Tim
'Optional occurrence' is already defined
in the Glossary with a different meaning.
I've spent some time thinking through
this issue again, and I'd prefer not to say that this is a processing error.
Although net effect is the same we have to be very careful that the words
here are consistent with section 9. Note that we don't have to worry about
known-not-to-exist (missing/absent) as this terminates the array anyway
by definition. The circumstance we are really discussing here is known-to-exist.
16.6 Forward Progress Requirement
The parsing of an array that is potentially unbounded terminates when the
position in the data does
not move during the parsing of an occurrence that is a point of uncertainty
(including any associated Separator, PrefixSeparator or PostfixSeparator
region), even if the occurrence is known-to-exist. This is to prevent an
infinite loop. An array is potentially unbounded if any of the following
are true:
* dfdl:occursCountKind is 'stopValue'
* dfdl:occursCountKind is 'parsed'
* dfdl:occursCountKind is 'implicit' and XSDL maxOccurs is unbounded
When dfdl:occursCountKind 'stopValue'
this results in a processing error because the stop value will never be
encountered.
Note: When dfdl:occursCountKind is
'implicit' and XSDL maxOccurs is not unbounded, and the position
in the data does not move during the parsing of an occurrence that is a
point of uncertainty (including any associated Separator, PrefixSeparator
or PostfixSeparator region), and the occurrence is known-to-exist, and
the occurrence does not give rise to a value in the infoset, implementations
may terminate the parsing of the array. This is to prevent the unnecessary
consumption of resources for large values of XSDL maxOccurs.
Note that the last (bounded) paragraph
above goes back on what we said about nil representation. For consistency
with section 9, nil should not terminate the array. This might result in
excessive resource consumption, but that is necessary to create the infoset
implied by the schema.
Regards
Steve Hanson
Architect, IBM Data Format Description Language (DFDL)
Co-Chair, OGF
DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848
From:
Tim Kimber/UK/IBM@IBMGB
To:
dfdl-wg@ogf.org,
Date:
29/01/2014 15:12
Subject:
[DFDL-WG] Fw:
Spec question: 16.6 Forward Progress Requirement
Sent by:
dfdl-wg-bounces@ogf.org
Proposed revised wording:
16.6 Forward Progress Requirement
When parsing an optional occurrence of an array element, if the element
is found to have a zero-length representation and its associated separator
region is also zero-length then it is a processing error.
An optional occurrence is defined as follows:
- any occurrence of an element with occursCountKind='implicit' and index
> XSDL minOccurs
- any occurrence of an element with occursCountKind='parsed' or 'stopValue'
If occursCountKind is 'stopValue' then the element will not be a point
of uncertainty and the processing error will invalidate the entire array.
For occursCountKind='implicit' or 'parsed' the processing error will terminate
the array and will thus avoid either redundant processing or an infinite
loop ( when XSDL maxOccurs='unbounded').
Feel free to propose better terminology. I'm not sure whether 'optional
occurrence' has been used elsewhere in the specification with a different
meaning.
The final paragraph is conveying important information but can be reworded
if necessary.
regards,
Tim Kimber, DFDL Team,
Hursley, UK
Internet: kimbert@uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
----- Forwarded by Tim Kimber/UK/IBM on 29/01/2014 14:42 -----
From: Tim
Kimber/UK/IBM
To: dfdl-wg@ogf.org,
Date: 28/01/2014
14:24
Subject: Spec
question: 16.6 Forward Progress Requirement
16.6 Forward Progress Requirement
It is a processing error when an array is potentially unbounded and the
position in the data does
not move during the parsing of an occurrence of the element including any
associated separator.
This is to prevent an infinite loop. An array is potentially unbounded
if any of the following are
true:
* dfdl:occursCountKind is 'parsed' or 'stopValue'
* dfdl:occursCountKind is 'implicit' and XSDL maxOccurs is 'unbounded'
Q1: Is this paragraph intended to
a) safely terminate the parsing of the array, allowing the parser to proceed
with whatever follows in the DFDL schema or
b) cause the parser to discard the entire array along with everything that
was parsed within the nearest point of uncertainty?
If b) then I think a Schema Definition Error would be more appropriate
( because backing out the entire array implies that none of the occurrences
were well-formed and some later branch might be the correct option ). Although...
Q2: If the array has occursCountKind='stopValue' then none of the occurrences
is an actual point of uncertainty because only stopValue can terminate
the array. If paragraph 16.1 is invoked then a processing error will be
thrown. But the occurrence is not a point of uncertainty so the entire
array will be treated as badly-formed. In other words, behaviour will be
as described in option b) above. I think that is correct in this case because
the array's stopValue was never found.
Q3: Should this infinite-loop detection be performed only after at least
minOccurs occurrences of the array have been processed successfully? Until
then, I think an empty occurrence should cause the default value to be
put into the info set.
regards,
Tim Kimber, DFDL Team,
Hursley, UK
Internet: kimbert@uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
3AU
Unless stated otherwise above:
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741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
3AU--
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