Re: sqrt [was: Wishlist for SPARQL 1.2: Compatible query-hints, extra math operators]

On Wed, Jul 31, 2013 at 5:06 AM, Andy Seaborne <andy@apache.org> wrote:

> On 30/07/13 15:05, Jerven Bolleman wrote:
> ...
>
>> The second is an expansion of the basic math operators to include at
>> least (square)root. (square)root is very hard to implement using the
>> current SPARQL constructs yet is a very useful function. (even if not
>> exact)
>>
>
> The SPARQL 1.1 library was decided mainly by taking the non-sequence
> related functions from XQuery/XPath Functions and Operators (F&O), sorting
> out a few details of RDF/SPARQL evaluation, and adding some SPARQL specific
> functions (e.g. STRDT).
>
> F&O is an excellent resource because it defines exactly what all the
> operations do.  It is (oddly?) lacking on numeric operations like sqrt and
> similar but there may be a good reason for that.
>
> I agree it would be good to have sqrt.  Let's hope that implementations
> add it as an URI-callable function.
>
> If we implementers decide on the URI, then queries will be portable.
>
> http://www.w3.org/ns/sparql is supposed to be populated with URIs for
> every function with a keyword in SPARQL.  That action (389) got lost.
>
> So ...
>
> prefix http://www.w3.org/ns/sparql#
>
> sfn:sqrt(numeric) -> double.
>
> What else (within reason!)?


When it comes to function extensions for common operations like math, I
usually adopted the XPath functions myself. For sqrt, this appears in the
math: namespace.

math:  http://www.w3.org/2005/xpath-functions/math

The list for XQuery/XPath Operators 3.0 includes:

math:pi, math:exp, math:exp10, math:log, math:log10, math:pow, math:sqrt,
math:sin, math:cos, math:tan, math:asin, math:acos, math:atan, math:atan2

These are functions that are already defined by a W3C standard, and these
standards should be compatible wherever possible. Why not use these?

Paul