Ben Adida notes that people are writing about RDFa, which is great, and envisioning conflict with microformats, which is not. As Ben says:
Microformats are useful for expressing a few, common, well-defined vocabularies. RDFa is useful for letting publishers mix and match any vocabularies they choose. Both are useful.
In other words RDFa is a long tail technology.
Evan Prodromou thinks the future is bleak without cooperation. I like his proposed way forward (strikeout added for obvious reasons):
- RDFa gets acknowledged and embraced by microformats.org as the future of semantic-data-in-XHTML
- The RDFa group makes an effort to encompass existing microformats with a minimum of changes
- microformats.org leaders join in on the RDFa authorship process
- microformats.org becomes a focus for developing real-world RDF
I see little chance of points one and three occuring. However, I don’t see this as a particularly bad thing. Point three will occur, almost by default: the simplest and most widely deployed microformats (e.g., reltag, relnofollow and rellicense) are also valid RDFa — the predicate (e.g., tag, nofollow, license) appearing in the default namespace to a RDFa application. More complex microformats may be handled by hGRDDL, which is no big deal as a microformat-aware application needs to parse each microformat it cares about anyway. From an RDF perspective any well-crafted metadata is a plus (and the microformats group do very careful work) as RDF’s killer app is integrating heterogenous data sources.
From a microformats perspecitve RDFa might well be ignored. While transformation of any microformat to RDF is relatively straightforward, transformation of RDF (which is a model, not a format) to microformats is nonsensical (well, I suppose the endpoint of such a transformation could be xoxo, though I’m not sure what the point would be). Microformats, probably wisely, is not reinventing RDF (as many do, usually badly).
So why would RDFa be of interest to developers? In a word, laziness. There is no process to follow for developing an RDF vocabulary (ironic), you can freely reuse existing vocabularies and tools, not write your own parsers, and trust that really smart people are figuring out the hard stuff for you (I believe the formal background of the Semantic Web is a long-term win). Or you might just want to, as Ben says “express metadata about other documents (embedded images)” which is trivial for RDF as images have URIs.
Addendum 20060601: The “simplest” microformats mentioned above have a name: elemental microformats.