XML schema for metadata: best practices ?

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HiI'm developing an metadata information architecture for "record managementsystem" running on SQL database. Records (documents) are stored in commercialdatabase (<!-- w --><a class="postlink" href="http://www.ringtailsolutions.com">www.ringtailsolutions.com</a><!-- w -->) using fixed data model, which is howeverok, since allows extensions using generalized approach (extra table containscolumuns for: label , value, datatype).We have committed to use XML for data transfer from "data collecting devices/service providers) to database. In the first phase we are using DTD for schemabut as soon as tools are mature enough will move to using W3C Shcema (strongdatatype validation etc.)Metada records are not going to be created by hand, probably as export fromservice provider's own database or using easy to use GUI tool capturing dataeventually in XML. So, it's a kind of machine to machine communication transactions.Finally the question, does anybody has recommendations for DTD/schema designconsidering creating "a SQL database friendly and maintainable metadata model"? <item> element is used to provide a extendablecontainer for arbitrary needs.Current approach has been using a unified method stroring data. All the datais stored in attributes. Elements used as logical containers.Thanks, Heimo HanninenFollowing is a fictional snippet based on the current DTD:<?xml version="1.0"?><!DOCTYPE meta SYSTEM "nested-model.dtd"><meta><record><core><data><IDcode value=http://forums.devx.com/archive/index.php/"abce0002"/><parentID value="series-0001"/><relevancy value="yes"/><status value="active"/></data><source><area value="headquarter"/><location value="credenza"/><fileName value="back up tape, all users June 23 2001"/></source><tombstone><author><person title="Mr." givenName="Peter" initials="G" surname="Pan" position="Itsupport guy" email="[email protected]" postalCity="City" streetAddress="223Queen Street"/></author><type other="backup tape"/><physicalMedia value="tape"/></tombstone><subject><description value="30 GB of user's back up files"/><classification value=http://forums.devx.com/archive/index.php/"protected.A"/><disclosure value="confidential"/></subject></core><extra><item label="trueCopy" type="boolean" value="no"/><item label="work-note" value="this will take 200 man hours to examine"type="text"/></extra><referenceList><reference><locationInfo value="room2/cabin-C34/shelf4/tape-abce0002"/></reference></referenceList></record></meta>