Re: status of patch

* Sandro Hawke <sandro@w3.org> [2014-04-16 23:48-0400]
> The basic resources we produced before we set PATCH aside:
> 
>    https://www.w3.org/2012/ldp/wiki/LDP_PATCH_Proposals
>    https://www.w3.org/2001/sw/wiki/PatchRequirements
> 
> 
> Why I gave up:
> 
>    For my applications, I can't set aside the first two "general
>    requirements",  Universality (patching any graph to any graph) and
>    Tractability.  But I saw no way to meet them while still being
>    standards compliant.
> 
> Why I said we could solve this in half an hour:
> 
>    Because I know how to meet them now.   Use "Virtual Skolemization",
>    where graphs with bnodes *appear* to be Skolemized when accessed via
>    the patch-specific media type(s).    I updated TurtlePatch to use
>    this technique (although it's not explained perfectly).
> 
> Talking to Alexandre, today, it became clear his requirements are
> different.  He doesn't care about Universality, so he has lots of
> other options.   And given that, he finds the Skolemization thing
> too painful/ugly.  And it is, if you don't happen to need it.

The Skolemization approach offers great power at great expense. The
SPARQL approach offers great power at potentially great inefficiency.
My bet is that the SPARQL with constant predicates will work for 99%
of our use cases. 

I don't know if SPARQL_patch (a strict sublanguage of SPARQL) is still
on the table, but here's a yacker grammar for it:
<http://www.w3.org/2005/01/yacker/uploads/SPARQL_patch/bnf>.

It validates <http://w3.org/brief/MzYz> this example patch:

eric@mouni:~/checkouts/SWObjects$ ./bin/sparql -d 'data:text/turtle,
  PREFIX foaf: <http://xmlns.com/foaf/0.1/>
  <alice> foaf:mbox <mailto:alice@example.org> .
  <bob> foaf:mbox <mailto:bob@example.org> .
  <eve> foaf:mbox <mailto:eve@example.org> .
  <sue> foaf:mbox <mailto:sue@example.org> .
  <bob> foaf:knows <alice> .
' -e '
  PREFIX foaf: <http://xmlns.com/foaf/0.1/>
  DELETE { ?bob foaf:knows ?alice }
  INSERT { ?bob foaf:knows ?eve ; foaf:trusts ?eve }
   WHERE {
      ?bob foaf:knows ?alice .
      ?alice foaf:mbox <mailto:alice@example.org> .
      ?eve foaf:mbox <mailto:eve@example.org>
  }
' -l turtle
<alice> <http://xmlns.com/foaf/0.1/mbox> <mailto:alice@example.org> .
<bob> <http://xmlns.com/foaf/0.1/mbox> <mailto:bob@example.org> .
<eve> <http://xmlns.com/foaf/0.1/mbox> <mailto:eve@example.org> .
<sue> <http://xmlns.com/foaf/0.1/mbox> <mailto:sue@example.org> .
<bob> <http://xmlns.com/foaf/0.1/knows> <eve> .
<bob> <http://xmlns.com/foaf/0.1/trusts> <eve> .


(Uh oh, looks like eve is up to her old tricks again.)

I picked this example because it's been the principle argument for
skolemization (aka "told BNodes" or "bnodeRef"
<http://www.w3.org/2001/sw/DataAccess/issues#bnodeRef>). One can
minimize the search space by starting with the triples with the most
constants (i.e. foaf:mbox), but the search space can indeed get large
if you have a long string of ?A knows ?B. IMO, that's a small cost
compared to that of deploying solemnization.

Note that this update also qualifies as a "nailed" patch in that
replacing the DELETE… INSERT… with SELECT * yields:
┌─────────┬───────┬───────┐
│ ?alice  │ ?bob  │ ?eve  │
│ <alice> │ <bob> │ <eve> │
└─────────┴───────┴───────┘



>         -- Sandro
> 
> 

-- 
-ericP

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