Re: Should data be changed according to defaults in Schema?

"Weber, Heiko" wrote:
> 
> When the values are changed as they are entered, the defaults will
> only be defaults that apply to inserting the data and not for
> reading the data.  But isn't this also the case for defaults that
> are specified for tables in SQL? 

Yes (at least for Sybase), but RDBMS do not have to behave after an
existing document model.

The "semantic" of XML Schema default values is relevant in the context
of XML documents and their behavior is to replace values that are not
specified in the instance documents, not to modify the documents.

The issue you are rising is probably wider than this and I wonder if
your question shouldn't be:

Should we store the "raw" infoset of the documents or their "PSVI" ?

> Maybe we should have an attribute
> for the Schema which specifies if the Schema should be applied for
> inserting or retrieving data or both?
> 
> If I change the default values in a Schema, the data that was entered
> at the time when the default was still another value, might have
> assumed that the default at that time be used, so if I change the
> default at later point in time, all the values would change, which
> might not be wanted.  Maybe only all the new data entered from that
> point in time is inteded to take the new default values.
> 
> Since the Schema-Information is most likely also used for creating
> indexes for the database there will only be one single Schema that
> describes a dataset, so the data will not be accessible via different
> Schemas at the same time.
> 
> It would be interesting to find out how current databases have solved
> this problem...

Do you know how does Tamino does behave ?

Eric
 
> thanks,
>    Heiko Weber
> 
> --- --- --- --- --- --- --- --- --- --- ---
> 
> Software AG Germany
> DBMS Open Systems Development (XML)
> Uhlandstrasse 12
> D-64297  Darmstadt
> Germany
> 
> Email:  mailto:Heiko.Weber@softwareag.com
> Web:     http://www.softwareag.com
> 
-- 
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Eric van der Vlist       Dyomedea                    http://dyomedea.com
http://xmlfr.org         http://4xt.org              http://ducotede.com
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Received on Friday, 2 February 2001 06:43:01 UTC