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[OK?] Re: Comments on SPARQL WD

From: Eric Prud'hommeaux <eric@w3.org>
Date: Mon, 23 Apr 2007 16:10:30 -0700
To: "Seaborne, Andy" <andy.seaborne@hp.com>
Cc: Olivier.Corby@sophia.inria.fr, public-rdf-dawg-comments@w3.org
Message-ID: <20070423231030.GA14194@w3.org>
* Seaborne, Andy <andy.seaborne@hp.com> [2007-04-07 18:36+0100]
> 
> 
> 
> Olivier.Corby@sophia.inria.fr wrote:
> >Hi,
> >
> >Here are some comments on current SPARQL WD.
> >
> >Best regards,
> >
> >Olivier
> >
> 
> Olivier - many thanks for the comprehensive review.
> 
> Responses and corrections done are noted inline.
> 
> Changes made to editors' working draft at:
> http://www.w3.org/2001/sw/DataAccess/rq23/rq25.html v1.80
> 
> One comment remain (11.4.10 RDFterm-equal about use of xsd:dateTime in the 
> example).  I'll defer to Eric on that one.
> 
> >2.3.2 Matching Numeric Types
> >
> >
> >SELECT ?v WHERE { ?v ?p 42 }
> >v
> ><http://example.org/ns#x>
> >
> >should be:
> >
> ><http://example.org/ns#y>
> >
> 
> Corrected
> 
> >
> >
> >2.3.3 Matching Arbitrary Datatypes
> >
> >The following query has a solution with variable v bound to :y.
> >
> >should be: bound to :z.
> >
> >
> >SELECT ?v WHERE { ?v ?p
> >"abc"^^<http://example.org/datatype#specialDatatype> }
> >v
> ><http://example.org/ns#y>
> >
> >should be :
> >
> ><http://example.org/ns#z>
> >
> >
> 
> Corrected *2
> 
> >
> >
> >2.5 Building RDF Graphs
> >
> >The SELECT query form returns tabular information.
> >
> >Could be:
> >
> >The SELECT query form returns variable bindings.
> >
> >[[Because we may exploit the results through an API and hence there may be
> >no tabular form]].
> 
> Corrected
> 
> >
> >3.3 Other Term Constraints
> >
> >
> >xsd:strings, xsd:booleans and xsd:dateTimes
> >
> >[[It look strange to add an 's' to the xsd datatype names]]
> 
> reworded as "SPARQL supports types xsd:string, xsd:boolean and xsd:dateTime"
> 
> >
> >
> >
> >4.1.1 Syntax for IRIs
> >
> >behavoir -> behavior
> Done
> 
> >
> >prefixedname -> prefixed name
> >
> Done
> 
> >4.2.3 RDF Collections
> >
> >[[Suggestion : the (1 ?x 3 4) notation for rdf list could not generate the
> >_:b rdf:rest rdf:nil triple; in such a way we could match lists that may
> >have more elements.]]
> 
> The syntax of SPARQL triple patterns, and in particular of the syntactic
> sugar forms given in section 4.2 (
> http://www.w3.org/TR/rdf-sparql-query/#QSynTriples ), is designed to be
> consistent with the syntax of Turtle (
> http://www.dajobe.org/2004/01/turtle/ ). In Turtle, the (1 2 3) syntax
> specifies a closed collection (i.e. one terminated by an rdf:nil triple),
> and SPARQL adopts this meaning for this bit of syntax.
> 
> You can match a subset of a collection by explicitly including
> the component pieces of the collection explicitly:
> 
>     _:b0  rdf:first  1 ;
>           rdf:rest   _:b1 .
>     _:b1  rdf:first  ?x ;
>           rdf:rest   _:b2 .
>     _:b2  rdf:first  3 ;
>           rdf:rest   _:b3 .
>     _:b3  rdf:first  4 .
> 
> >
> >
> >5.2.2 Scope of Filters
> >
> >A constraint, expressed by the keyword FILTER, is a restriction on
> >solutions over the whole group in which the filter appears.
> >
> >[[What happens if a variable in the filter is not bound in the current
> >group, but is bound in another group  after current group? Does the filter
> >fail? ]]
> 
> As per the text you've cited and the algebra given in Section 12, Filters
> are evaluated in terms of the solution mappings of the group in which the
> filter appears. If a variable in the filter is unbound in a solution
> mapping, then as per Section 11.2 any function or operator (except
> bound()) on the variable produces a type error. If this propagates to the
> top of the filter, then the solution is removed from the multiset of
> solution mappings.
> 
> >
> >
> >7 Matching Alternatives
> >
> >The UNION pattern combines graph patterns; each alternative possibility
> >can contain more one triple pattern:
> >
> >-> more than one triple pattern:
> 
> Done
> 
> >
> >9.1 ORDER BY
> >
> >Using ORDER BY on a solution sequence for a CONSTRUCT or DESCRIBE query
> >has no direct effect because only SELECT returns a sequence of results.
> >
