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Re: function library summary and issues

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Sun, 28 Nov 2010 17:56:43 +0000
Message-ID: <4CF297DB.8040609@epimorphics.com>
To: Steve Harris <steve.harris@garlik.com>
CC: Gregory Williams <greg@evilfunhouse.com>, SPARQL Working Group <public-rdf-dawg@w3.org>


On 28/11/10 16:30, Steve Harris wrote:
> On 2010-11-28, at 15:34, Andy Seaborne wrote:
>>
>> On 28/11/10 15:14, Steve Harris wrote:
>>>>>   If we require it, it seems natural to me to have:
>>>>>
>>>>>     CONCAT("a"@en, "b"@en) ->   "ab"@en
>>>>>     CONCAT("a"@en, "b"@fr) ->   "ab"  (or error)
>>>>>     CONCAT("a"@en, "b") ->   "ab"  (or error)
>>> There are legitimate cases where you might have some literals without tags, and some with, and want to concatenate them, without having loads of logic.
>>
>> (just sorting out the small details)
>>
>> This can be achieved by using STR:
>>
>> CONCAT(STR("a"@en), STR("b"@fr)) ->   "ab"
>>
>> Is that too much logic?
>
> That's not what I was thinking of as logic, but then you can't preserve the lang tag, if one applies. Might not matter though.
>
> I was thinking of cases like:
>
> <distilation>  a :Process ;
>                :name "Distillation", "Дестилация"@ru ;
>                :produces "C2H5OH" .
>
> SELECT (CONCAT(?name, " ->  ", ?produces))
> WHERE {
>    ?process a :Process ;
>             :name ?name ;
>             :produces ?produces .
>     FILTER(lang(?name) = "ru" || lang(?name) = "")
>     FILTER(lang(?produces) = "ru" || lang(?produces) = "")
> }
>
> If we preserve lang tags then you'll get:
>
> "Дестилация ->  C2H5OH"@ru
> "Distillation ->  C2H5OH"
>
> With STR() you'd lose the lang tag.

I came up with:

STRDT(CONCAT(?name, " ->  ", ?produces), lang(?name))

in other words, produce a string without lang tag and separate out the 
decision of which language to use rather than have a fixed policy in 
CONCAT.  You can even have a mixture of language tags (@en and @en-uk 
and @en-UK) abd decide somehow..

Seeing that example, I think I prefer this approach - do the least in 
CONCAT and leave the rest to the query logic.

> This might be nonsense scientifically speaking, the example I'm most familiar with is from signal processing, but it's hard to explain without a lot of context. I hope it makes the point though.

To summarise: We have the following possibilities:

0/ Do/Don't specific the use of CONCAT in the case of lang tags.

Different lang tags (two or more distinct lang tags in a the CONCAT arg 
list):

1/ -> error
2/ -> simple literal

Mixture of simple literals and one distinct lang tag
3/ -> error
4/ -> simple literal
5/ -> literal with that lang tag

	Andy
Received on Sunday, 28 November 2010 17:57:24 GMT

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