Open Grid Forum: Data Format Description Language Working Group OGF DFDL Working Group Call, March 31-2010 Attendees Steve Hanson (IBM) Alan Powell (IBM) Steve Marting (Progeny) Stephanie Fetzer (IBM) Mike Beckerle (Oco) Tim Kimber(IBM) Apologies Suman Kalia (IBM) 0 DFDL specification status The draft specification was passed by the OGF technical committee on March 30th so will now be made available for public comment. 1 Nils, defaults and unparsing The semantics need clarifying I have reorganized the table Logical Value initiator region contains content region contains Nil (implies nillable) nilValueInitiatorPolicy 'prohibited' empty representation of nil nilValueInitiatorPolicy 'required' initiator string "" (empty string) (type is xs:string or xs:hexBinary) missingValueInitiatorPolicy 'prohibited' empty empty missingValueInitiatorPolicy 'required' initiator string missing useNilForDefault nilValueInitiatorPolicy 'prohibited' empty representation of nil nilValueInitiatorPolicy 'required' initiator string default is empty string (type is xs:string or xs:hexBinary) missingValueInitiatorPolicy 'prohibited' empty empty missingValueInitiatorPolicy 'required' initiator string Other default initiator string representation of the default value. a non-nil non-empty-string value initiator string representation of the logical value Note: If nilValue is the empty string then missingValueInitiatorPolicy is not used. Other changes: missingValueInitiatorPolicy Enum Valid values ?required', ?prohibited' Specifies whether to expect an initiator when an element is missing. Ignored unless dfdl:initiator is specified and is not "" (empty string). 'required'- Indicates that the dfdl:initiator followed by empty content is the required syntax to indicate that the element is missing. ?prohibited' - Indicates that empty content is the required syntax to indicate that the element is missing. The presence of an initiator implies that real content must follow. Use of ?prohibited' implies an ordered sequence. If used on an initiated element of an unordered group it is a schema definition error. If the element is required, defaulting occurs as defined above. This property also applies on unparsing, when the data to be written (after nil value and default value processing) is empty content. Annotation: dfdl:element (string or hexbinary) The WG agreed that the unparsing table was correct though there was some discussion and misunderstanding about the comment that a nilValue of the empty string did not use missingValueInitiatorPolicy. The comment was asking fro agreement from reviewers and does not add any new rule to the tavle. The meaning of the columns needs a better explanation. SH pointed out that missingValueInitiatorPolicy applies to all simple types not just string and hexbinary and to complex types. The description implies parsing and needs to include unparsing. There was a lot of discussion about paring behaviour. In particular whether there needs to be a differentiation between 'zero length content' and 'missing from the data stream'. Action: Tim will document the parsing use cases so we can verify the parsing table. 2 dfdl:choiceKind 'fixedLength' The main issues are: a) The calculation of the length of the longest branch is not obvious. b) The length units to use - the dfdl:lengthUnits property does not exist on a choice c) The name could be better Proposal is therefore to retain the property but to: i) State the conditions that must apply to use this property, and enforce them in the validator => schema definition error otherwise ii) Decouple the choice from its parent by calculating the length of each branch based solely on the properties of the branches components, irrespective of any parent dfdl:lengthKind The use cases are COBOL redefines. C unions and PL/1 ? Restrictions: - At least one of the choice branches must be of calculable length. (Tim to provide definition of calculable) To be calculable - minOccurs must equal maxOccurs for all children - All lengths will be calculated in bytes. All encodings must be fixed width. Actions: - investigate how PL/1 allocates storage for varchars - investigate how COBOL allocates storage for 'occurs dependingon' and how these are modelled in DFDL. 3 dfdl:occursCountKind 'expression' When dfdl:occursCountKind is 'expression' the occursCount should only be used when parsing. On unpasring the number of occurrences is specified by minOccurs etc Note this behaviour is different from dfdl:lengthKind. Agreed that the dfdl:occursCountKind 'expression' is only used on parsing. 4 Unsigned decimal Whether a logical type is signed or not is used to determine whether a sign is output in some representations. However there isn't an unsigned decimal or integer so these will always be output with a sign so COBOL declarations such as 05 CFCFDN-FLD12 PIC 9(05)V99 COMP-3. cannot be supported. Proposed solution: - Allow xs:nonNegativeInteger which enables unsigned unbounded integers to be modelled. The problem to solve is then just for xs:decimal. - Call the new property dfdl:decimalSigned. It only applies to xs:decimal or user defined restrictions thereof. It applies to all physical decimals, as its name implies (not just zoned or packed). We considered added a dfdl:unsignedDecimal type but rejected it as causing confusion between dfdl type restrictions and user restrictions. The preferred solution is as proposed. Action Mike to agree. 