Mark Pilgrim's XFML Python library
Mark Pilgrim is writing a python library for XFML: dive into mark - xfmllib: "XFML is a new format for providing hierarchical faceted metadata. Think of it as a way of expressing all the different cross-sections of a site. I couldn't make heads or tails of it until a kind soul came along and mocked up an XFML representation of Dive Into Accessibility, my tutorial on web accessibility techniques. Then it all became clear.
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You see, each tip in Dive Into Accessibility discusses a specific technique, the general design principles the technique embodies, the types of disabilities (expressed in the form of character sketches) that would benefit from its implementation, the web browsers involved, and (in some cases) specific instructions for implementing the tip in various publishing tools.
To express this in XFML, we first define six top-level facets: person, physical disability, technological disability, design principle, web browser, and publishing tool.
Within the person facet, we define topics: Jackie, Michael, Bill, Lillian, Marcus, and also Google, since many accessibility techniques directly impact search engine placement, and Google's spidering bot can be thought of as a blind reader (a really, really voracious reader).
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Now feed it into a portal-making script and it looks like a portal. Or feed it into a search-engine-making script and it looks like a search engine. That's wicked cool."