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Re: Penance for misspent attributes

• To: Bill de hÓra <dehora@e...>
• Subject: Re: Penance for misspent attributes
• From: Dennis Sosnoski <dms@s...>
• Date: Sun, 19 May 2002 18:45:29 -0700
• Cc: xml-dev@l...
• References: <000801c1fd9d$8778fab0$887ba8c0@mitchum>
• User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:0.9.8) Gecko/20020205

SAX is great for generic XML handling - it's easy to hook up a handler 
for building a document representation using DOM or some other model, 
for instance. It's very awkward for direct processing by an application, 
though, and I think autogenerating state machines just add another layer 
of complexity.

Pull parsers seem a better approach for this type of application. Using 
a pull parser gets you away from all the problems of event-driven state 
machine programming and lets you process the document structure 
directly. You can see my JavaWorld comparison at 
http://www.javaworld.com/javaworld/jw-03-2002/jw-0329-xmljava2.html for 
some discussion and code examples on this topic.

The only real problem with using pull parsers right now is limited 
availability. The XMLPull site at http://www.xmlpull.org has details of 
the common interface implemented by two pull parsers currently (with 
hopefully more to come), so it's a big step in the right direction. 
There's also a JSR in progress (JSR-173) to develop a Java standard API 
for pull parsers.

  - Dennis

Bill de hÓra wrote:

> 
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>Hash: SHA1
>
>
>>-----Original Message-----
>>From: Sean McGrath [mailto:sean.mcgrath@p...] 
>>
>>There is more to it than a buffer. Parsers can and do emit 
>>chunks of content at boundaries that suit themselves. So
>>
>><foo>
>>Hello world
>></foo>
>>
>>is not guaranteed to produce 1 data event that can be slurped 
>>into a buffer in one go. More generally, in the presence of 
>>mixed content there will definitely be multiple chunks. So 
>>you end up with this pattern:
>>
>>start_foo:
>>	buffer = ""
>>	inFoo = 1
>>
>>end_foo:
>>	print buffer
>>
>>characters (chunk):
>>	if inFoo:
>>		buffer.append (chunk)
>>
>>This rapidly gets out of hand.
>>
>
>Yes it does. However we can start to accept we're hacking a state
>machine and encapsulate the conditional reasoning:
>
>start_foo:
>	enterState(start_foo)
>
>end_foo:
>       getHandler().execute()
>       leaveState(start_foo)
>
>characters (chunk):
>	getHandler().accept(chunk)
>
>this can be data driven and very fast; it works much like a simple
>dispatching server or the lookup tables common enough in game
>programming. Granted we've been here before about how developers
>find state machines awkward but it does leave open the possibility
>of being declared and then autogeneratated. Was this approach never
>taken with SGML? There doesn't seem to be a lot work being done in
>the public domain to codegen saxhandlers (maybe I'm looking in the
>wrong places), but I expect it will become common enough. I'm
>pretty sure people are using Maps and the like to key event
>handlers, but I haven't seen it in the wild. 
>
>Bill de hÓra
>
>
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>
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    • From: Bill de hÓra <dehora@e...>

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