Allowing dfdl:lengthKind on choices has other benefits. It means that elements, sequences and choices are consistent in how they are capable of being extracted (literal length, XPath, model determined, prefixed, null terminated). I don't think unresolvableWhenParsing implies fixed length storage. I could have an unresolvable choice being two variable length strings, terminated by the terminator of the choice. Regards, Steve Steve Hanson WebSphere Message Brokers Hursley, UK Internet: smh@uk.ibm.com Phone (+44)/(0) 1962-815848 Mike Beckerle/Worcester/IBM@IBMUS 20/11/2007 21:23 To Steve Hanson/UK/IBM@IBMGB cc dfdl-wg@ogf.org Subject Re: [DFDL-WG] Grammar as adapted to infoset Rather than overloading "implicit" length to mean this, I think we need an enum-valued property for choices. Today there is this choiceUnresolvableWhenParsing boolean. I think this shoudl become choiceType="unresolvableWhenParsing". Then we can have an enum value for the case where all arms of the choice are assumed to be padded to max length of the alternative. So I think we have 3 enum values: variableLength fixedLength unresolvableWhenParsing variableLength means the storage taken depends on the alternative selected, Fixed length means shorter alternatives are padded to the length of the longest. unresolvable means what it means now, which is that you can't tell which variant it is (which also implies the storage required is fixed length). ...mikeb Mike Beckerle STSM, Architect, Scalable Computing IBM Software Group Information Platform and Solutions Westborough, MA 01581 direct: voice and FAX 508-599-7148 assistant: Pam Riordan priordan@us.ibm.com 508-599-7046 Steve Hanson/UK/IBM@IBMGB 11/19/2007 07:13 AM To Mike Beckerle/Worcester/IBM@IBMUS cc dfdl-wg@ogf.org Subject Re: [DFDL-WG] Grammar as adapted to infoset Or allow xs:choice to carry dfdl:length & dfdl:lengthKind. Then lengthKind="implicit" could mean the length is the longest of the modelled alternatives. Regards, Steve Steve Hanson WebSphere Message Brokers Hursley, UK Internet: smh@uk.ibm.com Phone (+44)/(0) 1962-815848 Mike Beckerle/Worcester/IBM@IBMUS 16/11/2007 19:29 To Steve Hanson/UK/IBM@IBMGB cc dfdl-wg@ogf.org Subject Re: [DFDL-WG] Grammar as adapted to infoset There are of course alternatives. E.g., a hidden or non-hidden field which is a byte array or hexBinary to absorb the padding bytes at the ends of the shorter variants. Or one could put trailing skip bytes on the last element or group of each of the shorter variants. One can also encapsulate the whole choice in a sequence whose length is the fixed maximum length. This is my personal favorite, since it uses the FinalUnused that is already in the grammar. E.g., suppose the length of the longest variant is 258 bytes. <sequence dfdl:lengthKind="explicit" dfdl:length="258" dfdl:lengthUnits="bytes" dfdl:applies="hereOnly"> <choice> ..... </choice> </sequence> The only thing I don't like about this is I don't have a way to express the length other than to hard-code the constant 258, but since tooling would typically put this in based on Cobol descriptors or other information I don't mind so much. ...mikeb Mike Beckerle STSM, Architect, Scalable Computing IBM Software Group Information Platform and Solutions Westborough, MA 01581 direct: voice and FAX 508-599-7148 assistant: Pam Riordan priordan@us.ibm.com 508-599-7046 Steve Hanson/UK/IBM@IBMGB 11/16/2007 11:24 AM To Mike Beckerle/Worcester/IBM cc dfdl-wg@ogf.org Subject Re: [DFDL-WG] Grammar as adapted to infoset Hi Mike One extra thought post-call, caused by thinking about the FinalUnused part of a sequence. Some fixed length choices have a rule that each branch of the choice must be of equal length. This results in unused bytes for branches shorter than the maximum. In a bitstream instance, a user will see these bytes. Perhaps the grammar should acknowledge their existence, even if there are no DFDL properties to express the bytes (like FinalUnused)? Regards, Steve Steve Hanson WebSphere Message Brokers Hursley, UK Internet: smh@uk.ibm.com Phone (+44)/(0) 1962-815848 Mike Beckerle <beckerle@us.ibm.com> Sent by: dfdl-wg-bounces@ogf.org 10/11/2007 00:16 To dfdl-wg@ogf.org cc Subject [DFDL-WG] Grammar as adapted to infoset I took a crack at this. I ripped it out of the main document for faster review/turnaround. I think this matches the latest infoset email diagram. Mike Beckerle STSM, Architect, Scalable Computing IBM Software Group Information Platform and Solutions Westborough, MA 01581 direct: voice and FAX 508-599-7148 assistant: Pam Riordan priordan@us.ibm.com 508-599-7046 -- dfdl-wg mailing list dfdl-wg@ogf.org http://www.ogf.org/mailman/listinfo/dfdl-wg 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