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--- Patrick Lehti <Patrick.Lehti@ipsi.fhg.de> wrote:
> IMHO, typing of updates does matter. It is even more
> important, than
> typing of queries itself, because
> you are changing the state of your database!
> Just think of an XML document of some GBs of size
> and you want to change
> a greater amount of nodes in that document with your
> update query. Do
> you really prefer a post-update validation of the
> complete document
> against a static type check of the update query?
> Don't forget: if the
> validation fails, you have to do a very expensive
> rollback on your
> database! And what about developing the update
> query, do you want to do
> these post-update validation and rollback steps
> until you completely
> debugged the query and it is working as you
> expected?
>
Actually, I don't expect something that expensive.
What I would like is for post-update validation to be
the the most that is required by a DML specification
giving implementations leeway to do more aggresive
validation if they can which I am sure many will (in a
way that would probably mimic much of the XQuery type
system without some of the more onerous obligations).
A post-update validation would be the minimum
requirements as opposed to the XQuery expensive static
& dynamic type checking as the minimal requirements
approach.
Secondly, XQuery doesn't really have a type system
because it uses W3C XML Schema which is a validation
system. Thus many of the things the XQuery type system
is supposed to catch can also be caught by an
aggressive validator. Even then many W3C XML Schema
issues still need to be handled by post-update
validation since XQuery punts on them (e.g. identity
constraints, user defined type hierarchies by
restriction or extension, etc). So a W3C XML Schema
aware DB that uses XQuery still needs to support
post-update validation to be fully compliant.
PS: Weird, I didnt get this email at my work address
even though it went out to XML-DEV.
DISCLAIMER: This is my personal opinion and does not
reflect the views, intentions, plans, or strategies of
my employer.
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