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DTB: Problem/Erratum for DTBin function string-join

From: Axel Polleres <axel.polleres@deri.org>
Date: Mon, 17 Aug 2009 21:28:27 +0100
Message-ID: <4A89BD6B.80206@deri.org>
To: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>
Hi all,

While working on the all-builtins use case, I realize a slight 
error/problem in DTB now with the function:

func:string-join(...)

its xpath/xquery counterpart fn:string-join(...)

takes two arguments:
- a sequence of strings
- a "separator" string

now I realize - since this function was introduced when we didn't heva 
lists in RIF yet, that we seem to have expected a "flattened" list as 
input, i.e. we give the schemas

( ?arg1 ?arg2; func:string-join(?arg1 ?arg2 ) )

( ?arg1 ?arg2 ?arg3; func:string-join(?arg1 ?arg2 ?arg3 ) )

...

( ?arg1  ?arg2 ... ?argn; func:string-join(?arg1 ?arg2 ... ?argn ) )


Anyways, the semantics is defined in terms of fn:string-join, which 
didn't work so far, but only works with a small fix, i.e. interpreting 
the first n-1 arguments as the sequence argument of the CPAth/Xquery 
fn:string-join function. "Historically" this is IMO what we meant, as 
there was no lists.

Thus, I see two options for fixing this:

a) stick with the flattened version, interpreting the first n-1 
arguments as the sequence argument of the CPAth/Xquery fn:string-join 
function and the last argument as the separator string.

b) make the function with a fixed arity of 2,  the domain of the first 
argument being a list of strings and the second argument the separator 
string.

I implemented option a) now, since it is the "least intrusive" change to 
the current doc, see

http://www.w3.org/2005/rules/wiki/index.php?title=DTB&diff=10665&oldid=10495

however, b) seems somehow the more natural way to proceed. The 
disadvantage/worry I see with b) is that we might want to implement
"emulating" sequences by lists as input in other functions as well... 
Opinions?

Axel



-- 
Dr. Axel Polleres
Digital Enterprise Research Institute, National University of Ireland, 
Galway
email: axel.polleres@deri.org  url: http://www.polleres.net/
Received on Monday, 17 August 2009 20:29:14 GMT

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