Re: [xml-dev] What is declarative XML? (And what's not)

[Nicholas Sushkin <nsushkin@openfinance.com>]

On Wednesday 03 June 2009 19:31, Costello, Roger L. wrote:

> I'd like for us to nail down exactly what we mean by "descriptive markup"
> and "algorithmic markup."

On Thursday 04 June 2009 03:06, Michael Kay wrote:

> Why, what do you hope to achieve?


I thought the whole point of trying to separate the two types of markup was 
to figure out which kind of markup allows limited computing power necessary 
to deduce its meaning. 

To make a decision based on a descriptive markup, you don't need to 
implement a Turing machine who noone knows when it will stop. So, 
descriptive markup is the markup whose meaning can be deduced in a bound 
finite time. To make a decision based on algorithmic markup, you would have 
to execute the algorithm. 

The same markup can be descriptive or algorithmic based on what decision 
you're trying to make. Imagine an XSLT stylesheet. If you want to figure 
out whether the stylesheet takes a parameter named "starting_date", the 
markup is descriptive because you can figure out the answer with a simple 
XPath expression you know is bound to produce the answer in a finite time. 
If you want to figure out the result the stylesheet, the XSLT markup is 
algorithmic. You'd have to build and run the actual XSLT processor to 
figure it out. 

http://en.wikipedia.org/wiki/Undecidable_problem

ps. Just my take on the discussion
-- 
Nicholas Sushkin, Senior Software Engineer
http://www.openfinance.com http://www.wealthinformationexchange.com

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