A while back, I wrote about the changing face of XML, and said that XML and relational databases appeared to be a slow starter. XML database guru Ron Bourret wrote back with a different perspective.
Here's what he has to say:
I've been off wandering about the Web tonight and ran across the following statement on your blog:"Databases. Though there's a reasonable amount of interest in the W3C XML Query language, there's not much to say about XML and databases. It doesn't seem to me that the integration of XML with relational databases has taken off in the way we once thought it might."
I will admit to just a wee bit of bias here, but I'm not sure I'd translate a lack of conference presentations to the integration of XML and relational databases not taking off. The use of Web services has certainly taken off, and I'd venture to say that behind almost every Web service is a relational database generating or receiving data in XML form.
On the other hand, the lack of conference papers seems indicative of what's going on in the XML database industry:
1) The basic mappings between XML and relational databases are around five years old and haven't changed much in that time. Hence, there's not a lot to talk about at conferences, at least in terms of cutting edge stuff.
2) SQL/XML is somewhat new and Jim Melton seems to be a fixture at most conferences, but he's just one guy and doesn't translate into more than one talk. Although it is supported by DB2 and Oracle, SQL/XML suffers from a less than wonderful surface syntax. I have no idea how widely it is used -- the Web is almost devoid of information about it -- but if I was using DB2 or Oracle and needed to publish my data as XML, I'd use SQL/XML. There aren't really any other competitors with the same degree of flexibility.
3) XQuery over relational databases hasn't taken off like I thought it would. IBM came out with an alphaWorks product a year or two ago, but it doesn't appear to have gone anywhere since. There are also a number of integration products that do this and new ones seem to be showing up slowly but steadily, but the authors don't seem to do conference presentations. From a conference point of view, XQuery-over-relational seems to be one slide in an XQuery presentation.
4) The big relational databases do seem to have some exciting things in the works, but what they're doing is mostly implementation of existing ideas (e.g. XQuery, SQL/XML) rather than pushing any new boundaries.
Yukon (SQL Server) is due out in 2005 and claims to have native XML support -- that is, the XML data type is supported by what appears to be a native XML database built into the relational database. If this is true, it's significant. They also have an XQuery implementation and can query relational data from XQuery as well as embedding XQuery queries in SQL. Good stuff.
Oracle 9i release 2 was the first out with "native" XML support, but their "native" XML support means storing the XML in a CLOB column or mapping it to relational columns with an object-relational mapping, with XPath supported over both types of storage. The CLOB support is is cute, but it won't scale without heavy indexing. Oracle has an XQuery prototype with extensions for SQL queries inside XQuery. It appears that this works over both the aforementioned storage types, but I'm not really sure. If they add true native storage, this will be a good product.
DB2 currently has SQL/XML support and they had the first XQuery-over-relational implementation, although only on alphaWorks. They haven't said much publicly about where they are going with XML support, but given the amount of work going on in their labs, one assumes some of it will eventually make it into DB2.
Sybase, Informix, Access, and FoxPro have XML support as well, but I haven't tracked these closely enough to know where they're going in the future. (Oddly enough, Sybase provides native XML storage, but not much in the way of XML support for existing data.) One of the great mysteries to me is why PostgreSQL and MySQL essentially don't have XML support. They've got some toy stuff, but nothing serious. Maybe Open Source middleware is filling the need?
My guess is that everything will pick up on this front in a year or two, with companies moving towards what I consider the holy grail of XML support in relational databases: native storage behind a first-class XML data type, XQuery support with extensions for (a) including relational data or SQL queries and (b) updates, SQL/XML support with extensions for embedded XQuery queries, and support for JSR 225 (see below).
Of course, this still won't translate into lots of conference talks, as only a few companies are involved.
5) IBM and Oracle are leading work on a Java API for XQuery (JSR 225), but this isn't strictly for use with relational databases. Still, it should start showing up at conferences at some point in the near future.
6) Native XML databases commonly include the ability to integrate data from relational databases. (There are a number of XQuery-based integration engines that work with relational and other types of data as well.) You can find a number of these companies on the trade-show floor at conferences but, except for Mike Champion from Software AG, few of them seem to do presentations.
I beat up the native XML database companies on this every chance I get, but I haven't seemed to make much headway. Not sure if this is lack of budget -- except for Software AG and Sonic (eXcelon), these companies tend to be small -- or just that they're making the mistake of a lot of technology firms that technology trumps marketing. (Which, of course, explains the failure of Microsoft in the marketplace ;) That said, the number of presentations by these companies at conferences has gone from zero a few years ago to a few now.
Edd Dumbill is co-chair of the O'Reilly Open Source Convention. He is also chair of the XTech web technology conference. Edd conceived and developed Expectnation, a hosted service for organizing and producing conferences. Edd has also been Managing Editor for XML.com, a Debian developer, and GNOME contributor. He writes a blog called Behind the Times.
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