IBM developerWorks has done well to corral Elliotte Rusty Harold for a column, Managing XML data, on tools and techniques for working with large collections of XML documents. The first article prepares the overall topic, summarizing likely subtopics and examining some history.
It's as good an opening as any for me to plug my own developerWorks article "Manage XML collections with XAPI". XAPI is a simple but well-considered community spec for XML database collection API.
Elliotte is one of the best writers for explaining XML technologies, right up there with Jeni Tennison. I think developerWorks is a greatly overlooked source of great materials on XML and other technologies. Maybe I'm biased because I write a great deal for them, but they also feature a lot of other very good writers and I you'd do well to check the site regularly, especially the XML zone, run very diligently by John Swanson.