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Re: function library summary and issues

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Wed, 24 Nov 2010 15:20:27 +0000
Message-ID: <4CED2D3B.9080401@epimorphics.com>
To: Axel Polleres <axel.polleres@deri.org>
CC: SPARQL Working Group <public-rdf-dawg@w3.org>
We are making slow progress on this.  This message is to put a more 
concrete proposal on the table for further WG modification, it's based 
on what I have heard/seen so far but I may well have missed something.

Decision point 1:
Is the list below agreed?
http://lists.w3.org/Archives/Public/public-rdf-dawg/2010OctDec/0188.html

Decision point 2:
Whether to add keywords or whether to have only URIs.
Possible keywords below.

Decision point 3:
What URIs?
I'm assuming there will be URIs for all functions in SPARQL. We need 
sparqlfn: for the ones we have from SPARQL 1.0 and adding for SPARQL 1.1 
anyway (e.g. IRI())

Decision point 3:
What to do about xsd:string vs simple literal?

Practicality suggests simple literals are important.
We can overlay on XSD F&O so for example:

   CONCAT("a"^^xsd:string, "b"^^xsd:string) -> "ab"^^xsd:string
   CONCAT("a", "b") -> "ab"
   CONCAT("a"^^xsd:string, "b") -> "ab"^^xsd:string (?? choice point)
   CONCAT("a"@en, "b"@fr) -> error? (choice point [*])
   CONCAT(str("a"@en), str("b"@fr)) -> "ab"

[*] lang tag support in comparisons etc is not required by base SPARQL 
so it's an error. The question is whether to provide guidance to 
implementations that wish to provide it.

Whether the choice is by new URIs for the functions or punning on XSD 
F&O is part of this decision point.


Suggestion:
1/ Keywords as below.  No dateTime functions.
2/ sparqlfn: URIs for all function (our namespace and URIs)
3/ Definition as XSD F&O except work on simple literals as noted.
4/ Documentation reference XSD F&O for each function.

I am not particularly fond is this way forward nor strongly advocating 
it.  It's a concrete proposal to move the discussion to a conclusion, I 
hope.

	Andy



Numeric functions:

         6.4.1 fn:abs
ABS
         6.4.2 fn:ceiling
CEIL
         6.4.3 fn:floor
FLOOR
         6.4.4 fn:round
ROUND
         6.4.5 fn:round-half-to-even
??
Note precision argument.
Drop?
See discussion at:
http://www.w3.org/TR/xpath-functions/#func-round-half-to-even

String functions:

         7.3.2 fn:compare
? Not needed as a keyword.
         7.4.1 fn:concat
CONCAT
         7.4.3 fn:substring
Two forms /2 and /3
SUBSTRING
Note it's one-based counting and it's (index, length) unlike some languages.

         7.4.4 fn:string-length
LENGTH
         7.4.7 fn:upper-case
UCASE
         7.4.8 fn:lower-case
LCASE
         7.4.10 fn:encode-for-uri
ENCODE
Note it's ENCODE(string) -> string

         7.5.1 fn:contains     (collation form optional)
CONTAINS
No collation form as required SPARQL function.

         7.5.2 fn:starts-with
STARTS
         7.5.3 fn:ends-with
ENDS

DateTime functions:
? Drop
? Or what naming

         10.4.6 op:dateTime-equal
         10.4.7 op:dateTime-less-than
         10.4.8 op:dateTime-greater-than
         10.5.7 fn:year-from-dateTime
         10.5.8 fn:month-from-dateTime
         10.5.9 fn:day-from-dateTime
         10.5.10 fn:hours-from-dateTime
         10.5.11 fn:minutes-from-dateTime
         10.5.12 fn:seconds-from-dateTime
         10.5.13 fn:timezone-from-dateTime

Misc functions:

	3. fn:error
ERROR()
ERROR(string)
Received on Wednesday, 24 November 2010 15:21:00 GMT

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