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XML Co-Creator says XML Is Too Hard For Programmers
orangerobot writes "Tim Bray, one of the co-authors of the original XML 1.0 specification has a new entry on his website explaining why he's been feeling unsatisified lately with XML and says his last experience writing code for handling XML was 'irritating, time-consuming, and error-prone.' XML has always a divided response among the technical community. The anti-XML community has several sites stating their positions."
Tim Bray thinks that callback based XML apis are a bit awkward to use. He would prefer to use something like a pull parser (see for example http://www.xmlpull.org for examples in java) to the current perl xml apis.
And he would probably want to be able to parse parts of documents ("XML Fragments"), rather than whole documents.
I agree with his views (not using perl too much, though). But this is *not* the end of XML or anything. Tim just has some thoughts about how the xml api could be better in perl. Not very exciting, perhaps...
WTF? Perhaps you could explain more about these two cases. As far as I know, general XML parsers such as Expat do not require unlimited memory to parse any finite input document, nor do they require infinite time.
The Document Type Description (DTD) system is equivalent to a BNF grammar for XML documents. It's not quite as flexible as a full BNF because it enforces that elements are correctly nested, but I don't see this as a bad thing.
And yes, DTDs are machine readable. Other grammars for XML documents such as DSD, XML Schema or Relax-NG are also machine readable.
Just as with BNF grammars and flex(1), you can take a DTD and generate an efficient parser from it using FleXML.
Comparisons with TeX aren't really appropriate because TeX is a Turing-complete language, and so impossible to parse automatically in 100% of cases (unless you want to allow that your program will sometimes fail to terminate, ie hang, on particular input files). I don't know what you mean by your subject line 'Maybe he should have read Knuth'...
-- Ed Avis ed@membled.com
Well, I've written my own XML parser, as well as a compiler for a simplified version of C, so I think I'm somewhat qualified to talk on this. A generalized XML parser is not memory intensive, unless you are a very bad programmer. All you need is a depth-first stack, which will be as high as your XML tree is deep. And given that, a stack of size N is capable of handling a tree of size X^N, you are definitely going to run out of disk space before you run out of RAM. In other words, the memory required for parsing an XML tree is trivial.
An XML parser is one of the simplest parsers imaginable. It's a sophmore task to create a state machine to process the generic L(1) (or is it L(0)?) XML grammar. And as you should know, a state machine for an L(1) grammar is as fast as you can get.
Anything you do with regular expressions will be much more complicated. As I'm sure you know, regular expressions are turned into state machines before being used to process the input. And almost all regular expression state machines are much more complicated than the state machine you need for an XML parser. In an XML parser, definite boundaries exist on elements such as:
Regular expressions are not this smart. For example, looking for the substring "abc" in the longer string "abababaaabbbabcabababac" is already generating a statemachine that is more complicated than that needed for XML parsers.
Back to the "memory" intensive nature of XML parsers. If you parse your XML tree into a nested hashmap structure, then the memory needed will be proportional to the number of nodes in the XML tree. Maybe this is what you meant by "memory intensive". However, this is totally unnecessary. You can easily construct an XML parser to look for the specific elements you care about. Then you only get those elements, and you only need to allocate the memory for the elements required.