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There's also PostgreSQL =)

Yes, commercial databases with an Open Source tag are not your only option.

Absolutely, dzonelurker, but there are those who like the assurance of an available option for paid support from a world-class player like Big Blue. I can understand the appeal of that as an upgrade option, and if I read correctly this is actually free. If it works for MySQL and EnterpriseDB (warmed over PostgreSQL?), then why not DB2 as well?

You bet DB2 Express-C is free. It is actually "more free" than MySQL if such thing is possible. MySQL can be used for development and use in production for both non-commercial and commercial applications. But if you want to redistribute it for commercial purposes you have to sign an OEM agreement with MySQL. With DB2 Express-C you can actually redistribute the database as part of your application without paying IBM any money. All you need to do is tell IBM how you plan to use it. Nothing to pay. I am not trying to say that MySQL is bad or not worth consideration. It is pretty decent for what it is designed to do. DB2 Express-C brings a lot of things to a developer that MySQL does not. Things like hybrid relational-XML database engine, or complete indemnification so you don't get sued by someone who all of a sudden wants to partake in your success and a bunch of other things.

I just started a new blog on DB2 Express-C at FreeDB2.com. Come check it out.

There's also SQLServer 2005 Express and Oracle has some free versions too.

Let me say, I am not affiliated with IBM at all, but I've been using DB2 for about 8 years and I have deployed several applications using DB2 ESE as well as their DB2 Express-C offering.

The pureXml functionality provided in DB2 9.5 is actually pretty amazing. XML data can be stored (and indexed) with an XML type. You can also run XPath inquiries against multiple xml documents and obtain the results as a set .

Think about it like this:
Given a table containing two rows with a column containing XML data:
Row1: <root><val><1></val><val<>2</val/rootrootval/valval/val/root<

You can write a single SQL query (which contains a bit of XPath) to give you the following set:
1
2
3
4

On a completely different note, DB2's Express edition doesn't have a 4GB storage limit like SQL Server 2005 Express. The primary limitation on this version of DB2 is that it will only utilize up to 2 Dual-core CPUs and 4 GB of RAM.

Darnit. DZone ate my XML. Please use the XML provided here

Row1:<root><val>1</val><val>2</val></root>
Row2:<root><val>3</val><val>4</val></root>

Sorry, Scott. Maybe we can integrate the TinyMCE and dp.SyntaxHighlighter support we have used in the new Zones sites. It woul dbe great to be able to have highlighted code in comments here, too.

pureXML means that XML is stored in it's native tree structure, like native XML databases store XMLs. XML type is known for quite some time, but DB2 is the first to store it in it's native tree structure, other databases use shredders for that, meaning they store the data into relational tables and when you need the XMl document they build it again.
I hope I made some sense. :))

And yes, you can intermix SQL and XQuery in single statement. :))

IBM has had this Express version of DB2 since a while ago which is a good thing. Options are always welcome in our programming world but when it comes to comparing DB2 to MySQL there's a different story. I work with them both and I can say that I like MySQL better because of it's simplicity and ease of use. Performance wise, DB2 is a little more solid than MySQL but I guess that depends on the hardware they run also, and I did not get the chance to see them run in the same conditions.

I think that DB2 Express-C is the best of the free versions of the major commercial DBMS'es. It's easier to use than Oracle...

Oracle XE's been free for some time. Full-fledged Oracle code base up to 4GB of user data. http://www.oracle.com/technology/products/database/xe/index.html. Actually javacrawl.com is now running on Oracle XE.
,

Yeap, Oracle XE is free and I actually do like it more than the paid versions of Oracle database. However, with a 4GB hard limit a maximum of one processor and, the ridiculously low 1GB of memory limit it is by no means a match for DB2 Express-C.