[xquery-talk] RE: Future of XQuery and XQuery Update Faclilty

Jonathan Robie jonathan.robie at redhat.com
Mon Oct 22 16:44:11 PDT 2007

Michael Kay wrote:
>> I don't follow you.   I don't see that at all.
> Well, the language semantics are expressed in terms of pending update lists,
> and you want to expose those pending update lists to the user. But an
> implementation only has to behave "as if" there were a pending update list.
> Internally, it might do the update immediately, detect conflicts as they
> arise, and roll back to the original state if there is a failure. You're
> making it quite difficult to implement it that way if the PUL is visible to
> user applications.
> In the case of XQuery implementations built on top of an RDBMS, I would
> think they are likely to use the transaction manager of the database
> service.

Perhaps another way of putting it: what is central here is the updates 
that are to be done. To specify the updates to be done, an application 
would write queries that contain updates, it would not generate a 
pending update list in XML so that a different application can do the 
updates. Distributing a single update among multiple applications is not 
a simplification.

The pending update list is a way of defining the semantics of the 
language. We don't expose the formal semantics as XML either, nor the 
import mechanism, nor many other aspects of our semantics. Most users 
will use one XQuery engine for a given update, and simply issue an 
update and observe the results.


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