Re: [Xmldb-org-xupdate] Poorly defined update instruction

[John L. C. <jl...@po...>]

On Wed, May 11, 2005 at 04:42:43PM -0700, Ronald Bourret wrote:
> John L. Clark wrote:
> >I would prefer that the latter be made normative (that is, that
> >update be treated precisely as node replacement, hence my original
> >argument about the assignment operator semantics).
>=20
> I prefer content replacement to node replacement. Node replacement would=
=20
> mean that if I selected the node <date>10/11/12</date>, I would have to=
=20
> include the <date> markup in my update instruction, which feels=20
> unnatural when all I want to do is change the date.

The content of an element is a node[0].

If all you want to do is change the date, then you want to change the
date element's content node, not the date node itself.  More precisely,
the node you want to change is represented by the XPath expression
/date/text(), which more precisely expresses the target of the
replacement (that is, the text, *not* the whole element).  I think this
is why it feels unnatural; if you want to change the whole element, then
you should both address that element precisely and include the new
element in the update content.  This example is akin to my modification
of the example from the specification:

---
<xupdate:update select=3D"/addresses/address[2]/town/text()[1]"
  xmlns:xupdate=3D"http://www.xmldb.org/xupdate">New York</xupdate:update>
---

Which selects the first text node within the town element and chooses to
update *that*.  In your example, you don't want to update the whole
element, just the text child of that element (informally, that element's
content), and so I think that you should be required to address the node
that you want to update precisely.

> This also shows why it would be useful to have an xupdate:replace=20
> element as Wolfgang suggests. This would allow me to replace the <date>=
=20
> element with <birthday>, for example. To my mind, this is very distinct=
=20
> from changing a value.

As detailed above, I disagree.  You can use the current xupdate:update
to satisfy both of these use cases with an appropriate XPath expression.

Take care,

    John L. Clark

[0] http://www.w3.org/TR/xpath.html#data-model