[DFDL-WG] OCK expression and count of 0 for a choice member....
Alex Wood1
WOODA at uk.ibm.com
Mon Apr 27 05:49:33 EDT 2015
Hi Mike,
Can you clarify if you are saying that OCK expression should be prohibited
completely on a choice member (as occurrences for OCK expression are
potentially optional regardless of minOccurs value)
Or is your statement that it should cause an SDE specific to the count==0
case?
Kind Regards,
- Alex
Alex Wood -
Software Engineer -
WebSphere Message Broker Development
DFDL Development
MP 211, IBM UK Labs, Hursley Park, Winchester, Hants. SO21 2JN.
Tel: Internal 246272, External 01962 816272
Notes: Alex Wood1/UK/IBM at IBMGB
e-mail: wooda at uk.ibm.com
From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: Alex Wood1/UK/IBM at IBMGB
Date: 24/04/2015 15:10
Subject: Re: [DFDL-WG] OCK expression and count of 0 for a choice
member....
I think this is an SDE.
Choice branches cannot be optional.
Optional here, does not mean minOccurs == 0, because for many
occursCountKinds, that's never checked unless validation is on, and
validation doesn't guide parsing anyway.
Optional here means "not required by the DFDL format", as in
occursCountKind cannot be 'parsed' at all, because all occurrences are
then not required, and the min/maxOccurs are only examined for validation
purposes, also occursCountKind cannot be 'implicit' for the same reasons,
and occursCountKind 'expression' also.
Wrapping the array element in a sequence doesn't solve the problem unless
the sequence has a required piece of syntax such as an initiator or
terminator, or a hiddenGroupRef to a not-optional (recursively) thing.
Even initiator and terminator are tricky, because in a non-delimited
format, those can be %WSP*; which can match nothing at all; hence, they do
not "require" any syntax.
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
www.tresys.com
Please note: Contributions to the DFDL Workgroup's email discussions are
subject to the OGF Intellectual Property Policy
On Fri, Apr 24, 2015 at 9:07 AM, Alex Wood1 <WOODA at uk.ibm.com> wrote:
Hi All,
Please see below for a history of the issue.
This arose from fuzz testing of the IBM DFDL parser which produced a test
with a coutn of 0 for an OCK expression array which was a choice member.
And subsequent reference to the specification.
It was not clear what the correct outcome should be in a choice where the
first member is an array using OCK expression where the count resolves to
0.
a.) resolve the choice to the zero length array
b.) move to the next choice branch
c.) throw an error
Kind Regards,
- Alex
Alex Wood -
Software Engineer -
WebSphere Message Broker Development
DFDL Development
MP 211, IBM UK Labs, Hursley Park, Winchester, Hants. SO21 2JN.
Tel: Internal 246272, External 01962 816272
Notes: Alex Wood1/UK/IBM at IBMGB
e-mail: wooda at uk.ibm.com
From: Steve Hanson/UK/IBM
To: Alex Wood1/UK/IBM at IBMGB
Cc: Andrew Edwards/UK/IBM at IBMGB, Mark Frost/UK/IBM
Date: 24/04/2015 09:19
Subject: Re: OCK expression and count of 0 for a choice member....
When I wrote the paragraph below, the one thing that troubled me was that
the spec defines known-to-exist and known-not-to-exist in terms of
occurrences. In the choice branch example, it is the element as a whole we
are looking at. That's fine for scalar as element == occurrence but for an
array it's not the same. I think the spec is missing a definition of what
'missing' means for an array element. I would say that an array element is
missing if all occurrences are missing. And an array element is not
missing if any occurrence has a representation (empty, nil, normal). With
that in place, my paragraph makes sense, I think.
I believe we have the same issue with 'parsed' and 'stopValue'.
Regards
Steve Hanson
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
From: Steve Hanson/UK/IBM
To: Alex Wood1/UK/IBM at IBMGB
Cc: Andrew Edwards/UK/IBM at IBMGB, Mark Frost/UK/IBM at IBMGB
Date: 23/04/2015 18:52
Subject: Re: OCK expression and count of 0 for a choice member....
