271
Use of maxOccurs '0' (All)
2/9: Legal in XSDL and DFDL. One use case in XSDL is when deriving a complex type by restriction, where it is used to indicate that an element in the base type must not appear. Another use case could be if a schema undergoes a version revision that removes elements; perhaps clearer if the removed element gets maxOccurs '0' rather than omitting it. Steve has seen an instance of its use in a DFDL schema.
So if DFDL continues to support it, need to document the behaviour for the various occursCountKinds and what happens to separator. Also behaviour of occursCount expression that returns 0. Proposal needed.
...
23/9: No progress

IBM has discussed this internally and has the following proposal. Infoset refers to the augmented infoset.

OCK
maxOccurs '0'
Parsing Unparsing
fixed No occurrences looked for in the data (1) No occurrences looked for in the infoset or written (2)
implicit No occurrences looked for in the data (1) No occurrences looked for in the infoset or written (2)
expression occursCount occurrences expected. If any are found it is a validation error. Any number of occurrences expected in the infoset and written. If any are found it is a validation error.
parsed Any number of occurrences expected in the data. If any are found it is a validation error. Any number of occurrences expected in the infoset and written. If any are found it is a validation error.
stopValue Any number of occurrences expected in the data. If any are found it is a validation error. Any number of occurrences expected in the infoset and written. If any are found it is a validation error.

OCK Parsing and occursCount '0' Unparsing and no occurrences in infoset
expression No occurrences looked for in the data. (1) No occurrences written. (2)


Notes

(1) If sequence has a separator, no separator is looked for in the data when parsing.

(2) If sequence has a separator, no separator is output when unparsing.


Regards
 
Steve Hanson
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848
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