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Re: Editorial thread for BGP matching

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Wed, 25 Jan 2006 15:06:28 +0000
Message-ID: <43D793F4.9000402@hp.com>
To: "Patrick J. Hayes" <phayes@ihmc.us>
CC: RDF Data Access Working Group <public-rdf-dawg@w3.org>



Patrick J. Hayes wrote:
> Reading through, some miscellaneous 
> comments/questions/suggestions(?).
> ------
> 2.1.4
> "Triple Patterns are grouped together with {}(braces)."
> Possibly mention here that these groupings determine scope 
> of bnode identifiers(?) <<Do they, in fact? That is, 
> should we read
> {{_:a :p :q .}
> {_:a :r :b .}}
> as having two bnodes in it, or one? Im presuming two, as 
> otherwise what are the {} boundaries for? >>

It's two BGPs.

{} really delimit groups.  I'm going to add that a (filtered)BGP is a sequence 
of triple patterns or filters.

Which answers the question of what

{ BGP1 optional { BGP2 } BPG3 }

really means.

> 
> 2.1.5 Examples of Query Syntax
> 
> The reader is tempted to ask, what about mixing the 
> variable prefixes in a single query, such as
> 
> PREFIX  dc: <http://purl.org/dc/elements/1.1/> PREFIX  : 
> <http://example.org/book/> SELECT  $title WHERE   { :book1 
>  dc:title  ?title }
> 
> Is that legal? If so, suggest fix one of the examples to 
> show this.

Good idea - done.

> 
> BTW, some of the example answer tables have the variable 
> name with ? included, others not: suggest they should be 
> consistent for clarity.

I found one. If you find any more, please let me know.

I believe there is a daemon that goes round putting them back in when I'm not 
looking.

> 
> 2.1.7
> The bindings shown are to quoted strings which aren't 
> typical. Might be better to show a binding to a URI(?)
> 

I've changed the y binding to <http://example/a>

> 2.2
> 
> "This definition of RDF Term collects together several 
> basic notions from the RDF data model."
> //
> "......the RDF data model, but updated to refer to IRIs 
> rather than URIs."

Done. but s/URIs/RDF URI references/

Good link.

> (Could refer to 
> http://www.w3.org/TR/rdf-concepts/#section-Graph-URIref 
> "Note: this section anticipates an RFC on 
> Internationalized Resource Identifiers. Implementations 
> may issue warnings concerning the use of RDF URI 
> References that do not conform with [IRI draft] or its 
> successors.".)
> 
> "Note that all IRIs are absolute; they may or may not 
> include a fragment identifier [RFC3987, section 3.1]. Also 
> note that IRIs include URIs [RFC3986] and URLs."
> ? Should perhaps say here that they include URI references 
> (?)

I believe that 3986 cleared up use of URI reference to be the case of not 
absolute and that #frags are part of absolute URIs.

> 
> Definition:
> "A query variable is a member of the set V where V is 
> infinite and disjoint from RDF-T."
> Why infinite? We only need enough for a single query.

It was a comment.  I think that the defn being here does not carry teh 
connection to just one query.

> 
>   "The following triple pattern has a subject variable 
> (the variable book), a predicate of dc:title and an object 
> variable (the variable title)."
> predicate of//predicate

Done

> 
> Triple pattern: Why not allow bnodes in property position 
> as well, with the same disclaimers about not matching any 
> current RDF graph? There isn't any good semantic reason to 
> forbid that case either. (If this would require a WG 
> decision, forget it :-)

The syntax allows it.  Defn fixed.

Definition: Triple Pattern
A triple pattern is member of the set:
     (RDF-T union V) x (I union RDF-B union V) x (RDF-T union V)


(Could even add literals for complete symmetry. Not done as literals in the 
predicate would be rather confusing for no value.)

> 
> ---------
> 
> I started commenting on section 2.4 and 2.5 but its easier 
> to redraft them. (The current definition of 'pattern 
> solution" is wrong and can't be fixed until the scoping 
> graph is mentioned, which requires re-ordering some 
> material).
> For my best attempt so far, see 
> http://www.ihmc.us/users/phayes/Section2.4revized.html  (I 
> cut out some of your html and edited it. <<comments like 
> this>> )
> 
> Im rather confused, I confess, by the various distinctions 
> (pattern solution, query solution,...) in section 2.4, so 
> that section is still a muddle. I think some of it ls left 
> over from earlier versions. For example, Pattern Solution 
> refers to "RDF terms occurring in G" which is wrong. In 
> fact, I don't think there is any way to distinguish 
> between variable substitution and pattern solution at this 
> point, since the latter can't be defined properly until 
> the scoping set has been mentioned.
> 
> -------
> 
> Sorry, I only got back to this tonight, so it likely needs 
> more work but I'll send this now to get it to you before 
> the telecon.
> 
> Pat
> 
> 

More to follow.

	Andy
Received on Wednesday, 25 January 2006 15:06:44 GMT

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