[DFDL-WG] Fw: Proposal - simplifying opaque types

[Suman Kalia]

Sorry I could not call-in yesterday as I had conflict with another 
meeting. Here are my comments on the proposal

>>  A byte string is described like this:

>>  <element name=”foo” type=”string” 
>>         dfdl:encoding=”bytes” dfdl:lengthKind=”fixed” 
dfdl:length=”17”/>

I am not sure if dfdl:encoding=byte is the correct way to model opaque 
blob of data which may not be a string but complex structure containing 
mixture of text and binary data and that structure blob may have alignment 
requirements within the memory layout.  I believe the correct way to model 
blob is really the hexBinary or base64binary - these types do describe the 
encoding and by default you would specify the length in terms of number of 
bytes which could be described through length facet. 

The example HexBinary Type provided in section 7.2 

When you model something as hexBinary, it is wrong to say the 
representation is text because data represented through hexBinary may not 
be string at all ( could be a complex structure) and the DFDL 
representations given below in the example would not be correct. The 
example provided by Simon was simple where the data just happened to be 
string data.

>> Suppose we wanted to model this same data logically as a hexBinary 
'blob'.
 >>  <element name="d" type="hexBinary" dfdl:representation="text" 
dfdl:encoding="utf-8" 
dfdl:length="11" 
dfdl:lengthUnitKind="characters"/>


In some respect having dfdl:encoding=byte and making it not sensitive to 
character encoding, we are simulating what hexBinary specifies already.
Question : Why promote an additional DFDL specific construct when it could 
be catered through built-in schema type? 

PS: I am not against having dfdl:encoding=byte as specified in the spec 
but promoting it as a mechanism to model opaque binary data will not rest 
well with XML Schema folks. 


Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools 
Tel : 905-413-3923  T/L  969-3923
Fax : 905-413-4850 T/L  969-4850
Internet ID : kalia at ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 08/16/2007 08:49 AM -----

Mike Beckerle <beckerle at us.ibm.com> 
Sent by: dfdl-wg-bounces at ogf.org
08/10/2007 03:26 PM

To
dfdl-wg at ogf.org
cc

Subject
[DFDL-WG] Proposal - simplifying opaque types







Please review for discussion on a future call. 



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
--
  dfdl-wg mailing list
  dfdl-wg at ogf.org
  http://www.ogf.org/mailman/listinfo/dfdl-wg
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.ogf.org/pipermail/dfdl-wg/attachments/20070816/ace97f5d/attachment-0001.html 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: proposal-to-simplify-opaque-types.doc
Type: application/octet-stream
Size: 45056 bytes
Desc: not available
Url : http://www.ogf.org/pipermail/dfdl-wg/attachments/20070816/ace97f5d/attachment-0001.obj