[DFDL-WG] Fw: Action 167: textNumberPatterns with P, V, # - allowable combinations

Thu Mar 22 07:04:58 EDT 2012

Further to discussion on the call, here is what IBM COBOL manual says 
about PIC P.

An assumed decimal scaling position. It is used to specify the location of 
an assumed decimal point when the point is not within the number that 
appears in the data item. The scaling position character P is not counted 
in the size of the data item. Scaling position characters are counted in 
determining the maximum number of digit positions (63) in numeric-edited 
items or in items that appear as arithmetic operands. The scaling position 
character P may appear only as a continuous string of Ps in the leftmost 
or rightmost digit positions within a PICTURE character-string. Because 
the scaling position character P implies an assumed decimal point (to the 
left of the Ps, if the Ps are leftmost PICTURE characters; to the right of 
the Ps, if the Ps are rightmost PICTURE characters), the assumed decimal 
point symbol, V, is redundant as either the leftmost or rightmost 
character within such a PICTURE description. 
In certain operations that reference a data item whose PICTURE 
character-string contains the symbol P, the algebraic value of the data it
em is used rather than the actual character representation of the data 
item. This algebraic value assumes the decimal point in the prescribed 
location and zero in place of the digit position specified by the symbol P
. The size of the value is the number of digit positions represented by 
the PICTURE character-string. These operations are any of the following: 
Any operation requiring a numeric sending operand. 
A MOVE statement where the sending operand is numeric and its PICTURE 
character-string contains the symbol P. 
A MOVE statement where the sending operand is numeric-edited and its 
PICTURE character-string contains the symbol P and the receiving operand 
is numeric or numeric-edited. 
A comparison operation where both operands are numeric. 
In all other operations the digit positions specified with the symbol P 
are ignored and are not counted in the size of the operand. 

This implies that the scaling should be applied as a lexical operation on 
the data. In other words two COBOL fields, one with PIC PP9 and value '2' 
and one with PP999 and value '002' do not result in the same logical 
number.
There is an equivalence between V and P.  PP999 == V99999 and 999PP == 
99999V == 99999.  If we consider things in these terms the reasoning is 
simpler.  To prevent # symbol zero suppression from changing the value, 
rule a) must apply and there must be no # to the right of the V.  That 
restates our rules as:

a) A pattern with a V symbol must not have # symbols to the right of the V 
symbol.

b) A pattern with P symbols at the left end must have no # symbols in the 
pattern. 

c) A pattern with P symbols at the right end has no restrictions.

There is another problem though. The number can be trimmed using the pad 
character from either or both ends depending on justification, before 
applying the number pattern. If the pad character is 0 then this can also 
cause 0's to be lost and result in mis-application of V and P symbols. I'm 
not sure there is much we can do about this.  Modelers need to be careful 
when padding/trimming that they get the justification correct. For 
example, we typically think of numbers as being right justified, but for a 
number with Ps on the left, it is effectively left justified and should be 
modeled as such.  We added errata 2.25 which prevented trimming from 
leaving an empty string. I am thinking that this errata should actually 
say that trimming must leave at least the minimum number of digits implied 
by the pattern, as an extra safeguard?  We mustn't disallow 
trimming/padding altogether as it is used to remove spaces.
The ICU pad character symbol * is used to provide a pad character when the 
data is shorter than the pattern. This is only used to pad when unparsing, 
it is not used to trim. But it might be safer to disallow P and V symbols 
when * is used? 
Reading the ICU description of significant digit symbol @, explicit 
decimal points are disallowed. I think we should disallow P and V symbols 
when @ symbol is used. Errata 2.28 should be updated.
Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
----- Forwarded by Steve Hanson/UK/IBM on 22/03/2012 09:22 -----

From:   Steve Hanson/UK/IBM
To:     dfdl-wg at ogf.org
Date:   21/03/2012 10:34
Subject:        Action 167:  textNumberPatterns with P,V, # - allowable 
combinations

Last week we agreed that disallowing text number patterns that contained a 
# symbol and either a P or V symbol was too restrictive. Accordingly the 
following rules are proposed to control when # may be used in the same 
pattern as P or V to ensure an unambiguous pattern.

a) Pattern must not have # symbols to the right of the V symbol.

b) If pattern has P symbols at the left end, then there must be as many 0 
symbols adjacent to the rightmost P symbol as there are P symbols.

c) If pattern has P symbols at the right end, there are no restrictions.

If a) or b) are violated it is a schema definition error.

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848

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Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU

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