[xquery-talk] Comparing XML Databases to Object Databases

Michael Kay mike at saxonica.com
Wed Mar 19 12:15:08 PST 2008

The database market is incredibly conservative and risk-averse, both in
relation to new technologies and new suppliers. MySQL and PostgreSQL have
shown that you can break the mould in terms of suppliers (but only by
cutting the price to zero), but no one has yet proved it in terms of

The advantage of going with a hybrid database is that you are effectively
deferring a decision on your technical direction, which makes it an easier
decision. The disadvantage is that you end up leaving junior programmers to
make the real technical decisions on a case-by-case basis, and they will (a)
get it wrong half the time, and (b) fight with each other over which way is
best [yes, I've watched this happening, and it's painful]. But that argument
won't sway decision-makers who think they can have their cake and eat it,
and who often have a dismissive attitude to arguments based on technology

The biggest weakness in the object database market was standards. The
companies collaborated on ODMG, but they implemented different parts of it
and the products were never interoperable. Also, the technical architecture
was a bit of a mess - because of the focus on persistent C++, you ended up
with a navigational DML and a query language that bore very little
relationship to each other, and with applications that were very closely
tied to the physical data structure. So unless you needed the raw speed, for
example in CAD applications, there were few benefits. I think that the XML
database scene is very much better served in this respect.

But however good the technical merits, there's no doubt that XML databases
have an uphill struggle convincing corporate decision-makers, especially
when the Oracle/DB2/Microsoft sales people are saying "we can do it too, you
don't need to take any risks, you don't even have to decide yet what your
technical direction is going to be." Many people prefer to stick with the
devil they know. Some don't even recognize that they are dealing with the

Michael Kay

> -----Original Message-----
> From: talk-bounces at x-query.com 
> [mailto:talk-bounces at x-query.com] On Behalf Of John Snelson
> Sent: 19 March 2008 11:29
> To: talk at x-query.com
> Subject: [xquery-talk] Comparing XML Databases to Object Databases
> I had a conversation the other day where XML databases were 
> being compared to object databases. The person I was talking 
> to suggested that it was inevitable that XML databases would 
> get subsumed by the existing RDBMSs on the market, just like 
> object databases had been.
> I haven't had the benefit of experiencing the rise and fall 
> of object databases, but I have some opinions as to why I 
> think XML databases have a better chance than object 
> databases ever had. What does everyone think? Are XML 
> databases headed for obscurity, or is the time for them right 
> and the comparison to object databases unfounded?
> John
> -- 
> John Snelson, Oracle Corporation            http://snelson.org.uk/john
> Berkeley DB XML:        http://www.oracle.com/database/berkeley-db/xml
> XQilla:                                  http://xqilla.sourceforge.net
> _______________________________________________
> talk at x-query.com
> http://x-query.com/mailman/listinfo/talk

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