I would have put it under Software Development.
Personally, i think it would make sense for it to be in the software development area but at the same time, it makes sense that it is in the web development category.
Databases are pretty fundamental to both parent categories, and while I can guess why Dani put it under web development originally, our current push for tagging rather than categories means that the location becomes less important. Unfortunately, it means that in the interrim there's a bit of confusion.
Can someone please remind me - how do I filter based on one or more tags? If I click on a tag I can get a list of tagged articles, and if I do a search I can find articles containing that text, but what if I want to specify a tag manually rather than just selecting one of the few presented at the bottom of the page?