[DAS2] <CATEGORY> elements

[Ed Erwin]

Andrew Dalke wrote:
> One discussion point from today is the <CATEGORY> elements.
> 
> The current draft of the spec says they look like this
> 
>       <CATEGORY type="segments" query_id="volvox/1/segments">
>           <FORMAT name="fasta" mimetype="text/x-fasta" />
>           <FORMAT name="raw" mimetype="text/plain" />
>       </CATEGORY>
>       <CATEGORY type="types" query_id="volvox/1/types">
>           <FORMAT name="das2xml" mimetype="text/x-das-featuretype+xml" />
>       </CATEGORY>
>       <CATEGORY type="features" query_id="volvox/1/features">
>           <FORMAT name="das2xml" mimetype="text/x-das-type+xml" />
>       </CATEGORY>
>       <CATEGORY type="locks" query_id="volvox/1/locks" />
> 
> 
> Andreas Prlic pointed out that since the document says
> the "volvox" version "1" url is already known ("volvox/1")
> and the type="segments" then the query_id can be built
> from appending "segments" to the "volvox/1" (plus the "/")
> to get "volvox/1/segments".
> 
> I originally responded from a ReST purity argument, in that
> URLs should not be constructed from non-URL data.  This
> lets Thomas, for example, use GUIDs for the objects rather
> than the hierarchical structure I and others recommend.
> 
> During discussion a better answer came up, which I think
> we talked about earlier but which is worth emphasizing
> is that the "query_id"s don't need to be on the same server.
> 
> For example, the "regions" URL may and likely will point
> to a common reference server, and a database may offer
> only one set of "types" for all of the "features".
> 
> That is, something like this
> 
>   DAS server example.com
>      genome A
>         version x
>           segments at "ensembl.org/das2/genome_A/build_1/segments"
>           features at "example.com/A/version_x/features"
>           types at "example.com/A/types"


None of your examples vary the words "segments", "types" or "features", 
but it is legal to do so, right?:

            segments at "ensembl.org/das2/genome_A/build_1/segment"
            features at "example.com/A/version_x/things/and/more/things"
            types at "example.com/A/rhinoceros"

OK, so no one is likely to go that far, but is it legal for example to 
use non-plural "segment", "feature" and "type" ?