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Re: review of rq23 1.377

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Mon, 13 Jun 2005 12:53:44 +0100
Message-ID: <42AD73C8.4040002@hp.com>
To: kendall@monkeyfist.com, DAWG Mailing List <public-rdf-dawg@w3.org>

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(This is the last reply to the comments message)

Comments accepted unless noted below:

See CVS log for things accepted that aren't purely editorial.
Latest is v1.389

	Andy


Kendall Clark wrote:
> Andy & Eric,
> 
> I'm attaching my review of 1.377 of rq23. It's an annotated copy of the spec
> itself. That seemed a bit easier for me and, hopefully, for you guys to
> process. I'm hoping that the W3 list archiver turns HTML attachments into
> links.
> 
> Anyway, I'm happy to discuss any of the comments in the review. FYI, I
> stopped the review around section 11.1. I made nearly 300 <strike> or <ins>
> annotations, and then I got really tired of doing that. :>
> 
> All in all, good show on the spec!
> 
> Kendall Clark
> 
> 
> ------------------------------------------------------------------------
> 
> W3C <http://www.w3.org/>
> 
> 
>   SPARQL Query Language for RDF

...

>     7 RDF Dataset
> 
> The RDF data model expresses information as graphs, comprising of 
> triples with subject, predicate and object. Many RDF data stores hold 
> multiple RDF graphs,graphs and record information about each graph, 
> allowing an application to make queries that involve information from 
> more than one graph.

Left as is.

> 
> A SPARQL query is madeexecuted against an /RDF Dataset/ which may 
> represents such a collection of graphs [Is one graph "such a collection 
> of graphs"?].

Yes.  (As is zero)

> Different parts of the query are may be matched against 
> different graphs as described in the next section <#queryDataset>. There 
> is one graph, the default graph, which does not have a name, and zero or 
> more named graphs, each identified by IRI.
> 
> *Definition:* RDF Dataset
> 
> An RDF dataset is a set
>      { G, (<u_1 >, G_1 ), (<u_2 >, G_2 ), . . . (<u_n >, G_n ) }
> where G and each G_i are graphs, and each <u_i > is a IRI. Each <u_i > 
> is distinct.
> 
> G is called the default graph. (<u_1 >, G_i ) are called named graphs.
> 
> In the previous sections, all queries have been shown executed against a 
> single, default graph. A query does not need to involvebe executed 
> against the default graph; the query can just involvemay be executed 
> against the named graphs. [Has this been synched up with the design of 
> fromUnionQuery we decided on Tuesday? I'm not sure it's consistent with 
> that design.]

Could you provide an example where it's not consistent?

> 
> @@Need not have a default graph.
> 
> 
>       7.1 Examples of RDF Datasets
. . .
> 
> In this example, the default graph contains the publisher names of two 
> named graphs [I don't know what is meant by "the publisher names of two 
> named graphs"...]. 

"the names of the publishers of two named graphs"
(the graph has predciate dc:publisher)

> The triples in the named graphs are not visible in 
> the default graphand, thought of as the default knowledge base, the 
> application is not directly trusting the information in the named graphs.
> 
> 
. . .
> 
> [I see very little value in this section. I won't request, at this 
> stage, that it be struck entirely, but I think it's a good idea. At the 
> very least, there are three or four problematic sentences or phrases 
> that need to be reworked or struck.]
> 
> 
>     8 Querying the Dataset
> 
. . .
> 
>     9 Specifying RDF Datasets
> 
> A SPARQL query may specify the dataset against which it is to be 
> executed for the query.

"A SPARQL query may specify the dataset to be used for matching."

. . .
> 
> @@Add text to say that specifying the dataset overrides an service dataset.
> 
> @@ Text from DanC:

Text added (with edits)

> 
> The FROM and FROM NAMED keywords allow a query to specify an RDF dataset 
> by reference; they indicate that the dataset should include graphs that 
> are obtained from representations of the resources identified by the 
> given IRIs (i.e. the absolute form of the given IRI references). The 
> dataset resulting from a number of FROM and FROM NAMED clauses is
> - a default graph consisting of the merge of the graphs referred to in 
> the FROM clauses
> - a set of (IRI, graph) pairs, one from each FROM NAMED clause.
> 
> 
>       9.1 Specifying the Default Graph
> 
. . .

