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Re: comments on SPARQL 1.1 Query Last Call WD: builtin functions

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Tue, 01 Nov 2011 15:07:19 +0000
Message-ID: <4EB00B27.1070602@epimorphics.com>
To: public-rdf-dawg-comments@w3.org
CC: jeen Broekstra <jeen.broekstra@gmail.com>


On 02/08/11 01:24, Jeen Broekstra wrote:
>
> Hello WG,

Hi Jeen,

>
> I have a couple of comments on the current Last Call working draft for
> SPARQL 1.1 query, mainly about the set of built-in functions (section
> 17.4). These comments came about as part of me implementing these
> functions in Sesame's SPARQL processor.

We're glad to hear that there is now an implementation of SPARQL 1.1 
query and update for Sesame. We hope you will participate in the 
implementation report that the working group will be doing as part of 
the W3C process.

>
> 1. String functions
>
> The current set of built-in functions on strings seems rather
> arbitrarily chosen, with little evident use case requirements backing
> them up.
>
> For example, while both fn:string-length and fn:substring are included,
> fn:substring-before and fn:substring-after are not, nor is there any
> form of 'indexOf'-function. This makes it currently not possible in
> SPARQL to determine the substring of a string based on a character match.
>
> My comment is not that these functions should or should not be included
> per se, but rather a question: what criteria did the WG use to decide
> which functions 'make the cut'?

Having reviewed the choice of string functions, and having sought to 
understand the choices in XQuery/Xpath functions and operators, the 
working group has decided to add functions STRBEFORE (c.f. 
fn:substring-before), STRAFTER (c.f. fn:substring-after) and REPLACE 
(c.f. fn:replace). These function take into account the RDF data model - 
for example the handling of literal with language tags.

>
> 2. Hash functions
>
> Perhaps my strongest problem with the current Working Draft is the
> inclusion of 6 variations for calculating a hash. Arguably calculating a
> hash is a _very_ outlying use case that comes up rarely in practical
> applications of SPARQL. I'm not denying there are valid use cases for
> it, but adding six different varieties seems, frankly, outlandish.
>
> There is a practical consideration for me in this as well: on the Java
> platform, SHA-224 in particular is not supported by the default
> cryptography architecture. The fact that SPARQL includes it forces me to
> add a third-party dependency to my SPARQL implementation for a feature
> that very few users will ever need. I find this wasteful and an
> unncessary burden, both on implementors and on users of the software.
>
> Given that the SPARQL specification supports the adding of custom
> functions, so that any vendor who needs to can extend the language, I
> would suggest that this kind of niche functionality has no place in the
> core spec and should be removed, or at the very least only a minimal set
> of hash functions (2 or 3, tops) should be required. In picking this
> subset, the WG should IMHO consider which algorithms are most commonly
> used and supported on various platforms.

The working group reviewed the choice of hash functions and also the 
availability of implementations for various programming languages. As a 
decision criteria, the working group choose to keep the SHA2 functions 
mentioned in "XML Signature Syntax and Processing Version 1.1" [1] which 
is SHA-256, SHA-384, SHA-512. MD5, while not secure, is known to be used 
as a checksum and SHA1 is used by FOAF.

Therefore, the working group has removed SHA-224, which is the function 
causing you some implementation difficulties.

>
> Regards,
>
> Jeen Broekstra

Changes for both string functions and hash functions are drafted in the 
editors' working draft [2]. There will be a second last call for the 
SPARQL 1.1 Query document because these changes materially affect 
implementations.

We would be grateful if you would acknowledge that your comment has been 
answered by sending a reply to this mailing list.

Andy (on behalf of the SPARQL WG)

[1] http://www.w3.org/TR/xmldsig-core1/
[2] http://www.w3.org/2009/sparql/docs/query-1.1/rq25.xml
Received on Tuesday, 1 November 2011 15:07:56 GMT

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