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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