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Re: SPARQL syntax proposals

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Sat, 05 Mar 2005 15:09:54 +0000
Message-ID: <4229CBC2.1070908@hp.com>
To: Eric Prud'hommeaux <eric@w3.org>
Cc: public-rdf-dawg@w3.org



Eric Prud'hommeaux wrote:
> On Tuesday, the DAWG f2f took up syntax issues. We came up with a
> syntax that was acceptable to all or most (don't know how SteveH would
> phrase his feelings) of the attendees. These are expressed as examples
> below. The principal change was in expressing the graph pattern in
> "turtle+variables". Afterwords, Andy, Steve and I worked out how to
> express regexps and not get an inscrutable grammar like perls.
> 
> We also changed AND to FILTER to express some constraints that we had
> put on the effect of the value constraints section (namely that this
> section ONLY restrict results, never add results or even, I think,
> produce variables bindings).
> 
> These examples give a pretty good idea of our ideas:
> 
> simple query:
> SELECT * WHERE { ?p ?s ?o }
> 
> 
> which prefix:
> PREFIX foaf: <http://example/foaf#>
> SELECT ?me ?you
>  WHERE { ?me foaf:knows ?you. ?you foaf:knows <fred> }
> 
> could also have either of these forms:
>  WHERE { ?me rdf:type foaf:Person.} # trailing thingy in lexer
>  WHERE { ?me rdf:type foaf:Person .} # parses same as above
> 
> 
> ex with GRAPH and '.' in (but not ending) a QName.
>  WHERE { GRAPH ?g  { ?g dc:source myPartOfUriSpace:foo.rdf } }
> this is like turtle but n3 does not currenlty allow '.'s in names.
> 
> 
> use the same syntax in the CONSTRUCT graph:
> PREFIX foo: <http://www.w3.org/>
> CONSTRUCT { ?s foo:bop ?o2 .
>             ?o2 foo:bing ?o }
> WHERE { ?s foo:bar ?o .
>         ?o foo:baz ?o2 }
> 
> use turtle list syntax;
>  WHERE { :bob :brothers (:joe :sam) }

Presumably lists can be nested.  ( 1 ( 2 3 ) 4 )
and the rd;type rdf:List is not needed.

- - - - - - - -

What about this one:

   SELECT * WHERE { ( ?x ) }

because a list is just some triples.  It's the same query as:

SELECT  *
WHERE
     { _:b rdf:first ?x .
       _:b rdf:rest  rdf:nil .
     }

"find all the elements at the end of a list".


Looking around:
cwm 1.0.0, parsing the file:
--------------
( 1 ) .
--------------
generates an empty model without warning or error.

Jena parses that input as the triples:
-----------------
@prefix rdf:     <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

_:b1      rdf:first  1 .
_:b1      rdf:rest  () .
-----------------

Turtle allows lists only as blank nodes in other triples, not free standing 
triples.

The difference in grammar terms is small - just whether a list can be seen 
in place of a triple or not.

   triples  ::=   subject predicate-object-list
                |
                  collection

or

   triples  ::=   subject predicate-object-list


	Andy

> 
> use turtle ';' operator:
>  WHERE { ?doc dc:title ?txt; dc:author ?who }
> (good for symmetry even if not often used in queries.)
> 
> use turtle ',' operator:
>  WHERE { ?who foaf:knows ?f1, ?f2 }.
> (?who knows ?f1 and ?who knows ?f2.)
> 
> turtle has the 'a' operator (shortcut for rdf:type)
>  WHERE { ?who a foaf:Person } # yes
> but not other operators like '='.
> 
> bNodes are interpreted as unique, unreferencable variables.
> SELECT ?who WHERE { ?who :brother [ in Army ], :mother [ in Navy] . }
> (same as            ?who :brother ?b. 
>                     ?b in Army.
>                     ?who :mother ?m.
>                     ?m in Navy              )
> 
> as promised, AND is now FILTER:
> SELECT ?who
>  WHERE { ?who :age ?n. FILTER ?n + 1 < 5 }
> 
> 
> The promised the regexp syntax:
> 
> regexp(?x , "regexp"[, "flags"])
Received on Saturday, 5 March 2005 15:11:05 GMT

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