Re: Blank nodes scope in CONSTRUCT queries

Doing this with bNodes is difficult, but the URI() (a.k.a. IRI) function in SPARQL 1.1 can be used to do roughly what you want.

http://www.w3.org/TR/sparql11-query/#func-iri

For example:

   BIND(URI(CONCAT("http://my.example/".MD5(?x)) AS ?subj)

will bind a new variable ?subj to a URI which is derived from the value of ?x.

There is also a BNODE() function for creating bNodes, but it has the same scope rules as CONSTRUCT.

- Steve

On 11 Oct 2011, at 12:03, Miguel wrote:

> Hello,
> I have been thinking on a possible extension of SPARQL CONSTRUCT queries.
> Both in SPARQL Recommendation and in the 1.1 Working Draft the scope
> of blank nodes in CONSTRUCT queries is defined as follows:
> 
> "A template can create an RDF graph containing blank nodes. The blank
> node labels are scoped to the template for each solution. If the same
> label occurs twice in a template, then there will be one blank node
> created for each query solution, but there will be different blank
> nodes for triples generated by different query solutions."
> 
> I modified the example in the specification to show why I propose to
> increase the flexibility of the CONSTRUCT form
> 
> CONSTRUCT { ?x vcard:N _:v .
>            _:v vcard:givenName ?gname .
>            _:v vcard:familyName ?fname .
>            _:v vcard:email ?email }
> WHERE
> {
>    { ?x foaf:firstname ?gname } UNION  { ?x foaf:givenname   ?gname } .
>    { ?x foaf:surname   ?fname } UNION  { ?x foaf:family_name ?fname } .
>    ?x foaf:mbox ?email .
> }
> 
> But if some person has more than one email address the query gives
> duplicated vcards for them.
> 
> This is a general problem, there is often need to group results in
> similar ways. In SQL or SPARQL SELECT this can be done using an ORDER
> BY to group together related tuples and "breaking" in the host system
> by a key value change.
> 
> A similar and more general result could be reached in CONSTRUCT
> queries if we allow to explicitly declare the scope of each blank node
> in the template.
> 
> As a syntax example I add a (optional) SCOPE clause to the CONSTRUCT queries:
> 
> CONSTRUCT
>  {
>    ?x vcard:N _:v .
>    _:v vcard:givenName ?gname .
>    _:v vcard:familyName ?fname .
>    _:v vcard:email ?email
>  }
> SCOPE
>  {
>    _:v (?x)
>  }
> WHERE
> {
>    { ?x foaf:firstname ?gname } UNION  { ?x foaf:givenname   ?gname } .
>    { ?x foaf:surname   ?fname } UNION  { ?x foaf:family_name ?fname } .
>    ?x foaf:mbox ?email .
> }
> 
> meaning that for _:v a different blank node is created for each
> different ?x binding (and not for each ?x-?gname-?fname-?email
> binding).
> This is a simple example there is a single blank node linked to a
> single variable, but we could have several blank nodes, each one
> linked to a different subset of variables.
> For a blank node not in SCOPE, the default scoping is as in the
> existing definition (it depends from all the variables)
> 
> Please let me know what you think of this proposal and excuse for my
> poor English.
> 
> Thanks,
> Miguel
> 
>

Received on Tuesday, 11 October 2011 19:05:22 UTC