> @@Text from DanC:
> 
>  NOTE: The "FROM NAMED" syntax suggests that the IRI identifies the 
> corresponding graph, but actually the relationship between a URI and a 
> graph in an RDF dataset is indirect: the IRI identifies a resource, and 
> the resource is represented by a graph (or, more precisely: by a 
> document that serializes a graph). See also the diagram in section "1. 
> Introduction" of [webarch].
> 
> http://www.w3.org/TR/webarch/#intro

Text added (with edits)

. . .
> 
>     10 Query Result Forms
> 
> SPARQL has a number offour query formsresult forms for returning 
> results. These resultquery

left second.

 > forms use the solutions from pattern matching
> to form result sets or RDF graphs. The query forms are:
> 
>     SELECT <#select>
>         Returns all, or a subset of, the variables bound in a query
>         pattern match.
>     CONSTRUCT <#construct>
>         Returns an RDF graph constructed by substituting variables in a
>         set of triple templates. 
>     DESCRIBE <#describe>
>         Returns an RDF graph that describes the resources found.
>     ASK <#ask>
>         Returns a boolean indicating whether a query pattern matches or not.
> 
> The SPARQL Variable Binding Results XML Format 
> <http://www.w3.org/TR/rdf-sparql-XMLres/> can be used to serialize 
> result sets from a |SELECT| query or the boolean result of an |ASK| query.
> 
> 
>       10.1 Solution Sequences and Result Forms
> 
> Query patterns generate a set of solutions, each solution being a 
> function from variables to RDF terms. These solutions are treated as a 
> sequence. A number of sequence modifiers are [I think "may be" might be 
> better than "are" here?] applied before the solutions are used to form 
> the final query result.

"Any sequence modifiers are applied ..."

They are not optional.

> 
> *Definition:* Solution Sequence
> 
. . .
> 
> 
>         OFFSET
> 
> |OFFSET| causes the solutions generated to start after the specified 
> number of solutions. An |OFFSET| of zero has no effect.
> 
> The order in which solutions are returned is initially undefined; thus 
> so using |LIMIT| and |OFFSET| to select different subsets of the query 
> solutions will given not be useful unless the order is made predictable 
> by ensuring ordered results using | ORDER BY|.

Left as is.

> 
> PREFIX foaf:    <http://xmlns.com/foaf/0.1/>
> 
> SELECT  ?name
> WHERE   { ?x foaf:name ?name }
> ORDER BY ?name
> LIMIT   5
> OFFSET  10
> 
> *Definition:* Offset Solution Sequence
> 
> An Offset Solution Sequence with respect to another solution sequence S, 
> is one which starts at a given index of S.
> 
> For solution sequence S = (S_1 , S_2 , . . . , S_n ), the offset 
> solution sequence
> offset(S, k), k >= 0  is
>      (Sk, Sk+1, . . ., S_n ) if n >= k
>      (), the empty sequence, if k > n
> 
> 
>       10.2 Selecting Variables
> 
> The SELECT form of results returns the variables directly. The syntax 
> |SELECT *| is shorthand for an abbreviation "select all the named 
> variables"that selects all of the named variables.
> 
> @prefix  foaf:  <http://xmlns.com/foaf/0.1/> .
> 
> _:a    foaf:name   "Alice" .
> _:a    foaf:knows  _:b .
> _:a    foaf:knows  _:c .
> 
> _:b    foaf:name   "Bob" .
> 
> _:c    foaf:name   "Clare" .
> _:c    foaf:nick   "CT" .
> 
> 
> PREFIX foaf:    <http://xmlns.com/foaf/0.1/>
> SELECT ?nameX ?nameY ?nickY
> WHERE
>   { ?x foaf:knows ?y ;
>        foaf:name ?nameX .
>     ?y foaf:name ?nameY .
>     OPTIONAL { ?y foaf:nick ?nickY } 
>   }
> 
> nameX 	nameY 	nickY
> "Alice" 	"Bob" 	 
> "Alice" 	"Clare" 	"CT"
> 
> Results can be thought of as a table or result set, with one row per 
> query solution. Some cells may be empty because a variable is not bound 
> in that particular solution.
> 
> Result sets can be accessed by the local API but also can be serialized 
> into either XML or an RDF graph[I request this be removed, as there is 
> no other mention of this anywhere in our specs, nor is there any 
> specification of what this RDF graph might look like.].

