hi,
I have an XML file which I'd like to query (read/write) in the same way as I would a relational database. Performance is not a big issue, I just want to be able to load the file and start querying, preferably without having to define a schema. Does anyone know if such software exists?
If you're familiar with C# and Linq, LinqPad is the way to go. You can use Linq to Sql and Linq to XML from there.
It's not a GUI, but xmllint has a shell option, which allows you to interact with XML files via XPath. It's quite handy and a little bit similar to browsing a directory structure in Unix. See http://xmlsoft.org/xmllint.html
I'm not entirely sure what you mean by read/write but assuming you want an Access-like experience, try the Oxygen XML Editor.
It's a great XML general editor with a lot of support for querying and their Grid Editor does a nice job of allowing you to just insert/delete row if there is any recurring data in the XML.
As well as XPath, it also has full XQuery support with GUI to help you write queries.
I've used it for years - I particularly like the license terms and cross-platform GUI which let me use it on any of my machines including Mac.