[DFDL-WG] DFDL: Minutes from OGF WG call, 06 Feb 2008

[Ian W Parkinson]

Open Grid Forum: Data Format Description Language Working Group

Weekly Working Group Conference Call
17:00 GMT, 06 Feb 2008


Attendees
Steve Hanson (IBM)
Geoff Judd (IBM)
Simon Parker (PolarLake)
Ian Parkinson (IBM)
Alan Powell (IBM)

Apologies
Mike Beckerle (Oco)
Suman Kalia (IBM)


1. Review of the draft DFDL Schema Abstract Model

Simon has distributed, via the DFDL working group mailing list, a draft of 
the UML description of the DFDL schema components, with diagrams built 
from scratch but using concepts from a number of different, public, UML 
descriptions of XML schema. The meeting reviewed and discussed this draft.

'Particle' diagram
Steve noted that the diagram has changed some of the object names. Simon 
agreed that he expected some of these to revert to standard XML 
nomenclature - but that some concepts don't have an existing naming 
convention.
The diagram allows for "all" groups - which are not supported in DFDL. 
This is as specified in section 5.1 of the present DFDL specification 
draft.
The diagram shows "Group" as a subclass of "GroupDefinition". The XML 
schema specification does appear to allow this, but the meeting agreed 
this should be removed from the diagram.
Steve and Geoff suggested that GlobalElement should be modelled as a 
subclass of ElementDeclaration.

'Type' diagram
The diagram distinguishes between GlobalType and TypeDefinition, to allow 
GlobalTypes to be named while TypeDefinitions remain anonymous.
The 'base' relationship should be between TypeReference and SimpleType, 
not between TypeReference and TypeDefinition. Complex type inheritence is 
not allowed by DFDL.
After consulting the schema specification, Steve withdrew his suggestion 
that ComplexType should contain a ModelGroup rather than a Particle. Simon 
pointed out that XML Schema 1.1 will allow particles to take annotations, 
which may prove useful for DFDL.

'DFDL Annotations' diagram
Hidden elements are wrapped inside DFDL annotations. This allows for a 
DFDL schema to be mapped to an XSD schema by stripping all DFDL 
annotations; the resulting XSD schema describing a DFDL InfoSet for the 
DFDL schema. This is a goal of DFDL.

Alan asked about the purpose of these digrams. They are intended to model 
and communicate the valid subset of XML schema, and also show where DFDL 
annotations can be placed in a DFDL schema. We could also use these 
diagrams to model which XSD objects each DFDL property affects, as well as 
showing where the properties may be defined - however Simon felt that as a 
property is not itself a DFDL annotation, this information is better 
documented elsewhere.

Steve felt that the diagrams included in this draft are overcomplicated, 
and wondered if we could reduce the number of boxes in the diagrams, for 
example by removing the distinction between named and anonymous objects. 
Simon observed that this is an important distinction for DFDL as, for 
example, named types may be reused in different contexts, and this 
distinction allows us to describe how properties apply differently to 
named and anonymous types. With this in mind, the diagrams are as simple 
as possible.


2. Other business

Alan will incorporate the UML diagrams, along with the other planned 
specification updates, into a new draft of the specification to be 
distributed on the 7th Feb.


Meeting closed, 18:00 GMT



Ian Parkinson
WebSphere ESB Development
Mail Point 211, Hursley Park, Hursley, Winchester, SO21 2JN, UK





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