[DFDL-WG] DFDL hexBinary and base64Binary

Mon Nov 19 09:23:18 CST 2007

My view: The logical type is binary, so the data in the information item 
is binary, the length facets should always deal in bytes, and validation 
checks the length of the binary data in bytes.

From the above, of the two simplifications below, I would rather disallow 
the text representations of xs:hexBinary and xs:base64Binary. Fyi MRM 
today 
- does not support text reps for binary 
- has not had such a request from users 
- uses length/minLength/maxLength facets to validate binary field length 
post-parse
- uses length/maxLength to populate the default for the physical length. 

Regards, Steve

Steve Hanson
WebSphere Message Brokers
Hursley, UK
Internet: smh at uk.ibm.com
Phone (+44)/(0) 1962-815848

Mike Beckerle <beckerle at us.ibm.com> 
Sent by: dfdl-wg-bounces at ogf.org
16/11/2007 23:09

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Subject
[DFDL-WG] DFDL hexBinary and base64Binary

I'm trying to wrap up the opaque/hexBinary/base64Binary topic. 

I need opinions on this discussion. 

Currently we have a property, dfdl:binaryType : 

Properties Specific to Binary Types (hexBinary, base64Binary) 
Property Name 
Description 
binaryType 
Enum 
This specifies the encoding method for the binary.   
Valid values are ‘unspecified’, ‘hexBinary’, ‘base64Binary’, ‘uuencoded’ 
Annotation: dfdl:element (simple type ‘binary’, ‘opaque’)

This property speaks to what kinds of representations can we interpret and 
construct logical hexbinary values from? (similarly base64Binary) 

I believe the above is not clear, and causes issues with the xs:length 
facet of XSD. 

I propose the 4 tables below which describe the 4 cases: 

hexbinary - binary 
hexbinary - text 
base64binary - binary 
base64binary - text 

I have specified these so that the meaning of the xs:length facet is 
always interpreted exactly as in XSD. It always refers to the number of 
bytes of the unencoded binary data, and never to the number of characters 
in the encoded form. 

type
representation
lengthKind
resulting length (in bytes)
other
xs:hexBinary 
binary 
implicit 
xs:length facet 

explicit 
dfdl:length 
Validation: xs:length facet must be equal to resulting length in bytes   
(TBD: similar range checks on xs:minLength, xs:maxLength) 

endOfData or delimited or nullTerminated 
variable 

type
representation
lengthKind
resulting length (in characters)
other
xs:hexBinary 
text 
implicit 
2 * xs:length facet 

explicit 
dfdl:length 
Validation: xs:length facet  * 2 must be equal to resulting character 
length (after removing all non-hex characters) 
 (TBD: similar range checks on xs:minLength, xs:maxLength) 

endOfData, delimited, nullTerminated 
Variable 

type
representation
dfdl:lengthKind
resulting length (in bytes)
other
xs:base64Binary 
binary 
implicit 
xs:length facet 

explicit 
dfdl:length 
Validation: xs:length facet must be equal to resulting length in bytes 
(TBD: similar range checks on xs:minLength, xs:maxLength) 

endOfData or delimited or nullTerminated 
variable 

type
representation
lengthKind
resulting length (in characters)
other
xs:base64Binary 
text 
implicit 
8/6 * xs:length facet 

explicit 
dfdl:length 
Validation: xs:length facet  *  8/6 must be equal to resulting character 
length (after removing all non-base64-encoding characters) 
(TBD: similar range checks on xs:minLength, xs:maxLength) 

endOfData, delimited, nullTerminated 
Variable 

Looking at the above, one way to simplify things quite a bit is to 
disallow the xs:length and xs:minLength and xs:maxLength  facet on 
hexBinary and base64Binary types in DFDL schemas. 
Then the implicit lengthKind goes away, and the complex validation check 
for the xs:length facet goes away.  I recommend this. 
Another simplification alternative is to disallow representation text 
altogether, but I am concerned that peopel with data that does contain hex 
or base64 data will naturally want to use these types to model it.  I 
don't recommend this. 
...mikeb 
Mike Beckerle
STSM, Architect, Scalable Computing
IBM Software Group
Information Platform and Solutions
Westborough, MA 01581
direct: voice and FAX 508-599-7148
assistant: Pam Riordan 
                 priordan at us.ibm.com 
                 508-599-7046
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