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   Re: [xml-dev] Are Updates really needed in XQuery?

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We have found many applications needing an update capability, but 
usually combined with the ability to find out if an update is needed, 
i.e. a comparison capability that is XML-aware. DeltaXML is based on 
this, i.e. finding changes to XML documents/data and representing 
these in XML.

XML is extensively used for data, and most data changes. So to be 
able to find the changes intelligently and provide an update 
representation in XML is useful. The way we represent such updates 
means that they can be processed as normal XML, so we do not use 
XPath (partly because DeltaXML pre-dates XPath, but also because for 
extensive changes/updates across a large XML file Xpath is not the 
best way to represent it).

XML file versioning is one application - the ability to store deltas 
to roll-forward or roll-back. If data sets are large, it makes no 
sense to store all the data each time. To be able to represent 
changes to XML data as XML opens up a whole set of new possibilities 
in XML applications, e.g. display/process changes to a data set.

You can see how this works on our web site (http://www.deltaxml.com), 
but we are certainly finding many applications that need to provide 
an update capability! This does not mean that it should be part of 
the XQuery language, of course.


At 5:56 am -0800 29/1/02, Brian Vickery wrote:
>I have a simple question, "Why do we need updates as part of the XQuery
>language at all?"
>I have read the latest XQuery Update proposal (from the "XQuery Update
>Proposal" by Patrick Lehti) and the older XUpdate WD.  I come from a
>database background and view updates as imperative to the XQuery/XPath
>language, but can't state "why".  I'm getting a lot of grief regarding
>having Updates at all.  The types of "inserts" and "deletes" typically shown
>are just adding/deleting a document from a "collection" (if collections
>existed and they should IMHO).
>Some examples are:
>1.  If I have a collection of XML invoices why would I ever want to update
>these?  An invoice is written once and never changed!
>2.  If I have a document centric collection of XML document I would most
>likely version each document, thus why do we need updates?
>3.  If I have all my business contacts (companies I do business with) stored
>in an XML collection, why wouldn't I just do a complete replace if I wanted
>to change a companies name or address?
>Does anyone have any real life scenarios/business cases that "MUST" have
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-- -----------------------------------------------------------------
Robin La Fontaine, Director, Monsell EDM Ltd
DeltaXML: "Change control for XML in XML"
Tel: +44 1684 592 144 Fax: +44 1684 594 504
Email: robin.lafontaine@deltaxml.com      http://www.deltaxml.com


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