Done (the testing does describe the vocabulary).

  The Query
> Results XML Format <http://www.w3.org/TR/rdf-sparql-XMLres/> [Use the 
> full form of the title here]form of this result set gives:
. . .
> 
>       10.3 Constructing an Output Graph
> 
. . .
> 
> The use of variable ?x in the template, which in this example will be 
> bound to blank nodes (which have labels |_:a| and |_:b| in the data) and 
> cause different blank node labels (|_:v1| and |_:v2|) as shown by the 
> results.[As written, this is a sentence fragment or incomplete sentence. 
> It's missing a main verb. Not sure about replacement text because I'm 
> not sure what was intended.]
> 
> 
>         Accessing Graphs in the RDF Dataset
> 
...
> 
> where |app:myDate| identifiedindentifies an extension function 
???indentifies?
> <#extensionFunctions> to turn the data format into an |xsd:dateTime| RDF 
> Term.
> 
. . .
> 
> 
>       10.4 Descriptions of Resources
> 
> The |DESCRIBE| form returns a single result RDF graph containing RDF 
> data about resources. This data is not prescribed by a SPARQL query, 
> where the query client would need to know the structure of the RDF in 
> the data source, but, instead, is determined by the SPARQL query processor.
> 
> The query pattern is used to create a result set. The | DESCRIBE| form 
> takes each of the resources identified in a solution, together with any 
> resources directly named by IRI, and assembles a single RDF graph by 
> taking a "description" from the target knowledge base. The description 
> is determined by the query processor implementation and should provide a 
> useful description of the resource, where the meaning of"useful" is left 
> to nature of the information in the data sourcedetermined by the query 
> processor, the knowledge base, or other domain-specific information.

"""
where the meaning of "useful" is determined by the information publisher.
"""

> 
> If a data source,source has no information about a resource, no RDF 
> triples are added to the result graph but the query does not fail.
> 
. . .

> 
>       10.5 Asking "yes or no" boolean questions

Left.  "Boolean valued" questions seems more correct but unhelpful.

> 
> Applications can use the |ASK| form to test whether or not a query 
> pattern has a solution. No information is returned about the possible 
> query solutions, just whether the server can find one or not.
> 
> @prefix foaf:       <http://xmlns.com/foaf/0.1/> .
> @prefix rdf:        <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
> @prefix rdfs:       <http://www.w3.org/2000/01/rdf-schema#> .
> 
> _:a  foaf:name       "Alice" .
> _:a  foaf:homepage   <http://work.example.org/alice/> .
> 
> _:b  foaf:name       "Bob" .
> _:b  foaf:mbox       <mailto:bob@work.example> .
> 
> PREFIX foaf:    <http://xmlns.com/foaf/0.1/>
> ASK  { ?x foaf:name  "Alice" }
> 
> yes
> 
> The Query Results XML Format <http://www.w3.org/TR/rdf-sparql-XMLres/> 
> [Full form of title...]form of this result set gives:
> 
> <?xml version="1.0"?>
> <sparql xmlns="http://www.w3.org/2001/sw/DataAccess/rf1/result2">
>   <head></head>
>   <results>
>     <boolean>true</boolean>
>   </results>
> </sparql>
> 
> On the same data, the following returns no match because Alice's |mbox| 
> is not mentioned.
> 
> PREFIX foaf:    <http://xmlns.com/foaf/0.1/>
> ASK  { ?x foaf:name  "Alice" ;
>           foaf:mbox  <mailto:alice@work.example> }
> 
> no
> 
> *Definition:* ASK
> 
> Let Q = (GP, DS, SM, ASK) where
> 
>     * GP is a graph pattern <#defn_GraphPattern>
>     * DS is an RDF Dataset <#defn_RDFDataset>
>     * SM is a set of solution modifiers <#defn_SolutionSequenceModifier>
> 
> and QS is the set of solution formed by matching dataset DS with graph 
> pattern GP then the ASK result is true if SM(QS) is not empty, otherwise 
> it is false.
Received on Monday, 13 June 2005 11:57:33 GMT

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