5 dfdl:separatorPoilicy. dfdl:separatorPolicy enumeration definitions are not complete as they do not discuss arrays or defaulting. separatorPolicy="required" All the separators must be there. No group member, except for required members with a default, may be omitted from the data stream. Every group member must have a separator in the correct position. Optional members and variable-occurrence arrays will be allowed, separators will be expected for all maxOccurs ** It is a schema definition error if maxOccurs="unbounded" for any member of the group separatorPolicy="suppressed" Any group member ( optional or required with a default) can be omitted from the data stream, in which case its separator must may also be omitted. For prefix and infix, if a separator is found then another group member is expected. For postfix, if enclosing markup is not found immediately after a postfix separator then another group member is expected. Enclosing markup or end of data can occur where an infix or prefix separator is expected. This terminates the group. Enclosing markup or end of data can occur immediately after a postfix separator (if dfdl:documentfinalSeparatorCanBeMissing is 'yes' then the postfix separator may be missing at the end of the datastream). This terminates the group. If the group terminates before all of its members have been parsed then any required members in the remainder of the group must be defaulted into the infoset. The entire group can have a zero-length representation, which is indicated by enclosing markup at the start of the group's content region. If another group member is expected and the next group member is a point of uncertainty then the identity of the next group member must be determined by resolving the point of uncertainty as described in section XXX. If another group member is expected but no group member is found in the data stream then it is a processing error. If another group member is expected but all group members have been parsed then it is a processing error. separatorPolicy="suppressedAtEnd" suppressAtEnd has the same rules as 'required' up to the last required member that does not have a default, then it has the same rules as 'suppressed' Open questions 1. If a group has separatorPolicy='required' and one of its optional members has a zero-length representation, and that member is allowed to have a zero-length representation, what should the parser do? A similar question arises for required, defaultable elements with a zero-length representation when they are based on a type with xs:minLength="0". Should the default value be used, or the empty string? 2. How should the occursXXX properties be applied when there are other ways to determine the number of occurences ( e.g. by counting separators )? 3. What algorithm should the parser use to decide whether to default a complex element or group ( when the element/group is a child of a separated group)? 4. How does unparsing work for separated groups in all of these scenarios? The changes above were suggested. The unparsing behaviour needs adding. There was discussion about defaulting of complex elements and when this should occur. More discussion is needed. 6 Current Actions Updated below Meeting closed, 15:00 Next call Wednesday 7 April January 2010 13:00 UK (8:00 ET) Next action: 091 Actions raised at this meeting No Action 088 define semantics of choiceKind 'fixedLength' 31/03: TK to provide definition of calculable length. Investigate PL/I varchars and Cobol occurs dependingon. 089 Need to be able to define unsigned decimal and integer 31/03: MB to agree proposed solution 090 Semantics of separatorPolicy Current Actions: No Action 066 Investigate format for defining test cases 25/11:IBM to see if it is possible to publish its test case format. 04/12: no update 09/12: no update 16/12: reminded dent to project manager 23/12: SH will send another reminder. 06/01: Another reminder will be sent 13/01: no update 20/01: no update 27/01: no progress 29/01: no progress 03/02: IBM is still investigating 10/02: IBM is still investigating 17/02: IBM is willing in principle to publish the test case format and some of the test cases. May need some time to build a 'compliance suite' 24/03: No progress 03/03: Discussions have been taking place on the subset of tests that will be provided. 10/03: work is progressing 17/03: work is progressing 31/03: work is progressing 084 Check behaviour of dfdl:inputValueCalc and outputValueCalc. 085 ALL: publicize Public comments phase to ensure a good review.. 086 AP: Nils and Defaults during unparsing - update table 31/03: TK to documetn use cases for parsing 088 define semantics of choiceKind 'fixedLength' 31/03: TK to provide definition of calculable length. Investigate PL/I varchars and Cobol occurs dependingon. 089 Need to be able to define unsigned decimal and integer 31/03: MB to agree proposed solution 090 Semantics of separatorPolicy Closed actions No Action Work items: No Item target version status 005 Improvements on property descriptions not started 012 Reordering the properties discussion: move representation earlier, improve flow of topics not started 036 Update dfdl schema with change properties ongoing 042 Mapping of the DFDL infoset to XDM none not required for V1 specification 070 Write DFDL primer 071 Write test cases. 083 Implement RFC2116 097 Remove functions that returns duration 098 occursCountKind is parsing only Regards Alan Powell Development - MQSeries, Message Broker, ESB IBM Software Group, Application and Integration Middleware Software ------------------------------------------------------------------------------------------------------------------------------------------- IBM MP211, Hursley Park Hursley, SO21 2JN United Kingdom Phone: +44-1962-815073 e-mail: alan_powell@uk.ibm.com Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. 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