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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Feasibility of "do all application coding in the XML langu
 Hi, I am curious how you would contrast this to using the doc function and a custom URIResolver (in java, which is what I tend to do). For instance, doc(check-to-see-what-i-might-need)/* then loop through those things doc(some-thing)/* the URIResolver returns the thing you need without the XSL/XQuery knowing anything about what went on to make it happen. -Rob On Dec 3, 2008, at 2:33 PM, Thomas Lord wrote: > Kurt, > > In my Flower project (temporarily off-line but it'll be back) > I explored a "third way" relative to what you are talking > about. > > > XQuery and XSLT should remain purely functional (aka > declarative). > > Non-standard "extension functions" should be avoided > almost always, for at the very least the break portability. > Commonly, extension functions are poorly designed in that > they sneak in non-declarative, sequencing semantics. > > Pipelines (e.g. XProc) aren't flexible enough regarding > side effects and flow of control. For example, > in most pipeline systems, you can't do recursion. > > Instead, I invented a kind of "I/O monad" for running > XQuery and XSLT scripts in a kind of continuation passing > style. A computation (say, in XQuery) returns a > list of side-effecting operations to perform plus a > continuation. The continuation is itself a second > XQuery script. The monad performs the side-effecting > operations, packages up the results as XML Datums, > and invokes the continuation. Repeat in a loop > until eventually a "null" continuation is returned. > > If you want to add, say, an FFT function -- don't > bind it into XQuery as an extension function (thereby > dragging in hundreds of thousands of lines of code > including a complete graph-tracing GC where less than > 10K lines of code are needed). Rather, package the > FFT in a web service API: the I/O Monad calls out to > it and then resumes XQuerying. The FFT engine > can be same-process or could be remote -- only performance > will differ. > > It's then desirable to create syntactic abstraction > mechanisms over XQuery.... > > -t > > > > On Wed, 2008-12-03 at 11:08 -0800, Kurt Cagle wrote: >> >>> yea, but a lot of people are using it like PHP rather than a >> replacement for >>> SQL on XML. It is the way XML DB vendors recommend you make >> webapps. >>> Writers/editors (at least the ones I have been reading) seem >> to think this >>> is the way to go. It seems like a step backwards. >> >> >> Not sure I'd completely agree with that (of course I'm one of the >> writer/editors that's been advocating this approach). If XQuery >> +extensions was purely declarative, then the filter approach works >> fine, but in point of fact one of the most significant changes taking >> place in the XQuery space is the introduction of database modifying >> code. Once that happens, then realistically you do have to think >> about >> XQuery as being at a minimum part of a processing pipeline and quite >> possibly the only part of that pipeline This changes the dynamic for >> XQuery pretty dramatically, and moreover it does so by reducing the >> processing of a servlet into a complete XML environment. >> >> However, the key here is again to keep the XQuery as simple (and >> standardized) as possible - There's an interesting recurrent Filter >> -> >> Sort -> Partition (Page) -> Style pattern that seems to show up over >> and over again in the XQuery I work with, for instance, and XQuery >> works remarkably well when you deliberately keep your systems as >> RESTful as possible. >> >> Is that the only use for XQuery? No, of course not, but from a web >> development standpoint it is a primary pattern. Like everything else, >> it works best when you avoid inlining XQuery and XML markup (one >> reason that PHP, or most server-side code constructs, can be such a >> pain), but that's a lesson that only seems learned by experience. >> >> >> > 
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