OASIS Mailing List ArchivesView the OASIS mailing list archive below
or browse/search using MarkMail.


Help: OASIS Mailing Lists Help | MarkMail Help

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index]
Re: [xml-dev] What is declarative XML? (And what's not)

Costello, Roger L. wrote:
> Do you agree that this stylesheet document is not a declarative XML document?
I don't think the opposite of "declarative" is really "procedural".  The 
opposite of "procedural" is "functional".  XSLT considered functional, 
not procedural, because functions do not have side effects (variables' 
values cannot be updated.)

The opposite of "declarative" is "algorithmic": declarative says what 
you want, algorithmic says how you do it.

So I think XSLT is declarative when using the template and XPaths, but 
algorithmic when using recursion. You can see that the use of  
<xsl:when> rather than <xsl:if> betrays the concern to try to be as 
declarative as possible.

There are implementation distinctions. The more declarative some program 
is, the more that it can be parallelized and optimized and have 
evaluation re-ordered. This is the same benefit that pure "functional" 
languages have, but "declarative" is not the same as "functional" and 
"algorithmic" is not the same as "procedural".

In your example, I think it is declarative, because there is just an 
identity established, and there is nothing given about how it should be 
implemented. The following two are algorithmic however:
   (map 'sum xpath(  "/purchases/merchandise/cost" ))
   int cost[] = get-xpath( current-doc, "/purchases/merchandise/cost" );
   int value = 0;
   for-each (cost) {
         value += cost;

In XSLT you cannot tell how a built-in function is implemented: just 
invoking a function is declarative IMHO.
Rick Jelliffe

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index]

News | XML in Industry | Calendar | XML Registry
Marketplace | Resources | MyXML.org | Sponsors | Privacy Statement

Copyright 1993-2007 XML.org. This site is hosted by OASIS