[DFDL-WG] Fw: Proposal - simplifying opaque types
Suman Kalia
kalia at ca.ibm.com
Thu Aug 16 07:54:20 CDT 2007
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
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