[xquery-talk] Re: The State of Native XML databases

[Michael Kay]

> Why can't a document in the collection just become 
> a node of a node collection within a schema bound storage?

We did look at the idea of making a collection into another kind of node
above the document node level. However, we felt this might be
institutionalizing the concept of a collection rather prematurely. It would
force one to answer all sorts of questions such as whether a document can
belong to more than one collection, whether collections can contain further
collections, whether there is any relationship between the URI of a
collection and the URIs of the documents within it, whether the documents in
a collection have any stable ordering. We felt it was probably better to
keep collection as a lightweight abstraction with a lot of implementation
flexibility and see how implementations ended up taking advantage of it.

This extends to the relationship between collections and schemas. Current
products are handling this in a wide variety of different ways, none of
which is yet provably the best way. So standardisation would be premature.

The concept of the database as a single-level XML hierarchy with a single
database node at the top is attractive intellectually, but for many
practical applications the concept of a database as a flat collection
containing a large number of moderate-sized documents is a more manageable
proposition. Certainly I think the engineering is better understood. 

Michael Kay
http://www.saxonica.com/