[DFDL-WG] DFDL: Minutes from OGF WG call, 20 Feb 2008
Ian W Parkinson
PARKIW at uk.ibm.com
Thu Feb 21 09:41:09 CST 2008
Open Grid Forum: Data Format Description Language Working Group
Weekly Working Group Conference Call
17:00 GMT, 20 Feb 2008
Attendees
Steve Hanson (IBM)
Suman Kalia (IBM)
Ian Parkinson (IBM)
1. Discriminators
Suman had proposed, via email, that forward references be allowed in
discriminator expressions. This would make some DFDL schemas clearer by
allowing the discriminator to reside on the element immediately beneath
the "choice" construct, rather than on whichever subelement the
discrimator uses. However it is simpler to just disallow forward
references. Steve and Suman agreed to leave forward references disallowed
for the time being, and to see what feedback is received from adopters.
The group had previously noted that no timing property is defined on
discriminators, as they are for asserts, and Steve raised the question,
suggesting that it had perhaps been deliberately omitted when
discriminators were introduced as an alternative to allowing an assert to
optionally discriminate a choice. Ian observed that if a parse error
occurs while parsing an element, then the choice cannot resolve to the
affected branch; so we can always evaluate discriminators after parsing
the element defining the discriminator. Any parse error would result in a
backtrack. We should document the behaviour of discriminators more clearly
in the specification.
Suman suggested it would be useful to add discriminators automatically,
when converting a COBOL copybook, C structure, etc. to DFDL.
2. Abstract data model
Steve was hoping that the UML diagrams would allow a DFDL user to quickly
and easily see whch subset of XSD is used by DFDL. With this in mind he'd
like to fnd a way to simplify the current proposed diagrams, and will
think further on this and contact Simon.
3. Entities
With his most recent DFDL entities proposal, Alan had asked whether we
should support standard XML entities - something which is not listed in
the DFDL specification. As entities are defined by XML and not by XML
Schema, we are not at liberty to disallow standard XML entities from a
DFDL schema. Indeed, there is no obvious reason to disallow these entities
in any case.
Meeting closed, 17:30 GMT
Ian Parkinson
WebSphere ESB Development
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