TreeHugger 0.1

1. Introduction

TreeHugger is an attempt to use xpaths and xslt on rdf graphs (a tree-hostile environment). You can download it here. Be warned that it's only been compiling for a day, so it's very pre-alpha.

TreeHugger tries to make an RDF graph look like an ideal RDF/XML serialisation. Hopefully XSLT stylesheets that 'break' when confronted by odd serialisations will convert easily to TreeHugger.

TreeHugger was written by Damian Steer. It is Free Software, released under a BSD-style licence.

2. Using TreeHugger

Before starting you should probably flick through my introduction, particularly the example. Next try the online playground, where you can try stylesheets.

If you want to play in the privacy of your own home then download treehugger. INSTALL and README should be all you need.

3. Notes

Here are a few notes on TreeHugger and XPath:

• Root corresponds to the RDF document. Its children are all the subject nodes in the graph
• Properties have a dual identity: they are elements and they are attributes, just as they may be in RDF/XML.
• Literals are (currently) text nodes. That is like RDF/XML. However that means they can't have attributes (like lang and datatype). I'll have a think about that.
• Resource elements are indicated by type (eg foaf:Person). If a resource doesn't have a type (like the object of foaf:mbox) use rdfs:Resource or rdf:Description.
• TreeHugger is pretty inefficient, dynamically creating a tree from a graph as the stylesheet requires. A much better route is creating rdf queries from XPath expressions. TreeHugger was easier to write inefficiently, however.

4. Future Development

• There are many unimplemented XPath features, but the most notable is the descendant axis (//). This could be nasty, but I'll have a go soon.
• Provide some way to connect to RDB-backed models. I need to look through the Jena documentation to find out how straightforward this is.
• DAML/OWL collection support. This must be easy. Back to Jena docs...
• Move to Saxon 7.x, which would provide XPath 2.0, XSLT 2.0 and XQuery 1.0. XQuery is probably the most tricky to hook in to.
• Cool logo?

5. Acknowledgements

• Max Froumentin and Libby Miller, who started my interest in XSLT, XPath and XQuery over RDF.
• Norm Walsh, whose RDFTwig, though pretty different, showed me how to use Saxon.
• The Saxon and Jena developers, whose code does most of the real work.

6. Related

Sean B. Palmer's Pondering RDF Path contains some useful information and links to RDF-specific path languages.