Re: [core] Link target attributes in CoRAL (was: Review of CoRAL)

[Christian M. Amsüss <[e-mail]>]

On Tue, Nov 13, 2018 at 02:09:02PM +0900, Jim Schaad wrote:
> > It's a trade-off, though: While making the resulting data
> > semantically > more palatable, it makes link filtering odder (a `GET
> > /.well- known/core?ol=coap://x/`  CoRAL response one'd need to think
> > `GET /.w- k/c?anchor=coap://x/&rel=attr:ol`). I still think it's
> > worth it (speaking > as someone who'll have to implement the
> > lookups).
> 
> Would a more interesting version of this end up being
> 
> GET /.well-known/core?ol=coap+tls://x/
> 
> Although I am completely unsure if that means the same thing as what you
> suggested.

Yes, that's the kind of lookups I'm thinking about.

The rel=attr:ol lookup above is not something I expect we'd ever send
over the wire, but should express the differeneces in models we are
facing: The CoRAL/RDF data model knows no attributes to look up aganist,
and could (especially with link-valued attributes) not even know from
the data alone whether something is a link or an attribute.

When implementing query filtering, one will first see

    ?ol=coap+tls://x/

then will recognize that ol is a link-valued target attribute, so the 
query is internally semantically equivalent to

    SELECT ?target WHERE { ?target attr:ol <coap+tls://x/> }

(which is a form of lookup one'd also have if a query were for
?anchor=coap+tls://x/&rel=something), and then look into the data again
to convert back.

I guess what I'm eventually saying here is that the way query filtering
is expressed is tightly bound to the web links (annotated targets)
information model, and running them against the CoRAL model (only links,
but also to literals; which I personally think is way more elegant) does
not come trivially.

It is possible, and well-defined once a mapping between the information
models, and can probably even be implemented efficiently, but not
immediately obvious when thinking in CoRAL and seeing a filter query.

Best regards
Christian

-- 
To use raw power is to make yourself infinitely vulnerable to greater powers.
  -- Bene Gesserit axiom