W3C home > Mailing lists > Public > public-qt-comments@w3.org > July 2005

integrating assign in the standard

From: Andre Cusson <ac@hyperbase.com>
Date: Sun, 03 Jul 2005 19:33:03 -0400
To: public-qt-comments@w3.org
Message-id: <6.2.1.2.0.20050703164703.01e91898@pop.hyperbase.com>
Hi,

There has been recent issues and discussions about the support of "assign" 
and associated functionality, ex:
- the "Template recursion, StackOverflowError, saxon:while and variable 
assignability" message track on saxon-help@lists.sourceforge.net, continued on
- the 
"<https://sourceforge.net/forum/message.php?msg_id=3212142>Eliminating 
saxon:assign" message track of the source-forge Saxon OpenDiscussion forum 
at https://sourceforge.net/forum/forum.php?thread_id=1305798&forum_id=94026).

Assign is currently an extension supported by some implementations (ex: 
Saxon).

Recently some have been proposing to drop assign from XSLT as there should 
be other (more standard) ways to achieve equivalent results.

We have been looking at this for little while and would like to propose not 
only that assign could be supported as an extension but that assign should 
be an integral part of the XSLT standard for the simple reason that 
important and fundamental processing patterns can not be efficiently 
expressed in XSLT, without assign.  These assign dependent processing 
patterns map-out to many essential and often non-trivial use-cases, and 
include:

- support of (user) global variables in scripting languages written in XSLT 
(like the XML-based layout scripting language of our publishing engine)

- efficient run-time traversal and processing of large networks while 
avoiding loops (like traveling salesman trying to mark paths that he has 
already visited, as he traverses the graph)

- efficiently record and monitor global processes (like avoiding the 
XSLT2.0 "Cannot write more than one result document to the same URI" error 
(and avoiding duplicates/overwrites) when re-generating (ie. updating), 
from its XML sources, a web site, whose pages are already referred to by 
other sites and bookmarks, and where, while traversing the tree of source 
XML documents, at every page node, before generating the page, the 
transform needs to check if that URL has already been used, add it to the 
list of done pages if it has not or report (ex: trace) the duplication.


For real-world examples, we have an XSLT application currently on-line, 
with about 25K lines of XSLT 2.0 and about 400 global variables of which 17 
are assignable variables that specifically fit patterns for which no other 
equivalent algorithm could be found to replace the ones using assign, 
confirming (still, so far), the requirements for Assign.

In fact, assign is so important, that it has to be part of the standard 
(like regex, number formatting, escaping, html serialization, keys, etc.) 
to allow non-trivial applications to be conformant and portable.

In no way are we advocating that assign should be used in cases other than 
those for which there is no reasonable alternative.

Of course, the name "assign" is not really important, but it is the 
occasional mutability offered by the associated functionality that is key 
and unique.

Do not hesitate to contact us for more information.

Thank you for your consideration.

Andre Cusson
T: (1) 514 583 0601
01 COMMUNICATIONS
Received on Sunday, 3 July 2005 23:31:10 UTC

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