> >[[
> >This is in contradiction with :
> >
> >10.2.3 Solution Modifiers and CONSTRUCT
> >The solution modifiers of a query affect the results of a CONSTRUCT query.
> >In this example, the output graph from the CONSTRUCT template is formed
> >from just two of the solutions from graph pattern matching. The query
> >outputs a graph with the names of the people with the top two sites, rated
> >by hits.
> >]]
> 
> The next sentence in 9.1 follows on with the (indirect) effect of ORDER BY 
> - it has an observable effect only when LIMIT and OFFSET slice the solution 
> sequence.
> 
> """
> Used in combination with LIMIT and OFFSET, ORDER BY can be used to return 
> results generated from a different slice of the solution sequence.
> """
> 
> >
> >9.3 DISTINCT
> >
> >What is the solution of :
> >
> >select distinct ?y where {
> >	?x c:friend ?y
> >}
> >
> >on this graph :
> >
> >ex:Jules c:friend ex:Jimmy
> >ex:Jules c:friend ex:James
> >ex:Jimmy owl:sameAs ex:James
> 
> SPARQL is defined for simple entailment, with no notion of the semantics
> of owl:sameAs. The result of this query is:
> 
>   ?y
> --------
> ex:Jimmy
> ex:James
> 
> The conditions for extending SPARQL to other entailment regimes are given 
> in:
> http://www.w3.org/TR/rdf-sparql-query/#sparqlBGPExtend
> 
> >
> >11.3 Operator Mapping
> >
> >xs:integer, xs:decimal, xs:float, xs:double
> >
> >should be :
> >
> >xsd:integer, xsd:decimal, xsd:float, xsd:double
> 
> Corrected - and checked there are no other "xs:" anywhere in the document
> 
> >
> >operator =
> >
> >[[
> >I think there should be an = operator for plain literals because
> >otherwise, RDFterm-equal applies, in which case :
> >
> >11.4.10 RDFterm-equal
> >
> >RDFterm-equal produces a type error if the arguments are both literal but
> >are not the same RDF term.
> >
> >
> >So, following the current draft :
> >
> >'Jules'@en = 'Jim'@en
> >
> >produces a type error because they are not the same RDF term.
> >
> >It is the same with != < <= > >=
> >]]
> 
> By design, SPARQL does not define semantics for comparing plain literals
> with language tags, as you've noted. Note that query writers can compare
> literals themselves:
> 
>   langMatches(lang(?a), lang(?b)) &&
>   langMatches(lang(?b), lang(?a)) &&
>   (str(?a) = str(?b))
> 
> The Working Group has not been motivated in the past to define the
> comparison operators on plain literals with language tags.
> 
> Section 11.3.1 "Operator Extensibility" licenses SPARQL language extensions 
> that add rows to the operator table, such that implementations may support 
> comparing plain literals with language tags.
> 
> I hope that this addresses this concern; please let us know if not, and
> the Working Group will weigh changes to the operator table versus the
> schedule risks of publishing a new Last Call draft.
> 
> >
> >SPARQL Tests, defined in section 11.4
> >
> >[[regex could operate on xsd:string as well as simple literal.]]
> 
> Similarly, an implementation can add regex working on xsd:strings because 
> it is a type error and can be enhanced.
> 
> >
> >11.4.7 datatype
> >
> >if the the parameter -> if the parameter
> 
> Done
> 
> >11.4.10 RDFterm-equal
> >
> >
> >    * term1 and term2 are equivalent IRIs as defined in 6.4 RDF URI
> >References.
> >    * term1 and term2 are equivalent literals as defined in 6.5.1 Literal
> >Equality.
> >    * term1 and term2 are the same blank node as described in 6.6 Blank
> >Nodes.
> >
> >
> >
> >[[There are no such 6.4, 6.5.1 and 6.6 sections in the current document,
> >so the wording looks strange (in particular when you print the document)]]
> 
> Agreed - I've added: "of [CONCEPTS]" to stress the remote link:
> e.g.
> 
>  * term1 and term2 are equivalent IRIs as defined
>    in 6.4 RDF URI References of [CONCEPTS].
>  * term1 and term2 are equivalent literals as defined
>    in 6.5.1 Literal Equality of [CONCEPTS].
>  * term1 and term2 are the same blank node as described
>    in 6.6 Blank Nodes of [CONCEPTS].
> 
> >
> >
> >[[I think that the 2nd example of RDFterm-equal on dateTime is not
> >appropriate here because in this case, the = operator on dateTime applies
> >and hence not RDFterm-equal()]]
> >
> 
> I defer to Eric on this point.

