[Monetdb-developers] New vs. Existing Update Syntax

Jens Teubner jens.teubner at in.tum.de
Thu May 18 13:10:19 CEST 2006


On Thu, May 18, 2006 at 12:29:30PM +0200, Sjoerd Mullender wrote:

> >  -- It is not clear to me how our current insert-...() functions
> >     handle attributes in the new node list.
> 
> The new nodes may contain attributes.  They are inserted with the new
> nodes.

Just to be sure we don't misunderstand each others: I was talking about
attribute nodes in the argument to the insert-...() functions, _not_
about attributes that belong to some element in the function argument.
I.e., given the document foo.xml:

  <?xml version='1.0'?>

  <x>
    <y/>
  </x> ,

will the statement

  insert-first (doc("foo.xml")/x, attribute foo { 42 })

enrich the root node of the document with a new attribute, resulting in

  <?xml version='1.0'?>

  <x foo="42">
    <y/>
  </x> ,

On the system I tested this situation led to weird MIL errors only.

(Note that the insert function are declared as
`fn:insert-first (node, node)', etc.  So they should accept all node
kinds in both arguments.)

> >     The W3C draft provides separate upd:insertAttributes ($element,
> >     $attlist) and upd:insertBefore ($element, $nodelist) functions
> >     (and similar).  The translation from the surface syntax to the
> >     update operations then takes care of invoking the right
> >     functions.
> 
> Is upd:insertAttributes similar to our set-attribute function (except
> that set-attribute works on a single attribute)?

Yes, I think so.

But this is not actually the problem we have.  I will try to illustrate
the problem.  The query

  do insert (attribute foo { 42 }, element bar { 17 })
    as first into fn:doc ("foo.xml")/x

should modify the above mentioned XML document to

  <?xml version='1.0'?>

  <x foo="42">
    <bar>42</bar>
    <y/>
  </x> .

So the "SourceExpr" for the `do insert' statement is allowed to contain
attributes as well as other node kinds.  The specs then say that we have
to add the attributes using upd:insertAttributes(), the rest via
upd:insertBefore().  We do have both update functions.  What do _not_
have is a means to _separate_ the attributes from the remaining node
kinds in XQuery Core.  This is why I was asking if our implementation of
the insert-...() function can cope with attributes.  If that was the
case, we would not need upd:insertAttributes() at all for this situation
and handle everything in upd:insertBefore()/fn:insert-before().
    
Regards,

Jens

-- 
Jens Teubner
Technische Universitaet Muenchen, Department of Informatics
D-85748 Garching, Germany
Tel: +49 89 289-17259     Fax: +49 89 289-17263

Real programmers don't comment their code.
If it was hard to write, why should it be easy to read?




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