Dear Jose Maria,
Thank you for your comments. Please, see our response inlined.
> we would like to raise some questions regarding the practical use of > import clause w.r.t RDF data and OWL ontologies: > > 1) Which is the minimun set of RDF serialization formats that are > supposed to be supported by a RIF implementation? In the specification > SWC we read: > > "Several syntaxes have been proposed for the exchange of RDF graphs, the > normative syntax being RDF/XML. RIF does not provide a > format for exchanging RDF graphs; it is assumed that RDF graphs are > exchanged using RDF/XML, or any other syntax that can be used for > representing or exchanging RDF graphs."
With the text you quote, above, we are trying to provide a little guidance in an area which is architecturally independent of RIF. While we recognize that RIF implementors need to know which RDF access protocols and formats they need to support, we do not believe we are in a position to answer that for them; they have to make their own assessment of the RDF standards. We note that when RIF started, RDF/XML was the only W3C-recommended way to access RDF data; since then, SPARQL and RDFa have also become W3C Recommendations. Our expectation, which we intended to convey in the text you quote, is that systems will at least support RDF/XML, but that it is better for us not to set mandates concerning a issues in the RDF space.
> Note that the test cases use the Turtle syntax.
Thank you for pointing out this incongruity. The test cases have now been modified to use URLs which are independent of content type, and the downloadable/live test suite (not the wiki) now includes both RDF/XML and Turtle.
which is served as both RDF/XML and Turtle, depending on the HTTP "Accept" header that is used (see below). The default is RDF/XML. A suffix of .rdf or .ttl can also be appended.
> 2) If more than one RDF serialization format are to be supported or > required, how the RIF implementation can determine the parser to be used > for each import clause?
This is matter for the appropriate Web and RDF specifications. In general, with Web dereference operations the underlying protocol conveys this information. With HTTP URLs, the Content-Type header identifies the syntax the delivered content. For RDF/XML the type is "application/rdf+xml", for turtle it's "text/turtle", etc. See http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.17 and http://www.iana.org/assignments/media-types/ for more details on that mechanism.
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Sandro Hawke, in behalf of the RIF WG