Hi Sedna Team and Sedna Users,
I don't know what plans there are, if any, for Sedna to change the
current update language based on XQuery update proposal by Patrick Lehti
(with Sedna improvements) to support the up-coming W3C XQuery Update
Facility (XQUF). (See latest W3C Candidate Recommendation is at this link:
http://www.w3.org/TR/xquery-update-10/ ).
At the moment, the current Sedna update language works quite well and
supports all of the use cases that I've come across for updating XML
documents. Perhaps one could say "If it isn't broke, don't fix it."
But just in case the team is thinking about supporting XQUF, I would
like to point out that the current Sedna update language supports more
XML update use cases than the new W3C proposal. These are as follows:
UPDATE delete_undeep. There does not seem to be a direct translation of
this construct in XQUF although it appears that it can be achieved using
an XQUF transform expression together with a replace updating
expression. May I ask for comments on this please. (Perhaps I've missed
something in the XQUF spec).
UPDATE replace. With this statement, Sedna currently allows changing an
element into an attribute. In my opinion this is good because it is
quite comment to write some XML using and element to hold simple data
and then change your mind and decide to replace it with an attribute
(and vica versa). For example you might start with this:
<invoice>
<amount>1000000.00</amount>
<description>A very large order</description>
</invoice>
and then change your schema to this instead:
<invoice amount="1000000.00">
<description>A very large order</description>
</invoice>
The Sedna statement to perform this update is:
UPDATE replace $a in (path-to-invoice element)/amount with attribute
amount {"1000000.00"}
With the new XQUF you cannot do this (an element cannot be replace with
an attribute) and instead you have to write this with two expressions:
one update expression to delete the amount element and one update insert
expression to insert a new amount attribute.
See section 2.4.3.1 Replacing a Node in the XQUF spec.
http://www.w3.org/TR/xquery-update-10/#id-replacing-node
For my taste the XQUF spec is broken in this respect and I would feel
inconvenienced to lose the functionality that the current Sedna update
language offers.
I think the above are important issues for Sedna users so what do others
think?
Cheers
Justin Johansson
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