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@uk.ibm.com
Phone (+44)/(0) 1962-815848


Mike Beckerle <beckerle@us.ibm.com>
Sent by: dfdl-wg-bounces@ogf.org

16/11/2007 23:09

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dfdl-wg@ogf.org
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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@us.ibm.com
                508-599-7046
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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