(Rob Sanderson, member of Biblio project, main editor for SRW, University of Liverpool, Computer Science Dept)
The main issue, in my opinion, is one of abstraction (isn't it always?)
We do not want the end user to have to understand the incredibly complex table structure required to implement MODS in SQL. We do not even want the -developers- to have to understand this. Instead we want to be able to use off the shelf, easy to understand technology to get records in XML, save them and later perform operations on them.
This is easiest to accomplish using an XML record store system rather than constantly shredding the document into SQL tables and rebuilding it.
In the information retrieval world, the current standard protocol for remote search and retrieve of any XML documents is SRW. The query language for SRW is abstract (called CQL) -- for example you use an abstract 'title' search rather than XQuery's syntax specific approach.
For the purposes of the Bibliographic project, the entire Library of Congress database is available in MODS format for free via SRW/CQL.
If we download and store those records in a relational table of any complexity, then every time there is a change to the schema, the tables need to be rebuilt. This would consume a lot of time and effort, rather than possibly having to change an XPath value.
The only thing that is certain in this world is change.
To use an OOo centric example, if documents were stored in a relational database and an element's content model in the schema changed, we would have a nightmare situation. In an XML database with appropriate schema version metadata, this is almost trivial.
Hope this makes sense,
-- Rob Sanderson
,'/:. Dr Robert Sanderson ([EMAIL PROTECTED]) ,'-/::::. http://www.o-r-g.org/~azaroth/ ,'--/::(@)::. Dept. of Computer Science, Room 805 ,'---/::::::::::. University of Liverpool ____/:::::::::::::. L5R Shop: http://www.cardsnotwords.com/ I L L U M I N A T I
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