[XSL-LIST Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message]

Re: Re: An issue with XPath 2.0 sequences (Was Re: RE:

Subject: Re: Re: An issue with XPath 2.0 sequences (Was Re: RE: Muenchian method, and keys 'n stuff)
From: Dimitre Novatchev <dnovatchev@xxxxxxxxx>
Date: Thu, 31 Jan 2002 02:49:49 -0800 (PST)
xml empty element
Joerg Pietschmann <joerg dot pietschmann at zkb dot ch> wrote:

> Dimitre Novatchev <dnovatchev@xxxxxxxxx> wrote:
> > Several people already expressed their curiosity about what was the
> > reason to forbid a sequence to have an element-sequence.
> Well, i can see people getting uneasy about sequences containing
> empty sequences. In particular there may be conflicting expectations
> how to interpret a sequence containing an empty sequence in various 
> boolean contexts. In my LISP days i've seen quite a few people
> hunting bugs ultimately caused by the difference between NIL
> and '(NIL). There may be also problems in how to handle empty
> sequences in unions and other functionality: should the result
> of (())|(()) be (()) or (()()) or even ()? 
This shouldn't be a problem. However, it will be more correct to speak
about concatenation of sequences, not union, because sequences are not
sets, sequences are ordered and sequences can haverepeating identical
elements. Sequences, whose elements may be sequences are
straightforward to model with node-sets (trees):


is the same as 

$S1 | $S2,

where $S1 and $S2 each contain:


The result of their concatenation (not union!) will be:


> Should sum((1 () 2))
> result in 3 or NaN?

In a strongly typed system this results in error, because the sum()
function is defined over sequences of numbers, and the second element
of(1 () 2) is not a number. 

> Having said that, i still think it would be much cleaner to
> allow sequences containing sequences, even if it breaks some
> existing style sheets.

As Mike pointed out, the decision to have sequences only of
simple-valued elements closely reflected the XML-Schema datatypes.

It must be noted, that sequences without such restriction cover
completely the XML-Schema-type sequences, so their use in XPath will
not lead to any contradiction with XML-Schema.

Dimitre Novatchev.

Do You Yahoo!?
Great stuff seeking new owners in Yahoo! Auctions! 

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list

Current Thread


Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced!

Buy Stylus Studio Now

Download The World's Best XML IDE!

Accelerate XML development with our award-winning XML IDE - Download a free trial today!

Don't miss another message! Subscribe to this list today.
First Name
Last Name
Subscribe in XML format
RSS 2.0
Atom 0.3
Site Map | Privacy Policy | Terms of Use | Trademarks
Free Stylus Studio XML Training:
W3C Member
Stylus Studio® and DataDirect XQuery ™are products from DataDirect Technologies, is a registered trademark of Progress Software Corporation, in the U.S. and other countries. © 2004-2013 All Rights Reserved.