do anything very much with any special features of the innumerable client-side handlers that might be plugged into it. The client itself? Well, if the client needs to support extended functionality on its handlers it should just define a clean, strongly- typed extended interface and use that directly. To do otherwise would be poor software design practise. In part the reason for this contrast (between Parser and the other interfaces) is that parsers represent a relatively tightly constrained domain: that means there's a reasonable prospect of providing access to their functionality via a reasonably simple, well defined interface, and being able to reuse them via that interface. SAX1 has done that up to now, but it's become clear over time both that some extensions are necessary for some applications, and that those are not necessarily desirable in all parsers. That, to my mind, is enough to motivate David's extensibility mechanism for SAX2. Handlers, on the other hand, don't represent anything like so tightly constrained a domain: they represent what an application _wants_to_do_with_ a parser, and there's no way we can set bounds on that. This being so, we shouldn't expect handlers to be particularly reusable, and so the pressure to find an extensiblity mechanism for them is considerably less than it is for parsers. Cheers, Miles -- Miles Sabin Cromwell Media Internet Systems Architect 5/6 Glenthorne Mews +44 (0)181 410 2230 London, W6 0LJ msabin@c... England xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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