Here is one interpretation...
A choice is resolved by parsing the branches until one is known-to-exist
as described in section 9.3.3. Section 9.3.1.2 defines known-to-exist (in
the absence of a discriminator, initiator or direct dispatch) as an
occurrence having empty, nil or normal representation. Section 9.3.1.3
defines known-not-to-exist (again in the absence of a discriminator,
initiator or direct dispatchm or an assert) as an occurrence being missing
or causing a processing error. If occursCount is zero no occurrences are
looked for in the data (erratum 5.9) so the element has no representation
and must be missing. Therefore a choice branch containing such an element
is known-not-to-exist.
So in your example, the first choice branch containing myInt is
known-not-to-exist and the parser tries the next branch.
This appears to contradict section 15.1.1 though. I suspect that 15.1.1
was not updated to match section 9.3 when the latter was added.
If you want to make the first choice branch known-to-exist when the count
is zero then I think wrapping myInt in a sequence would work. Or wrapping
myInt in a complex element.
Definitely one to take to the WG though, if only to correct section 15.1.1
to match section 9.
Regards
Steve Hanson
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
From: Alex Wood1/UK/IBM
To: Steve Hanson/UK/IBM at IBMGB
Cc: Andrew Edwards/UK/IBM at IBMGB, Mark Frost/UK/IBM at IBMGB
Date: 23/04/2015 16:33
Subject: OCK expression and count of 0 for a choice member....
Hi Steve
Just been discussing this with Andy and Mark.
I think the spec
<xs:element name="Choice_Expression" dfdl:ref="config"
dfdl:lengthKind="implicit">
<xs:complexType>
<xs:sequence dfdl:ref="config">
<xs:element ref="myCount"></xs:element>
<xs:choice dfdl:choiceLengthKind="implicit"
dfdl:ref="config">
<xs:element ref="myInt" minOccurs="1"
maxOccurs="3"></xs:element>
<xs:element ref="myTxt"></xs:element>
</xs:choice>
</xs:sequence>
</xs:complexType>
</xs:element>
Where myInt has occursCountKind="expression" occursCount="{../myCount}"
A given instance of this message could have myCount==0
Is this valid?
Should it resolve to 0 occurrences of myInt or move on to myTxt ?
Section15 of the spec says:
The Root of the Branch MUST NOT be optional. That is XSDL minOccurs MUST
BE greater than 0.
But in this case minOccurs is >0.
Assuming this is not an error then in terms of resolving the choice
section 15.1.1 says..
15.1.1 Resolving Choices via Speculation Speculative resolution works as
follows:
1) Attempt to parse the first branch of the choice.
2) If this fails with a processing error
a) If a dfdl:discriminator evaluated to true earlier on this branch then
the parser is 'bound' to this branch and parsing of the entire choice
construct fails with a processing error.
b) If the branch has a dfdl:initiator and the choice has
dfdl:initiatedContent ‘yes’ then the parser is 'bound' to this branch and
parsing of the entire choice construct fails with a processing error. c)
Otherwise we repeat from step 1 for the next branch of the choice.
3) It is a processing error if the branches of the choice are exhausted.
4) If a branch is successfully parsed without error, then that branch's
infoset becomes the infoset for the parse of the choice construct.
So seems like this is 4.) we did not fail to parse myInt...
However talking with mark about real scenarios that this might apply to, a
choice two repeating fields with counts earlier in the data only one of
which must appear. you'd expect 0 of the first means >0 of the second and
visa versa... So you'd probably want 0 myInt allowed the choice to resolve
to myTxt.
Thoughts ?
If you agree we need more clarity in he spec will forward to WG.
Kind Regards,
- Alex
Alex Wood -
Software Engineer -
WebSphere Message Broker Development
DFDL Development
MP 211, IBM UK Labs, Hursley Park, Winchester, Hants. SO21 2JN.
Tel: Internal 246272, External 01962 816272
Notes: Alex Wood1/UK/IBM at IBMGB
e-mail: wooda at uk.ibm.com
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
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