fn:concat and afn:strJoin not appending returning empty results.

[Deepak Konidena <de...@cornell.edu>]

Hi,

When I try to use fn:concat and afn:strJoin in the following fashion:

PREFIX fn: <http://www.w3.org/2005/xpath-functions#>
PREFIX afn: <http://jena.hpl.hp.com/ARQ/function#>

select ?ALLTEXT ?d ?e ?h ?j ?k ?l where{

  ?a rdf:type foaf:Person ; ?b ?c .
  ?c rdf:type core:Position .

   optional { ?c core:hrJobTitle ?d . } .
   optional { ?c core:involvedOrganizationName ?e . } .
   optional   { ?c core:positionForPerson ?f . ?f rdfs:label ?h .}
   optional { ?c core:positionInOrganization ?i . ?i rdfs:label ?j .}
   optional { ?c core:titleOrRole ?k .}
   optional { ?c rdfs:label ?l . }

LET (?ALLTEXT := fn:concat(?k, " ", ?l )) .
LET (?ALLTEXT := afn:strJoin(?k, " ", ?l ))
}


The variable ALLTEXT gets populated only when both ?k and ?l are not empty. When one
Of them is empty, ALLTEXT is showing an empty result.

How would I modify this behavior? Ideally, you would expect fn:concat to concatenate even empty results.

Am I doing anything wrong here?

Thanks,
Deepak Konidena.

Re: fn:concat and afn:strJoin not appending returning empty results.

[Andy Seaborne <an...@epimorphics.com>]

On 02/05/11 21:28, Deepak Konidena wrote:
> Hi,
>
> When I try to use fn:concat and afn:strJoin in the following fashion:
>
> PREFIX fn:<http://www.w3.org/2005/xpath-functions#>
> PREFIX afn:<http://jena.hpl.hp.com/ARQ/function#>
>
> select ?ALLTEXT ?d ?e ?h ?j ?k ?l where{
>
>    ?a rdf:type foaf:Person ; ?b ?c .
>    ?c rdf:type core:Position .
>
>     optional { ?c core:hrJobTitle ?d . } .
>     optional { ?c core:involvedOrganizationName ?e . } .
>     optional   { ?c core:positionForPerson ?f . ?f rdfs:label ?h .}
>     optional { ?c core:positionInOrganization ?i . ?i rdfs:label ?j .}
>     optional { ?c core:titleOrRole ?k .}
>     optional { ?c rdfs:label ?l . }
>
> LET (?ALLTEXT := fn:concat(?k, " ", ?l )) .
> LET (?ALLTEXT := afn:strJoin(?k, " ", ?l ))
> }
>
>
> The variable ALLTEXT gets populated only when both ?k and ?l are not empty. When one
> Of them is empty, ALLTEXT is showing an empty result.

By not empty, I take it you mean unbound.

> How would I modify this behavior? Ideally, you would expect fn:concat to concatenate even empty results.
>
> Am I doing anything wrong here?

The behaviour is correct and nothing to do with fn:concat.

For any strict function:

function(unbound) -> error

because the arguments are evaluated before the function is called, and 
eval(?x) -> error for unbound ?x

An error in LET will leave it unbound.

Try:
SELECT * { LET ( ?A := 1/0 ) }

You may wish to use COALESCE:

BIND (COALESCE(?k, "") as ?k2)

to give a default value to ?k as ?k2.  Only new variables are legal in 
BIND but it is SPARQL 1.1.

>
> Thanks,
> Deepak Konidena.
>

	Andy

Re: fn:concat and afn:strJoin not appending returning empty results.

[Damian Steer <d....@bristol.ac.uk>]

On 2 May 2011, at 21:28, Deepak Konidena wrote:

> Hi,

Hi Deepak,

> LET (?ALLTEXT := fn:concat(?k, " ", ?l )) .
> LET (?ALLTEXT := afn:strJoin(?k, " ", ?l ))
> }
> 
> 
> The variable ALLTEXT gets populated only when both ?k and ?l are not empty. When one
> Of them is empty, ALLTEXT is showing an empty result.

COALESCE [1] seems like you best bet:

LET (?ALLTEXT := COALESCE(fn:concat(?k, " ", ?l ), ?k, ?l, ""))

but no doubt there are cunning alternatives I'm missing.

Damian

[1] <http://www.w3.org/TR/sparql11-query/#func-coalesce>