Yeah, that was from an earlier day. How about this?
Data:
[] foaf:name "Alice" ;
   foaf:schoolpage <http://school.example/> .
[] foaf:name "Bob" ;
   foaf:schoolpage <http://school.example/> .

Query:
SELECT ?name
WHERE { ?b          foaf:name "Bob" .
        ?b          foaf:schoolpage ?schpg .
        ?schoolmate foaf:schoolpage ?schpg
        ?schoolmate foaf:name ?name
        FILTER (?b != ?schoolmate) }

Results:
  ?name
  "Alice"

> >
> >12.1.5 Basic Graph Patterns
> >
> >
> >A Basic Graph Pattern is a set of Triple Patterns.
> >
> >[[SPARQL parsers are required to remove duplicate triples?]]
> 
> They are not required to remove duplicates.
> 1/ {a a} is the same set as {a}, just not canonical.
> 2/ Solving for a bag would yield the same answers.
> 
> >
> >12.2.1 Converting Graph Patterns
> >
> >
> >
> >If the element consists of multiple GroupGraphPatterns then connected with
> >'UNION' terminals, then replace with a sequence of nested union operators:
> >
> >->
> >
> > GroupGraphPatterns connected with 'UNION' terminals [[remove then]]
> 
> Done
> 
> >
> >12.2.2 Examples of Mapped Graph Patterns
> >
> >
> >Example: group consisting of a basic graph pattern, a filter and an
> >optional graph pattern:
> >
> >{ ?s :p1 ?v1} FILTER (?v1 < 3 ) OPTIONAL {?s :p3 ?v3} }
> >Filter( ?v1 < 3 ,
> >  LeftJoin( BGP(?s :p1 ?v1), BGP(?s :p2 ?v2), true) ,
> >  )
> >
> >
> >should be [[replacing 2 by 3]]:
> >
> >
> >{ ?s :p1 ?v1} FILTER (?v1 < 3 ) OPTIONAL {?s :p3 ?v3} }
> >Filter( ?v1 < 3 ,
> >  LeftJoin( BGP(?s :p1 ?v1), BGP(?s :p3 ?v3), true) ,
> >  )
> >
> 
> Fixed by replacing 3 by 2 in the input.
> 
> { ?s :p1 ?v1} FILTER (?v1 < 3 ) OPTIONAL {?s :p2 ?v2} }
> 
> Filter( ?v1 < 3 ,
>   LeftJoin( BGP(?s :p1 ?v1), BGP(?s :p2 ?v2), true) ,
>   )
> 
> >
> >
> >
> >12.2.3 Converting Solution Modifiers
> >
> >
> >M := OrderBy(M, list of of order comparators)
> >
> >->
> >
> >list of  order
> 
> Done
> 
> >
> >12.3.2 Treatment of Blank Nodes
> >
> >
> >Since SPARQL treats blank node IDs in the answer document as scoped to the
> >document ...
> >
> >[[There may be no answer document when the result is accessed through an
> >API, so this reference to answer document looks strange.]]
> 
> We need a name for the whole answer, whether variables bindings or graph. 
> SPARQL defines the query language and the protocol, and the protocol 
> returns documents - APIs are not directly considered in the spec.  The API 
> is accessing the (probably notional) answer document.  APIs are not 
> required to do anything particular but it would seem natural if they 
> behaved the same whether accessing a local query implementation or 
> deserialized results from a remote query service.
> 
> >
> >12.4 SPARQL Algebra
> >
> >
> >Definition: Filter
> >
> >has a effective boolean -> has an effective boolean
> >
> >Definition: Diff
> >
> >{ &#956; | &#956; in &#937;1 such that for all &#956;&#8242; in &#937;2,
> >&#956; and &#956;&#8242; are not compatible }
> >set-union
> >{ &#956; | &#956; in &#937;1 such that for all &#956;&#8242; in &#937;2,
