I am way out of the loop here, but I felt motivated to throw in a few cents on this discussion.

As far as scope goes, it seems to me a reasonable goal to consider would be to include all the primitive types of XML Schema as in scope. That would suggest that hexBinary and base64 should be included.

Regarding implementation, what concerns me about the discussion is the confusion between data model and representation that I seem to be hearing. (Perhaps I am bringing this to the discussion in which case please set me straight).

The way it looks to me is that when you specify the XML Schema “type” in the DFDL document you are specifying the data model, or another way to put it is that you are specifying the form of the XML document that would be output if your DFDL parser were producing a document. This should be separated from the discussion of the representation of the data that you are reading in.

So what I expect is that there are three different data models for this kind of data:

Sequence of bytes
hexBinary
base64

And there are three different underlying representations of the data that could be read from:

bytes
bin hex
base 64

And ideally you should be able to choose the model and the data separately (IMO).

Am I making sense?

Martin

From: dfdl-wg-bounces@ogf.org [mailto:dfdl-wg-bounces@ogf.org] On Behalf Of Mike Beckerle
Sent: Monday, November 19, 2007 8:34 AM
To: Steve Hanson
Cc: dfdl-wg@ogf.org
Subject: Re: [DFDL-WG] DFDL hexBinary and base64Binary

Steve, (& team)

What you are suggesting is the simplest of the simple. No 'text' representation at all, Users who have actual hexidecimal strings in their data can always model them as either strings or if they're small enough, integers in base 16 text.

In this case the only difference between hexBinary and base64Binary is what happens if you coerce the infoset value to a string and this is into the API space which is outside the scope of DFDL.

To me this suggests that we leave out base64Binary entirely for V1.0 to avoid confusion (it will be confusing to people to explain that hexBinary and base64Binary are synonymous in DFDL)

So the net functionality for DFDL v1.0 would be this only:

*type*	*representation*	*lengthKind*	*resulting length (in bytes)*	*other*
xs:hexBinary	binary (note: required - If 'text' specified it causes a schema definition error. This reserves the 'text' behavior for possible future use.)	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	Validation: xs:length facet must be equal to resulting length in bytes (TBD: similar range checks on xs:minLength, xs:maxLength)

I'm very happy with this for V1.0.

Any further comments or should we go with this for V1.0?

...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

Steve Hanson <smh@uk.ibm.com>
Sent by: dfdl-wg-bounces@ogf.org

11/19/2007 10:23 AM

To	dfdl-wg@ogf.org
cc
Subject	Re: [DFDL-WG] DFDL hexBinary and base64Binary

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

To	dfdl-wg@ogf.org
cc
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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