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   RE: 2 WAY - Programming "Glue Layer" between the database and XML and ba

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  • From: Ronald Bourret <rbourret@ito.tu-darmstadt.de>
  • To: Xml-Dev <xml-dev@ic.ac.uk>
  • Date: Tue, 17 Aug 1999 17:06:00 +0200

Jim Garrett wrote:

> Is/has anyone working/worked on a programming glue layer
> between the RDBMS and the XML doc, so that it goes both
> ways in real time.
> So that the latest and greatest is always present in the
> I need the Glue to work in both directions.
> Or are all solutions just Glue out to XML and the standard
> POST back to the RDBMS for the return trip.

XML-DBMS transfers data in both directions, using a DOM tree on the XML 
end. Whether this meets your requirement for "real time" is not clear. In 
particular, changes made in the DOM tree are not immediately reflected in 
the database or vice versa. Instead, the programmer must call a method to 
update the opposing media and the methods that do this transfer all the 
data, not just the changed data. This was an explicit design choice, as the 
software was really designed for simple data transfer.

If you are looking for immediate reflection of changes, then what you need 
is a DOM implementation directly over a relational database. Although this 
has been discussed, I'm not aware of any implementations of it. 
Furthermore, this would be far more complex to implement than data 
transfer. For example, it would require the database to notify the DOM tree 
of changes. Since this isn't covered by JDBC, the code to do it would 
probably be database-specific, if the database supported such capabilities 
at all.

Out of curiousity, if you do need immediate updates, what is your scenario? 
 Except for writing a persistent DOM with a relational database as the data 
store, I'm having trouble imagining why anybody would need this.

-- Ron Bourret

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