[DFDL-WG] Fw: DFDL: TLOG proposal

[Steve Hanson]

Updated below as agreed on DFDL WG call Jan 29th.

Regards

Steve Hanson
Programming Model Architect, WebSphere Message Broker,
OGF DFDL WG Co-Chair,
Hursley, UK,
Internet: smh at uk.ibm.com,
Phone (+44)/(0) 1962-815848
----- Forwarded by Steve Hanson/UK/IBM on 29/01/2010 17:40 -----

From:
Steve Hanson/UK/IBM
To:
dfdl-wg at ogf.org
Date:
26/01/2010 12:26
Subject:
DFDL: TLOG proposal



TLOG
The individual fields are a mixture of ASCII strings, proprietary packed 
decimals, and the occasional pure binary data. All fields are delimited by 
a separator. Fields of all types can be fixed length or variable length 
with a maximum. Pure binary data is preceded by a field giving the actual 
length. All lengths in bytes. 

Packed decimals. Like a packed decimal in the IBM sense. These can carry 
negative numbers but use a leading xD sign nibble. No sign nibble if 
positive or unsigned. Odd number of digits (including sign if present) are 
padded with xF nibble. This is best illustrated using examples. 
1234     =>     x12x34 
123      =>     xF1x23 
-1234    =>     xFDx12x34 
-123     =>     xD1x23 

Proposal
1) The 'variable length with a maximum' will be handled using a 
post-timing assertion. Note this only applies on parsing. **

2) dfdl:lengthKind 'delimited' is permitted for numbers when 
dfdl:representation is 'binary' and dfdl:binaryNumberRep is 'packed' or 
'bcd' because it is possible to know in advance the range of bytes being 
used, and therefore to choose suitable delimiters.

3) Core DFDL 1.0 will not be enhanced to handle the TLOG packed decimal 
type.  A future version of DFDL will provide an extensibility mechanism 
that allows user-defined types to be handled.  In the 1.0 timeframe IBM 
may implement its own proprietary extension to handle this type. 

** While this can result in output from a DFDL unparser that can not be 
re-parsed, that is a problem general to the use of assertions, and a 
future version of DFDL may choose to change this by enhancements to the 
assertion annotation.

Regards

Steve Hanson
Programming Model Architect, WebSphere Message Broker,
OGF DFDL WG Co-Chair,
Hursley, UK,
Internet: smh at uk.ibm.com,
Phone (+44)/(0) 1962-815848





Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU












Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU





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