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@IBMGB e-mail: wooda@uk.ibm.com From: Steve Hanson/UK/IBM To: Alex Wood1/UK/IBM@IBMGB Cc: Andrew Edwards/UK/IBM@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@uk.ibm.com tel:+44-1962-815848 From: Steve Hanson/UK/IBM To: Alex Wood1/UK/IBM@IBMGB Cc: Andrew Edwards/UK/IBM@IBMGB, Mark Frost/UK/IBM@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@uk.ibm.com tel:+44-1962-815848 From: Alex Wood1/UK/IBM To: Steve Hanson/UK/IBM@IBMGB Cc: Andrew Edwards/UK/IBM@IBMGB, Mark Frost/UK/IBM@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@IBMGB e-mail: wooda@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