A couple of weeks ago, I've written about the self-enforcing value spiral that RDF data enables. Here is an example about how RDFa can be used to support this "Repurpose-Republish" loop.
While data exchange between different semantic web sources is usually RDF-based (i.e. the data always maintain their semantics), there is one major exception: SPARQL SELECT queries. This developer-oriented operation returns tabular data (similar to record sets in SQL). Once the query result is separated from the query, the associated structural data is lost. You can't directly feed SELECT results back into a triple store, even though querying based on linked resources means that you have just created knowledge. It's a pity to show this generated information to human consumers only.
One of the demos at my NYC talk was a dynamic wiki item that pulled in competitor information from Semantic CrunchBase and injected that into a page template as HTML. The existing RDF infrastructure does not let me cache the SELECT results locally as usable RDF. And a semantic web client or crawler that indexes the wiki page will not learn how the described resource (e.g. Twitter) is related to the remote, linked entities.
However, by simply adding a single RDFa hook to the wiki item template, the RDF relation (e.g. competitor) can be made available again to apps that process my site content. This is basically how Linked Data works. But here is the really nifty thing: My site can be a consumer of its own pages, too, recursively enriching its own data.
I tweaked the wiki script which now works like this: When the page is saved, a first operation updates the wiki markup in the page's graph (i.e. the not-yet-populated template). In a second step, the page URL is retrieved via HTTP. This will return HTML with RDFa-encoded remote data, which is then parsed by ARC, and finally added to the same graph. We end up with a graph that does not only contain the wiki markup, but also the RDFized information that was integrated from remote sites. After adding this graph to the RDF store, we can use a local query to generate the page and occasionally reset the graph to enable copy-by-reference. And all this without any custom API code.
How to use RDFa to make SELECT results locally available as RDF
Posted on 2009-05-26 at 07:50 UTC by trackback)(
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