Hi Geoff, I'll certainly put this on the agenda. If anyone has anything else please let me know. Also some comments: 1. I'd like to understand how variables relate to parameters, specifically: a. Could we actually define variables to be user-defined parameters? (if not, why not?) b. If (a) doesn't work can we have variables use the same scoping rules as parameters? 2. In the extensibility group we have been talking about reference direction. It was proposed that XPaths in a DFDL document can only refer to elements higher up the document (i.e. backwards only) they cannot reference things below them (which will not yet have been parsed). With the use of "hidden layers" this can be done without loss of generality. I would suggest that variable references should work this way. I.e you are only allowed to refer to data that has already been parsed. Thanks, Martin _____ From: Geoff Judd [mailto:JUDDG@uk.ibm.com] Sent: Tuesday, December 13, 2005 9:34 AM To: Westhead, Martin (Martin) Cc: dfdl-wg@ggf.org Subject: Re: [dfdl-wg] Telcon Notes Martin, Please can you add a discussion of the semantics of DFDL Variables to the agenda of tomorrow's telecon. I have attached a document with some thoughts that I have had on the subject. Regards, Geoff Judd Websphere MQ Integrator Development IBM UK Ltd Hursley Telephone: +44-1962-818461 E-mail: JUDDG@uk.ibm.com "Westhead, Martin (Martin)" <westhead@avaya.com> Sent by: owner-dfdl-wg@ggf.org 30/11/2005 18:12 To <dfdl-wg@ggf.org> cc Subject [dfdl-wg] Telcon Notes Present ------- Mike Bekerle Tara Talbott Martin Westhead Geoff Judd Steve Hanson Bob McGrath Reports from Active Trackers ---------------------------- Scoping tracker is being worked on - no news. Extensibility group is moving forward - nothing to report yet Discussion of Geoff's documents ------------------------------- Variables doc Mike observed that variables could be used in place of his extensibility proposal on annotations. Martin asked about whether we wanted to include this in the standard. Is the complexity worth the addition - the feeling of the meeting was probably it was. Martin proposed that instead of binding a variable value to an element, the variable value should be set with an XPath expression. Discussed the question as to whether the variable value can be reset, whether it can/should be scoped in the same way as annotation attributes. Next step will be for Geoff to revise the document to look at cases where value may need to be reset and start to explore some of the semantic issues involved. Choices doc Discriminator type - what if discriminator is not a string? For efficiency can we handle discriminators that are integers? Suggest that instead of discriminators being computed to strings they are computed to an XPath value with its implied type so that numeric discriminators do need to be converted to strings. Wildcard docs Group seemed fairly happy with this proposal as it stands.
Martin, Please see my comments below. Regards, Geoff Judd Websphere MQ Integrator Development IBM UK Ltd Hursley Telephone: +44-1962-818461 E-mail: JUDDG@uk.ibm.com "Westhead, Martin \(Martin\)" <westhead@avaya.com> 13/12/2005 17:57 To Geoff Judd/UK/IBM@IBMGB cc <dfdl-wg@ggf.org> Subject RE: [dfdl-wg] Telcon Notes Hi Geoff, I?ll certainly put this on the agenda. If anyone has anything else please let me know. Also some comments: 1. I?d like to understand how variables relate to parameters, specifically: a. Could we actually define variables to be user-defined parameters? (if not, why not?) b. If (a) doesn?t work can we have variables use the same scoping rules as parameters? GJ: This is a good point which I have omitted from the semantics document. However I had considered this when looking at late binding of schemas and runtime schemas. I think variables in DFDL should be similar to XSLT parameters. That is the value of a variable can be set externally although the mechanism for this will not be specified. If a value of a variable is set externally it is the equivalent of binding a value to the variable so it cannot have another value bound to it. Also I think that for a valoue to be set externally the declaration of the variable should be made at the schema level. 2. In the extensibility group we have been talking about reference direction. It was proposed that XPaths in a DFDL document can only refer to elements higher up the document (i.e. backwards only) they cannot reference things below them (which will not yet have been parsed). With the use of ?hidden layers? this can be done without loss of generality. I would suggest that variable references should work this way. I.e you are only allowed to refer to data that has already been parsed. GJ: I agree that only variables that have been declared and have either a default value or a value bound to them can be referenced. If this is not the case it will result in a runtime error. Does this answer your question or have I mis-understood what you mean ? Thanks, Martin From: Geoff Judd [mailto:JUDDG@uk.ibm.com] Sent: Tuesday, December 13, 2005 9:34 AM To: Westhead, Martin (Martin) Cc: dfdl-wg@ggf.org Subject: Re: [dfdl-wg] Telcon Notes Martin, Please can you add a discussion of the semantics of DFDL Variables to the agenda of tomorrow's telecon. I have attached a document with some thoughts that I have had on the subject. Regards, Geoff Judd Websphere MQ Integrator Development IBM UK Ltd Hursley Telephone: +44-1962-818461 E-mail: JUDDG@uk.ibm.com "Westhead, Martin (Martin)" <westhead@avaya.com> Sent by: owner-dfdl-wg@ggf.org 30/11/2005 18:12 To <dfdl-wg@ggf.org> cc Subject [dfdl-wg] Telcon Notes Present ------- Mike Bekerle Tara Talbott Martin Westhead Geoff Judd Steve Hanson Bob McGrath Reports from Active Trackers ---------------------------- Scoping tracker is being worked on - no news. Extensibility group is moving forward - nothing to report yet Discussion of Geoff's documents ------------------------------- Variables doc Mike observed that variables could be used in place of his extensibility proposal on annotations. Martin asked about whether we wanted to include this in the standard. Is the complexity worth the addition - the feeling of the meeting was probably it was. Martin proposed that instead of binding a variable value to an element, the variable value should be set with an XPath expression. Discussed the question as to whether the variable value can be reset, whether it can/should be scoped in the same way as annotation attributes. Next step will be for Geoff to revise the document to look at cases where value may need to be reset and start to explore some of the semantic issues involved. Choices doc Discriminator type - what if discriminator is not a string? For efficiency can we handle discriminators that are integers? Suggest that instead of discriminators being computed to strings they are computed to an XPath value with its implied type so that numeric discriminators do need to be converted to strings. Wildcard docs Group seemed fairly happy with this proposal as it stands.
participants (2)
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Geoff Judd -
Westhead, Martin (Martin)