xml-dev - Re: XML data bases, document management

["Ronald Bourret" <rpbourret@hotmail.com>]

>does anybody have practical experiences with XML data bases? like e.g.
>poet, objectstore or tamino? what do you think about them? can you
>recommend a product in this area?
>
>i want to setup a document management system based on such a data base,
>therefore i'm interested in pointers to already existing applications.

Here's two links you might be interested in:

http://www.informatik.tu-darmstadt.de/DVS1/staff/bourret/xml/XMLAndDatabases.htm

http://www.informatik.tu-darmstadt.de/DVS1/staff/bourret/xml/XMLDatabaseProds.htm

The first is a paper I've written (XML and Databases) explaining the basic 
concepts behind using XML with databases. The second is a pretty 
comprehensive list of products for using XML with databases -- from 
middleware to XML databases to document management systems.

If you're interested in writing a document management system, then you 
should look pretty closely at exactly how any of these products saves an XML 
document in a database. I'm not sure about the XML databases such as those 
you mention, but most of the middleware for working with XML and databases 
probably isn't adequate for your needs. This is because such products, as 
well as XML-enabled databases like Oracle and DB2, tend to concentrate on 
transferring the data (as opposed to document structure) from an XML 
document to the database and vice versa.

In particular, you will probably want to preserve the following information 
in the database:

   Elements and attributes (obviously)
   Hierarchical structure (obviously)
   PCDATA in mixed content
   Order of sibling elements
   Order of values in multi-valued attributes
   Entity and character references
   CDATA usage
   Processing instructions
   DTDs
   etc.

In addition, you will need the following capabilities:

   Bidirectional transfer
   The ability to model arbitrary (any) XML documents
   Update and delete of existing documents

My guess is that these requirements are going to wipe most existing 
XML/database products off the list. In particular, most of the available 
middleware has very limited abilities to model arbitrary XML documents and 
I'm not aware of any that preserves physical structure, such as entity and 
CDATA usage.

The XML-enabled databases (such as Oracle, DB2, etc.) generally do a better 
job of modeling arbitrary XML documents, although whether they can model 
*any* XML document is not clear to me. Similarly, I would be surprised if 
they stored physical structure information or could handle things like PIs 
and DTDs.

Unfortunately, I don't know much about the so-called "native" XML databases 
like Tamino, but these might have a better chance of meeting your needs. 
Again, it depends on whether they are designed to handle data or document 
structure.

My best guess is that you will want to use a persistent DOM implementation, 
such as that from GMD (http://xml.darmstadt.gmd.de/xql/index.html), or roll 
your own.

-- Ron Bourret
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