SquishQL  is a way to query RDF documents and has been worked out by Libby Miller. While reading down the document I came across that \”co-depiction\”  example by Dan Brickley where he writes:
The FOAF vocabulary provided a way for RDF documents to talk about people and their characteristics. FOAF documents also make use of hypertext, providing \’seeAlso\’ links to other FOAF documents elsewhere in the Web. This simple convention makes it possible for RDF indexing tools to explore an (RDF)Web of linked documents (hence the name of the project).
Now this is cool.
The co-depiction experiment grew naturally out of this. If we knew who was depicted in an image, we could explore a Web of relationships between people that were \’co-depicted\’. Two people are co-depicted if there exists some digital image that depicts them both.
I really need to spend more time on that. FOAF seems to have real potential for many applications on the web. FOAF related to blogging is probably just the beginning.