Hi Suman, The DFDL expression language does not permit forward references when parsing. See Alan's document which has been rolled into draft 031. You'll have to push the discriminator down inside the group. Regards, Steve Steve Hanson WebSphere Message Brokers Hursley, UK Internet: smh@uk.ibm.com Phone (+44)/(0) 1962-815848 Suman Kalia <kalia@ca.ibm.com> Sent by: dfdl-wg-bounces@ogf.org 14/02/2008 20:04 To dfdl-wg@ogf.org cc Subject [DFDL-WG] Fw: DFDL: Minutes from OGF WG call, 13 Feb 2008 I have reworked the example where the choice branch condition was specified outside the choice contents. We don't have to specifically mention switch, case statement programming paradigm in DFDL; thinking more about this, I believe switch/case statement paradigm is not relevant here. Attached is the reworked example . I also created another example by importing COBOL copy book (containing redefine clause) using IBM message broker toolkit. Here the branch condition is described inside the choice . In this case the discriminator contain forward reference to check the condition value; implementations may want to restrict the forward reference to the first token within the contents of choice branch. Note : Discriminators are useful when user is dealing with binary or text data which is not tagged.. Your comments/ suggestions are most welcome and appreciated.. Suman Kalia IBM Toronto Lab WebSphere Business Integration Application Connectivity Tools Tel : 905-413-3923 T/L 969-3923 Fax : 905-413-4850 T/L 969-4850 Internet ID : kalia@ca.ibm.com ----- Forwarded by Suman Kalia/Toronto/IBM on 02/14/2008 02:47 PM ----- Ian W Parkinson <PARKIW@uk.ibm.com> Sent by: dfdl-wg-bounces@ogf.org 02/14/2008 01:34 PM To dfdl-wg@ogf.org cc Subject [DFDL-WG] DFDL: Minutes from OGF WG call, 13 Feb 2008 Open Grid Forum: Data Format Description Language Working Group Weekly Working Group Conference Call 17:00 GMT, 13 Feb 2008 Attendees Mike Beckerle (Oco) Steve Hanson (IBM) Suman Kalia (IBM) Simon Parker (PolarLake) Ian Parkinson (IBM) Apologies Alan Powell (IBM) 1. Specification Draft Status Alan has distributed draft 31 of the DFDL specification. The meeting reviewed the plan for the next few versions of the drafts and updated it to reflect progress and revised target dates - a copy of the updated plan is attached to these minutes. Simon's UML diagrams describing the schema components are now planned for inclusion in draft 32 but require further discussion. This discussion will be added to the agenda for the DFDL-WG call on 27th February, but Simon would appreciate comments via e-mail before then. These diagrams are intended to set a conceptual model for DFDL and to show where annotations may be attached, but will not be used more formally, e.g. to automatiically generate APIs. The work on nulls/defaults/optionals is complete, except for some small details, which will be included in draft 32. The 'valueCalc' work has been progressed but is not complete, and is also now targeted for draft 32. Other items originally planned for draft 31 are complete and have been included in the draft. 2. Assertions, Discriminators and Choice Suman has distributed an example showing the use of discriminators in choice constructs in DFDL schemas. The meeting discussed the distinction between discriminators and assertions - Mike described an assertion as simply a predicate which, if encountered within a choice, can cause backtracking. In contrast a succesful discriminator expression would lock the choice into a particular branch. If no discriminator matches, then the parse would fail - unless, as Simon pointed out, the choice itself was optional. Simon also suggested that the last branch of a choice could be left without a discriminator to act a a catch-all, but felt that the purpose of a discriminator should be more to help disambiguate between the possible branches rather than form such a "swtich" construct. Steve asked about the timing attribute on assertions, and in particular whether we'd need a similar attribute for discriminators. Mike suggested that the timing attribute might have been included simply to make implementation easier; as without it an implementation would need to perform a significant amount of static analysis. The motivation for discriminators was to allow a choice to be resolved by data encountered before the choice. However as Steve and Suman thought there were use cases where a discriminator might need to refer to elements inside the choice, and so a timing option would be useful. Suman will prepare such an example, and Mike will schedule a further discussion of this topic. Simon distributed an alternative example, showing the use of fixed fields instead of discriminators or assertions., which he felt might form a useful starting point for a full description of choice disambiguation. (Steve left the meeting) 3. Presentation for next OGF conference Simon suggested that Mike highlight the recent discussion topics of the working group, and items which have recently been added to the specification, and asked whether it would be useful to include the UML diagrams. Mike would like to display the diagrams and see whether they trigger a discussion amongst the delegates. He would also like to present work on variable markup and valueCalc. Meeting closed, 18:00 GMT Attachment: revised plan for specification drafts Draft 31: Improve (finish?) nulls/defaults/optionals (Mike, with input from Steve) - Done, apart from minor edit task Expression language (Alan) - Done Property precedence for parsing (Steve) - Done Entities, including basic white space (Alan) - Done Draft 32 ("vX+2"): valueCalc (Mike) - Feb 27, 2008 Remaining aspects of null/default/optionals (Alan) - Mar 5, 2008 2-level description of schema components, including UML (Simon) - Feb 27, 2008 Property precedence for writing (Steve) - Feb 15, 2008 Variable markup (Steve) - Feb 29, 2008 Regular expressions for lengths (Alan) Bring supplements up-to-date (Steve) - Mar 7, 2008 Assertions, discriminators and choice, including discussion of timing option (Suman) - Feb 19, 2008 How speculative parsing works (combining choice and variable-occurence - currently these are separate) (TX person) Reordering the properties discussion: move representation earlier, improve flow of topics (Alan) Draft 33: ("vX+3"): Escape schemes (Ian P) - Mar 21, 2008 String XML type (Ian P) - Mar 21, 2008 Variables (Mike) Selectors (Suman) - Mar 3, 2008 Improvements on property descriptions (All - split TBD) Envelopes and Payloads (Steve) - Mar 5, 2008 Extraneous to spec: Develop Schema for DFDL xsd (Suman) - Mar 15, 2008 Develop Schema for Schema DFDL Subset xsd (Suman) - Mar 30, 2008 (might not be needed) Ian Parkinson WebSphere ESB Development Mail Point 211, Hursley Park, Hursley, Winchester, SO21 2JN, UK 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 -- dfdl-wg mailing list dfdl-wg@ogf.org http://www.ogf.org/mailman/listinfo/dfdl-wg-- 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