[DFDL-WG] Action 081: Clarification of NaN and Inf

[Alan Powell]

DFDL support for Infinity and Nan need clarification. There are two 
aspects

Representation of infinity and Nan in the infoset 
Representation of Infinity and Nan in the datastream


Representation of infinity and Nan in the infoset 

DFDL should follow XML which allows +inf, -inf and Nan for Float and 
Double

>From XML Schema Part 2: Datatypes Second Edition

[Definition:]  float is patterned after the IEEE single-precision 32-bit 
floating point type [IEEE 754-1985]. The basic ·value space· of float 
consists of the values m × 2^e, where m is an integer whose absolute value 
is less than 2^24, and e is an integer between -149 and 104, inclusive. In 
addition to the basic ·value space· described above, the ·value space· of 
float also contains the following three special values: positive and 
negative infinity and not-a-number (NaN). The ·order-relation· on float 
is: x < y iff y - x is positive for x and y in the value space. Positive 
infinity is greater than all other non-NaN values. NaN equals itself but 
is ·incomparable· with (neither greater than nor less than) any other 
value in the ·value space·. 

The special values positive and negative infinity and not-a-number have 
lexical representations INF, -INF and NaN, respectively. Lexical 
representations for zero may take a positive or negative sign.  

Similarly description for Double

Minor changes to infoset [dataValue] description

1.      [dataValue] The value in the value space (as defined by XML Schema 
Part 2: Datatypes [XSDLV1] ) of the [datatype] member  or special value 
nil. In a complex element information item this member has no value. For 
information items of datatype xs:string, the value will be the  ISO10646 
character codes of the string and 'implicit' (also known as logical), 
left-to-right bidirectional ordering and orientation. 

Is it sufficient just to refer to XML schema rather than spell out the 
value spaces in this specification?


Representation of Infinity and Nan in the data stream

ICU allows a single character for Nan and infinity. The infinity character 
can be prefixed by the positive or negative prefix (ie the prefix part of 
he pattern)

This is too restrictive for DFDL as we need to be able to support at least 
 'INF' '-INF' and 'NaN'


Only minor changes to current description.


numberInfinityRep
String
The value used to represent infinity.
Infinity is represented as string with the positive or negative prefixes 
and suffixes from the numberPattern applied
This property is applicable when dfdl: textNumberRepresentation is 
'standard' and the simple type  type is float or double.
Annotation: dfdl:textNumberFormat
numberNaNRep
String
The value used to represent NaN.
NaN is represented as string and the positive or negative prefixes and 
suffixes from the numberPattern are not used
This property is applicable when dfdl: textNumberRepresentation is 
'standard' and the simple type type is float or double.
Annotation: dfdl:textNumberFormat

 




Regards

 
Alan Powell
 
Development - MQSeries, Message Broker, ESB
IBM Software Group, Application and Integration Middleware Software
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