Re: [basex-talk] BUG node comparison

[ydyxeb]

Thank you very much Christian! (my mistake for confusing equality and 
inequality in consideration of your previous response)
Kind regards
Jan

-Original Message-
From: Christian Grün  
Sent: Wednesday, May 26, 2021 13:28
To: ydy...@post.cz
Cc: BaseX 
Subject: Re: [basex-talk] BUG node comparison

Hi Jan,

> However, I still don't understand, why the -w parameter should do the trick. 
> I would expect the parsing is done once on the document load and $rootElement 
> variable is just holding a document's node. Then string value of either 
> $rootElement and parent::* should be identical for identical nodes. Do I miss 
> something?

Yes, the parsing is done only once, and $rootElement will contain the root 
element of this document. Let’s assume we have this input
document:


  

  


If -w is omitted, the whitespaces (4 text nodes, in the example) will be 
dropped, and we’ll be left with the plain element structure:



Let’s now assume we have this query:

//c[.. != /a]

The path returns the element named "c" if the string value of its parent 
differs from the string value of "a":
• If the whitespaces of the document are preserved, the comparison
will be successful, because "a" has the string value "\n  \n\n
\n", whereas "b" has the string value "\n\n  ".
• If whitespaces are dropped, the comparison will return false, because the 
string values of both elements will be the empty string.

Does this make sense to you?
Christian

Re: [basex-talk] BUG node comparison

[ydyxeb]

Hi Christian,

thank you for the deep explanation. I've just got to use XQuery recently; my 
knowledge is primarily based on XPath 1.0 acquired 15y ago. I understand the 
underlying string value comparison of nodes/node sets. Even though performance 
was not my goal, thank you for the suggestion of 'is operator'. 

However, I still don't understand, why the -w parameter should do the trick. I 
would expect the parsing is done once on the document load and $rootElement 
variable is just holding a document's node. Then string value of either 
$rootElement and parent::* should be identical for identical nodes. Do I miss 
something?

Thank you,
Jan

-Original Message-
From: Christian Grün  
Sent: Wednesday, May 26, 2021 11:41
To: ydy...@post.cz
Cc: BaseX 
Subject: Re: [basex-talk] BUG node comparison

Hi Jan,

Thanks for your feedback to the mailing list.

Your query will return the expected paths if you call BaseX as follows:

basex.bat -w -i datafile.xml queryfile.xq

A short explanation: By default, BaseX ignores whitespaces when parsing XML 
documents. By specifying -w, whitespace chopping can be suppresed [1,2]. If you 
want to permanently disable whitespace chopping, you can achieve that by adding 
"CHOP=false" option in your .basex configuration file [2]

A more comprehensive explanation (just ignore it if you are aware of all the 
details): In your query, you are checking if the string value of a parent 
element is identical to the string value of $rootElement.
The following comparison is equivalent to yours:

//Section[parent::*/data() != $rootElement/data()]

This is the reason why it matters if the whitespace-only nodes will be parsed 
or not. – If your actual objective is to compare the XML structure, you could 
the following:

//Section[not(deep-equal(parent::*, $rootElement))]

The following solution compares node identities:

//Section[not(parent::* is $rootElement)]

Hope this helps
Christian


[1] https://docs.basex.org/wiki/Command-Line_Options
[2] https://docs.basex.org/wiki/Configuration



> Using BaseX 9.5.1, cmd-line “basex.bat -i datafile.xml queryfile.xq” 
> leads to no result at all. I’m convinced there should be result 
> equivalent to the one of the online xquery tester 
> (https://www.videlibri.de/cgi-bin/xidelcgi)
>
> For a modified query using string comparison based on fn:path(), BaseX gives 
> the expected result.
>
>
>
> %%% query begin %%%
>
> let $rootElement := /child::*
>
> for $x in //Section[parent::* != $rootElement]
>
> return fn:path($x)
>
> %%% query end %%%
>
>
>
> %%% data begin %%%
>
> 
>
> 
>
> 
>
> 
>
> 
>
> 
>
> 
>
> 
>
> 
>
> 
>
> 
>
> 
>
> %%% data end %%%
>
>
>
> %%% modified query begin %%%
>
> let $rootElementPath := fn:path(/child::*)
>
> for $x in //Section[fn:path(parent::*) != $rootElementPath]
>
> return fn:path($x)
>
> %%% query end %%%
>
>
>
> Kind regards
>
> Jan Červák

[basex-talk] BUG node comparison

[ydyxeb]

Dear BaseX,

 

according to github instructions I’m sending a bug report via email:

 

Using BaseX 9.5.1, cmd-line “basex.bat -i datafile.xml queryfile.xq” leads to 
no result at all. I’m convinced there should be result equivalent to the one of 
the online xquery tester (https://www.videlibri.de/cgi-bin/xidelcgi)

For a modified query using string comparison based on fn:path(), BaseX gives 
the expected result.

 

%%% query begin %%%

let $rootElement := /child::*

for $x in //Section[parent::* != $rootElement]

return fn:path($x)

%%% query end %%%

 

%%% data begin %%%

























%%% data end %%%

 

%%% modified query begin %%%

let $rootElementPath := fn:path(/child::*)

for $x in //Section[fn:path(parent::*) != $rootElementPath]

return fn:path($x)

%%% query end %%%

 

Kind regards

Jan Červák