xml-dev - Re: Relational Tables and structured document

["G. David Kuhlman" <dkuhlman@netcom.com>]

I've been following the comments about using XML as a database, and
I have a question -- The discussion of ODMG and using XML as a
database suggests that you will be able to update the database. 
But, if you have a large XML file, how do you update fields within
that file without copying or re-writting the whole file?  That
sounds very awkward.

Or am I missing a step in this process?  Are we assuming that the
XML file has been sucked into an OODBMS such as one for which there
are ODMG language bindings?  I think this would be very powerful. 
However, it is no longer XML, is it?  Or is the goal to store the
data in a RDBMS or OODBMS and then export it to XML so we can send
it across the wire and around the Web?

I guess I am asking whether there is a model this kind of use of
XML as a database.

Dave



> Peter Murray-Rust:
> 
> >I have been spending the last two weeks working on a molecular application
> >which essentially consists of relational tables.  The application is
> >largely hierarchical (a protein molecule) so that it benefits from being
> >recast into structured document form. I have therefore found it useful to
> >create routines which generate nodes in a tree as a result of joining
> tables.
> 
> 
> I think there are several things that one could usefully do.
> 
> (1) define a recommended way of representing a relational table in XML.
> (There
> are a number of ways of doing this, the biggest decision is whether to use a
> standard DTD for all tables or a DTD that reflects the specific table
> definition.)
> 
> (2) extend this to a richer data model, e.g. the nested relational model,
> that
> allows you to represent hierarchic structures, or the ODMG model which
> allows
> to to represent arbitrary graphs. (Note that the problem then becomes
> analogous to the one of using XML as a serialisation format for CORBA
> objects)
> 
> (3) provide a toolkit that allows you to perform transformations on these
> XML
> documents that reflect the operators of the relevant data model, e.g.
> relational
> selection, projection, and join; sorting and grouping; flattening of nested
> relations.
> Of course one way to implement such operations would be to load the data
> into
> a database, but many of the operations can be implemented directly without
> too
> much effort.
> 
> I think the key thing is to keep the set of structures and operations very
> clean:
> base it on a data model with an established formal basis rather than
> inventing
> something new.
> 
> Mike Kay, ICL
> 
> 
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