[DFDL-WG] Hidden elements - summary of approaches

[Steve Hanson]

Let's state the two options being considered, as I said I'd do this for 
the wider DFDL WG for the call today:

1) Global group approach 
Summary:
Particle to hide can be a local element, element ref, local sequence, 
local choice or group ref
Particle is removed from its parent into a dedicated global group of 
composition sequence and replaced in the parent by a new empty local 
sequence
The new empty local sequence carries a dfdl:hidden annotation that has a 
property dfdl:groupRef, other DFDL properties are not allowed
Alternatively, the new empty local sequence carries a dfdl:hiddenGroupRef 
property, other DFDL properties are not allowed
Pros:
Removal of all DFDL annotations and use of the resultant pure XSD results 
in same infoset
Global group can be reused
Cons:
Making something hidden is a refactor operation
Global group sequence needs DFDL properties setting correctly

2)  Hidden flag approach
Summary:
Particle to hide can be a local element, element ref
Particle takes a dfdl:hidden property 
xs:minOccurs MUST be 0
A dfdl:minOccurs property takes the place of xs:minOccurs.
Pros:
Easy to make something hidden 
Cons:
Removal of all DFDL annotations and using pure XSD does not guarantee the 
same infoset
Breaks validation
Duplication of minOccurs property 
Have to wrap a local sequence, choice or group ref in a complex element in 
order to hide it (they can't take minOccurs = 0)

Regards

Steve Hanson
Strategy, Common Transformation & DFDL
Co-Chair, OGF DFDL WG
IBM SWG, Hursley, UK,
smh at uk.ibm.com,
tel +44-(0)1962-815848







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