xsl-list
[Top] [All Lists]

RE: [xsl] Replace content of element, then transform it...

2012-08-30 11:16:43
Wendell,

Thanks for a very informative answer. 
Yes, the XML I am receiving is poor by design, but has been chosen because the 
input system opens for non-valid XHMLT/XML. 
As I am trying to manipulate those who have taken this decision I sort of have 
option 0.

Found a bugreport on Firefox not supporting d-o-e where they have a 
doe.xsl-file, so I am following that route at the moment. Looks sort of OK, but 
since I am currently playing with controlled test-data and not real life 
examples, who knows when this will break...

I will look at the saxon::parse() function that you are referring to... And 
yes, if the XML/Source is valid or not...


Thanks
Trond Husø



Trond,

Indeed, your case illustrates exactly why disable-output-escaping is a trap.

One might think that if you have

<e>&lt;f>g&lt;/f></e>

and then

<xsl:template match="e">
   <xsl:copy>
     <xsl:value-of select="." disable-output-escaping="yes"/>
   </xsl:copy>
</xsl:template>

you then get <e><f>g</f></e>.

And this might even be true, in some cases -- but not in all. The reason? 
"<e><f>g</f></e>" is a sequence of characters, and XSLT does not generate 
sequences of characters, but nodes arranged in trees. You get a sequence of 
characters only when some subsequent process creates one from a tree generated 
by the transformation.

In this case, the tree would be shaped like this:

- element 'e'
   - text '<f>g</f>'

The process that turns this into an XML representation (tags and text: 
"<e><f>g</f></e>") is called "serialization".

In your case, however, having generated such a tree, your XSLT submits it to be 
processed with a set of templates. No markup is created at all until the 
*final* result of your processing pipeline is written in the form of characters.

There is no 'f' element to be matched and processed in this second step.

Among other consequences of working with trees (by and large beneficial ones), 
this means that the design pattern of "hiding" markup inside XML by escaping it 
is a poor one, which is bound to create problems. At best it works only if it 
is carefully managed.

How to manage it (assuming you can't change your input data)? You have two 
choices:

1. Serialize your intermediate results before processing it again. 
(Split your stylesheet into two, and run the second on the serialized output of 
the first.) This can work, but it doesn't scale well, as it requires both 
serializing and then parsing again in the middle of every transformation. Even 
with solid-state storage devices, this tends to be
time- and resource-intensive. And it locks you down to certain kinds of 
transformation architecture (namely on a file system).

2. Find another way of parsing the pseudo-markup hidden in your data. 
For example, use an extension such as saxon:parse(), which will turn a string 
into a tree of nodes (assuming it's well-formed XML).

Cheers,
Wendell

On 8/30/2012 9:01 AM, trond(_dot_)huso(_at_)ntb(_dot_)no wrote:
Right. I take that note.

I am also noticing that disable-output-escaping is deprecated in XSLT2.0, so 
I guess I shall try and figure out another way of doing this...

Trond


-----Original Message-----
From: Michael Kay [mailto:mike(_at_)saxonica(_dot_)com]
Sent: 30. august 2012 14:37
To: xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com
Subject: Re: [xsl] Replace content of element, then transform it...

One of the main reasons that we've been telling people for 12 years not to 
use disable-output-escaping is that it couples the transformation too closely 
to the serialization, meaning it's difficult and inefficient to reuse your 
code as part of a pipeline. A lot depends on what this d-o-e stuff is really 
doing. Having said that, from the information supplied I don't know why you 
are getting the error you are.

Michael Kay
Saxonica


On 30/08/2012 12:08, trond(_dot_)huso(_at_)ntb(_dot_)no wrote:
Hi,

I have the following XSLT.
<xsl:template match="body">
          <body>
              <xsl:value-of select="." disable-output-escaping="yes"/>
          </body>
      </xsl:template>

      <xsl:template match="leadtext">
          <leadtext>
              <xsl:value-of select="." disable-output-escaping="yes"/>
          </leadtext>
      </xsl:template>


      <xsl:template match="node()|@*">
          <xsl:copy>
              <xsl:apply-templates select="node()|@*"/>
          </xsl:copy>
      </xsl:template>

Which does what is intended. Just that I want to not output it, but start w= 
orking on it in a phase-two process.
So I tried this

<xsl:template match="body">
          <body>
              <xsl:value-of select="." disable-output-escaping="yes"/>
          </body>
      </xsl:template>

      <xsl:template match="leadtext">
          <leadtext>
              <xsl:value-of select="." disable-output-escaping="yes"/>
          </leadtext>
      </xsl:template>


      <xsl:template match="node()|@*">
          <xsl:variable name="foo">
          <xsl:copy>
              <xsl:apply-templates select="node()|@*"/>
          </xsl:copy>
          </xsl:variable>
          <xsl:apply-templates select="$foo" mode="phase2" />
      </xsl:template>
<!-- Error message:
Description: Cannot create an attribute node (id) whose parent is a 
documen= t node
-->

After reading about how this works, I now understand why I am getting the e= 
rror. Is there another alternative to make this possible in one document, o= 
r do I have to send the output to a new document?

Best regards,

Trond Husø
System Developer
Mobile : +47 450 35 715
E-mail : trond(_dot_)huso(_at_)ntb(_dot_)no
www.ntb.no

--
======================================================================
Wendell Piez                            
mailto:wapiez(_at_)mulberrytech(_dot_)com
Mulberry Technologies, Inc.                http://www.mulberrytech.com
17 West Jefferson Street                    Direct Phone: 301/315-9635
Suite 207                                          Phone: 301/315-9631
Rockville, MD  20850                                 Fax: 301/315-8285
----------------------------------------------------------------------
   Mulberry Technologies: A Consultancy Specializing in SGML and XML 
======================================================================

--~------------------------------------------------------------------
XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list
To unsubscribe, go to: http://lists.mulberrytech.com/xsl-list/
or e-mail: <mailto:xsl-list-unsubscribe(_at_)lists(_dot_)mulberrytech(_dot_)com>
--~--


--~------------------------------------------------------------------
XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list
To unsubscribe, go to: http://lists.mulberrytech.com/xsl-list/
or e-mail: <mailto:xsl-list-unsubscribe(_at_)lists(_dot_)mulberrytech(_dot_)com>
--~--