[DFDL-WG] Fw: OGF DFDL WG call today 2007-11-21
kalia at ca.ibm.com
Wed Nov 21 11:01:16 CST 2007
Some interesting discussion on the hexBinary and base64Binary.. Schema
authors also had reservations on having these 2 types with same value
space and considered a possibility of having one binary type with encoding
facet to specify hex and base64 which would have been a much better
solution. I am equally perplexed on the use case for having pattern (and
also enumeration) facet on the hexBinary and base64Binary as the facet
work on the lexical space.
May be the conservative approach for us is to treat these built-in schema
type as is and only allow the dfdl set of annotations pertaining to
By copy to Sandy - do you know of a use case where pattern facet is used
on hexBinary and base64Binary
Some excerpts from discussion
There are two possible ways to fix this before going to
1. return to the CR status of a binary
datatype with an
encoding facet that could be either 'hex' or 'base64'.
2. eliminate one of hexBinary or
base64Binary, and call the
remaining type 'binary'. *Note that this is the most conservative
decision*. The missing encoding could always be added back, but once
released as an official recommendation parsers would be required to
support both encodings for all time.
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools
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Internet ID : kalia at ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 11/21/2007 11:50 AM -----
Mike Beckerle <beckerle at us.ibm.com>
Sent by: dfdl-wg-bounces at ogf.org
11/21/2007 11:08 AM
dfdl-wg at ogf.org
[DFDL-WG] OGF DFDL WG call today 2007-11-21
We may or may not achieve quorum today because of the US holiday tomorrow
and big travel day today.
I will join the call at 12noon US.ET, and if we have enough people by
12:05 then I'd like to discuss one or more of these topics
* hexBinary and base64Binary - I still find these confusing.
* array prefix and suffix - just review resolution of this issue - leaving
out for now just to be conservative. Could put back in fairly easily.
* choiceType and length properties on xs:choice
My latest musings on hexBinary and base64Binary ....
E.g., XSD allows pattern and enumeration facets on these
<element name="aThing" type="base64Binary" length="3"
I think that pattern is a regexp for a base64 string matching 3 bytes of
zeros or 3 bytes of all ones, but my regexp syntax is no doubt incorrectly
escapified. ("A" is 6 bits of zero, "/" is 6 bits of 1 in base64).
To me this is marvelously confusing. It feels downright silly to allow
pattern and enumeration on these things.
I'd like to adopt the strictest possible sensible thing.
- hexBinary only, binary representation only, no pattern or enumeration
facets supported or allowed for this type.
There is still the issue of default/fixed.
<element name="unknownStuff" type="hexBinary" fixed="F41306C0"
The user specifies what the bytes are as a hex string, and since they said
it's hexBinary, they use hex to express the literal content. This is a way
to say "right here in the data there's this blob of stuff I don't
understand, but it always contains these data bytes". I've certainly seen
the need for this sort of thing. It's being ignored on input, but on
output it generates the fixed bytes of data so as to create valid output
even when you don't understand this part of the data format. In fact, the
cases I've seen are using this to skip over decimal numbers the wierd
format of which isn't understood. The above pattern could be one or more
decimal numbers in strange formats.
However, I can see the slippery slope from here to allowing pattern and
enumeration facets, so I'd be happy ruling out use of default and fixed on
hexBinary type also, just to make it even simpler.
Also, this element achieves the same end using our "%" escapes in strings.
<element name="unknownStuff" type="string" dfdl:encoding="ascii"
This works for any single-byte-wide character-set encoding.
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
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