[jsdl-wg] (Param sweep) Proposed updated looping text

[geoff]

Hi all,

In addition to the other requested specification modifications ("lay 
dog"s and XPath 1+2) please take a look at the proposed looping 
modifications.

Frustratingly one issue still remains: Dave Meredith has raised the 
prospect of problems if we advise the use of ranges when performing 
LoopDouble Exception comparison as effectively it's a green light for 
inconsistency across implementations (and in some respects 
mismatching/inaccuracy). As we're strongly recommending the adoption of 
the IEEE 754 standard decimal floating point arithmetic in 
implementations I think that this should provide the expected 
consistency (even if it's consistent inaccuracy!?) without the need for 
ranges. Alternatively a reversal on my earlier hesitation in the 
adoption of the jsdl:RangeValue_Type may be required, e.g.

> <sweepfunc:LoopDouble substitutes=”sweep:Function”
>                 start=”xsd:double”
>                 end=”xsd:double”
>                 step=”xsd:double” >
>     <sweepfunc:Exception> jsdl:RangeValue_Type </sweepfunc:Exception>*
> </sweepfunc:LoopDouble>

gef

------------------------------------------

4.2 LoopInteger function

The LoopInteger function provides an ordered list of integer values 
within the inclusive range specified by the start and end values.  The 
list begins at the start value and contains all subsequent rangebound 
incremented or decremented values as determined by the step value.

A LoopInteger function MAY exclude certain values by including Exception 
Child elements.

This function yields values that are calculated as follows. The first 
value equals the value of the start value. Any subsequent value is 
calculated using the following rule:

     nextValue ::= currentValue + valueOf( step )

If “nextValue” is beyond the range boundary specified by the end value, 
then “nextValue” is discarded and the LoopInteger function terminates 
with “currentValue”. If a value for “step” is not given, the default 
value of “1” MUST be used.

... [unmodified]

Implementations handling the LoopInteger function may choose to :
   - Where possible, predetermine and validate the loop cardinality by 
inspection prior to running the loop operation, and confirm cardinality 
post-operation.
   - Respond appropriately if schematically valid yet questionable 
values are supplied, e.g. if the value 0 is encountered for step.

... [unmodified]

4.3 LoopDouble function

The LoopDouble function provides an ordered list of double datatype 
values (corresponding to the IEEE double-precision 64-bit floating point 
type) within the inclusive range specified by the start and end values. 
  The list begins at the start value and contains all subsequent 
rangebound incremented or decremented values as determined by the step 
value.

... [unmodified]

The permissible value range...
....The following are therefore considered valid xsd:double values : 
-1E4, 1267.43233E12, 12.78e-2, 12, NaN, -0 and INF .

Please note (accuracy advice): The reference to xsd:double datatype 
values (and double-precision 64-bit floating point types) is solely for 
the definition of the valid value range and format acceptable in 
LoopDouble functions.  Implementations which process such values should 
have functionality that most accurately interprets and operates on such 
a value range and format, e.g. it is strongly recommend that 
implementations support IEEE 754 standard [1] decimal (base 10) floating 
point arithmetic, in preference to binary (base 2) arithmetic.

Implementations handling the LoopDouble function may choose to :
  - Where possible, predetermine and validate the loop cardinality by 
inspection prior to running the loop operation, and confirm cardinality 
post-operation.
  - Convert xsd:double datatype values to integer values and implement 
only integer arithmetic processing.
  - Determine an acceptable range when comparing equality of a 
particular loop value against loop Exception values, e.g. an exception 
may be affirmed if a loop Exception value is within a % range of the 
loop value.
  - Encourage consistency in value format, e.g. avoid mixing scientific 
and non-scientific nomenclature in a LoopDouble element.
  - Respond appropriately should schematically valid yet questionable 
values such as NaN, -0, INF, -INF be encountered.


Footer note:
[1] IEEE 754 - 2008 http://ieeexplore.ieee.org/servlet/opac?punumber=4610933