service description vocabulary

Beyond what's currently listed in the vocab section of the service  
description page[1], I think we need a way to describe the dataset  
provided by the endpoint. This goes beyond what things like voiD  
provide which is a way to describe a single graph. Therefore, I'd like  
to suggest something like this:

<endpoint> sd:datasetDescription [
	sd:defaultGraph <void-dataset-for-default-graph> ;
	sd:namedGraph [
		sd:graphName <graph-name> ;
		sd:graphDescription <void-dataset-for-named-graph> ;
	] .
] .

The lack of naming symmetry between sd:defaultGraph (for default  
graphs) and sd:graphDescription (for named graphs) could probably be  
made better (maybe sd:defaultGraphDescription?), but this modeling  
allows each graph in the dataset to be described as well as things to  
be said about the entire dataset.

Additionally, I was hoping to get feedback on whether people think the  
vocab should distinguish between language extensions and supported  
features? Is this a meaningful distinction? For example, an extension  
that modifies the SPARQL syntax (e.g. to support the BINDINGS keyword)  
versus a feature describing the algorithm used to generate DESCRIBE  
results. The former clearly extends SPARQL, but the latter works  
within the existing constraints of SPARQL. Thoughts?

thanks,
.greg

[1] http://www.w3.org/2009/sparql/wiki/Feature:ServiceDescriptions