> >&#956; and &#956;' are compatible and expr(merge(&#956;, &#956;')) is
> >false }
> >
> >
> >[[
> >I think the second member of union should be :
> >
> >{ &#956; | &#956; in &#937;1 such that for all &#956;&#8242; in &#937;2,
> >&#956; and &#956;' are compatible => expr(merge(&#956;, &#956;')) is
> >false}
> 
> You suggest replacing "and" by "=>"
> 
> It should be "and" - both parts must be true.  It's not a logical 
> implication inside the conditon.
> 
> >
> >in addition it could be said that: expr(..) is false or returns an error
> 
> Changed to
> expr(...) has an effective boolean value of false which covers the error 
> case.
> 
> >]]
> >
> >Definition: LeftJoin
> >
> >
> >    { merge(&#956;1, &#956;2) | &#956;1 in &#937;1 and &#956;2 in &#937;2,
> >and &#956;1 and &#956;2 are compatible and expr(merge(&#956;1,
> >&#956;2)) is true }
> >set-union
> >    { &#956;1 | &#956;1 in &#937;1 and &#956;2 in &#937;2, and &#956;1 and
> >&#956;2 are not compatible }
> >set-union
> >    { &#956;1 | &#956;1 in &#937;1 and &#956;2 in &#937;2, and &#956;1 and
> >&#956;2 are compatible and expr(merge(&#956;1, &#956;2)) is false }
> >
> >
> >
> >[[
> >I think member 2 and 3 of union should be :
> >
> >    { ... }
> >set-union
> >    { &#956;1 | &#956;1 in &#937;1 such that for all &#956;2 in &#937;2, 
> >&#956;1 and &#956;2 are not compatible }
> >set-union
> >    { &#956;1 | &#956;1 in &#937;1 such that for all &#956;2 in &#937;2, 
> >&#956;1 and &#956;2 are compatible => expr(merge(&#956;1, &#956;2)) is
> >false or returns an error}
> >
> >]]
> >
> 
> As above.
> 
> 
> >12.5 Evaluation Semantics
> >
> >
> >
> >Definition: Evaluation of Join(P1, P2, F)
> >
> >eval(D(G), Join(P1, P2)) = Join(eval(D(G), P1), eval(D(G), P2))
> >eval(D(G), Join(P1, P2), F) = Filter(F, Join( eval(D(G), P1), eval(D(G),
> >P2) ) )
> >
> >
> >[[
> >I think there should be one rule for Join(P1, P2) without F, and one rule
> >for Filter(F, P)
> >]]
> 
> corrected as suggested - that was a previous style of having joins to be 
> like LeftJoin.
> 
> 
> >
> >
> >
> >
> >
> >Definition: Evaluation of LeftJoin(P1, P2)
> >
> >should be:
> >
> >Definition: Evaluation of LeftJoin(P1, P2, F)
> 
> Corrected
> 
> >
> >Definition: Evaluation of a Graph Patten
> >
> >
> >eval(D(G), Graph(IRI,P)) = eval(D(D[i]), P)
> >
> >should be [[replacing i by IRI]]:
> >
> >eval(D(G), Graph(IRI,P)) = eval(D(D[IRI]), P)
> >
> 
> Corrected
> 
> >
> >
> >
> >12.6 Extending SPARQL Basic Graph Matching
> >
> >
> >mappijng  ->  mapping
> 
> Corrected

If you are content with this response, please reply, prefixing your
Subject: with [DONE]. (This is for our issue tracking system.) Of
course, if you are not satisfied, reply so we can resolve the
remaining issues.
-- 
-eric

office: +1.617.258.5741 NE43-344, MIT, Cambridge, MA 02144 USA
mobile: +1.617.599.3509

(eric@w3.org)
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Received on Monday, 23 April 2007 23:58:16 GMT

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