- dfdl-wg - lists.ogf.org

Action 277: when is the separator expression evaluated?
by Steve Hanson 29 Jan '15

29 Jan '15

Mike to run the below past the Daffodil team. Regards Steve Hanson Architect, IBM DFDL Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848 ----- Forwarded by Steve Hanson/UK/IBM on 19/01/2015 17:58 ----- From: Steve Hanson/UK/IBM To: Tim Kimber/UK/IBM@IBMGB Cc: DFDL-WG <dfdl-wg(a)ogf.org> Date: 19/12/2014 11:51 Subject: Re: [DFDL-WG] when is the separator expression evaluated? Section 16.3 of the spec says: 16.3 Arrays with DFDL Expressions If the value of a DFDL property of an array element (other than dfdl:occursCount) is given by a DFDL Expression, then the expression must be re-evaluated for each occurrence of the element in case the value changes. Relating this to Mike's original question, I would say that the separator for the sequence within 'data' is re-evaluated for each occurrence of 'data', but it is not re-evaluated for each occurrence of 'num'. The order in which properties are referenced is given by section 22 of the spec. (I am sure this does not cover every nuance, but let's assume it does). It should not make a difference if a property is fixed or an expression; so when a property is referenced the expression is evaluated. I am happy for implementations to defer the evaluation of the expression BUT only as long as deferral does not change the result that would have been obtained if the expression had been evaluated at the original time of reference. Regards Steve Hanson Architect, IBM DFDL Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848 From: Tim Kimber/UK/IBM@IBMGB To: DFDL-WG <dfdl-wg(a)ogf.org> Date: 18/12/2014 16:24 Subject: Re: [DFDL-WG] when is the separator expression evaluated? Sent by: dfdl-wg-bounces(a)ogf.org Good questions. I think the questions apply equally to separator and terminator, which can both be defined on the sequence group. Parsing: The first member may have lengthKind='explicit' and will therefore not need the separator until the parsing of the first member is complete. The terminator will be required as soon as the parser has to look for delimiters in the 'trailing optional' area of the sequence group. So we need to decide whether a) DFDL expressions for separators/terminators are evaluated upon entering the sequence group or b) DFDL expressions for separators/terminators can be evaluated lazily or c) DFDL expressions for separators/terminators must be evaluated lazily Serializing: The separator will be required after the first member, regardless. The terminator may be required before the end of the group if one or more group members have an escape scheme. I'm inclined to suggest that implementations should be free to evaluate eagerly or lazily, as long as the behaviour conforms to the DFDL spec. But there may be scope for conforming implementations to exhibit material differences in behaviour if we allow that much latitude. I just can't think what those differences would be. regards, Tim Kimber, Technical Lead for IBM Integration Bus Healthcare Pack Hursley, UK Internet: kimbert(a)uk.ibm.com Tel. 01962-816742 Internal tel. 37246742 From: Mike Beckerle <mbeckerle.dfdl(a)gmail.com> To: Tim Kimber/UK/IBM@IBMGB Cc: "dfdl-wg(a)ogf.org" <dfdl-wg(a)ogf.org> Date: 17/12/2014 18:19 Subject: Re: [DFDL-WG] when is the separator expression evaluated? Great. I concur. Anybody have the opposite perspective? Where should a clarification go? In general, suppose <xs:sequence dfdl:terminator="....some expression..."> .... does the expression get evaluated when the xs:sequence is first "entered" by the parser (whatever "entered" means - when the parser conceptually walks into this construct of the schema), or as late as possible - when the terminator is actually needed for something. Consider - parsing we may need the terminator quite soon, as the terminator may play a role in delimiting the very first thing one finds inside the sequence. When unparsing, if you happen to know there are 5 things in the sequence from the Infoset, you don't really need the terminator at all until after you have unparsed the 5th thing, i.e., much later. This asymetry is of concern. Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com Please note: Contributions to the DFDL Workgroup's email discussions are subject to the OGF Intellectual Property Policy On Wed, Dec 17, 2014 at 10:28 AM, Tim Kimber <KIMBERT(a)uk.ibm.com> wrote: A separator as something that applies to the entire group, so I'm uncomfortable with the idea of (potentially ) changing it for every member of the group. So I would vote for: 1) The separator is evaluated once per 'data' element; occursIndex evaluates to index in the 'data' array; If 2) was desired it could be achieved by setting the terminator on num: <element name="e2"> <sequence separator="|" separatorPosition="infix"> <element name="seps" minOccurs="3" maxOccurs="3"/> <element name="data" maxOccurs='10'> <sequence> <element name="num" maxOccurs='10' terminator="{ /e2/seps[dfdl:occursIndex()] }" /> </sequence> </element> </sequence> </element> ..and the infix-ness could be emulated by setting the terminator to "" when dfdl:occursIndex() eq count( /e2/seps). regards, Tim Kimber, Technical Lead for IBM Integration Bus Healthcare Pack Hursley, UK Internet: kimbert(a)uk.ibm.com Tel. 01962-816742 Internal tel. 37246742 From: Mike Beckerle <mbeckerle.dfdl(a)gmail.com> To: "dfdl-wg(a)ogf.org" <dfdl-wg(a)ogf.org> Cc: Norm Patrick <npatrick(a)tresys.com>, Jessie Chab < jchab(a)tresys.com> Date: 16/12/2014 22:40 Subject: [DFDL-WG] when is the separator expression evaluated? Sent by: dfdl-wg-bounces(a)ogf.org Jessie Chab came up with this interesting case. I am hoping someone else remembers somewhere in the spec where this order of evaluation issue is taken up in detail. Consider: <element name="e2"> <sequence separator="|" separatorPosition="infix"> <element name="seps" minOccurs="3" maxOccurs="3"/> <element name="data" maxOccurs='10'> <sequence separator="{ /e2/seps[dfdl:occursIndex()] }"> <element name="num" maxOccurs='10' /> </sequence> </element> </sequence> </element> So we first parse 3 strings separated by a pipe. After that's parsed, lets assume our infoset looks like this: <e2> <seps>;</seps> <seps>-</seps> <seps>#</seps> </e2> After that we will have some 'data' elements (separated by pipes) which each have a sequence of 'num' elements. The question is what are the valid separators of the 'num' elements. I see two potential interpretations. 1) The separator is evaluated once per 'data' element; occursIndex evaluates to index in the 'data' array; valid data might look something like: ;|-|#|a;b;c;d|e-f-g-h|i#j#k#l Note that this means the size of the data array must be less than or equal to the size of the seps array (though that could be worked around using mod 3 arithmetic.) 2) Everytime we need to look for a separator between a num element, we reevaluate the separator expression. This means the occursIndex() references the index in the 'num' array, and so valid data might look something like: ;|-|#|a;b-c#d|e;f-g#h|i;j-k#l Note that this means the size of the num array must be less than or equal to the size of the seps array. I recall we were considering an argument to dfdl:occursIndex() to make exactly this kind of issue clear. I believe we decided against it, as we weren't able to pin down the semantics quite clearly. E.g., in the above, how would you add an argument to the dfdl:occursIndex(...) call that points to the num array, which isn't even in scope at that point? I know we say somewhere in the spec that separator can be defined, in say, the default format of some other schema file. It can be an expression, and that expression isn't evaluated until some sequence which has that separator in scope. Which means the expression can refer to path steps and such that are meaningless at the point where it appears lexically, but will be meaningful for a sequence where that separator expression is in scope. But this problem is slightly different. The question is whether the evaluation is per-item of the sequence, or once for the sequence. ...mikeb Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com Please note: Contributions to the DFDL Workgroup's email discussions are subject to the OGF Intellectual Property Policy -- dfdl-wg mailing list dfdl-wg(a)ogf.org https://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 -- dfdl-wg mailing list dfdl-wg(a)ogf.org https://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 -- dfdl-wg mailing list dfdl-wg(a)ogf.org https://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 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

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OGF DFDL WG Call Minutes 2015-01-27
by Steve Hanson 27 Jan '15

27 Jan '15

Please find minutes from the above call at https://redmine.ogf.org/dmsf_files/13385?download= Regards Steve Hanson Architect, IBM DFDL, Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848

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OGF DFDL WG Call Agenda 2015-01-27
by Steve Hanson 26 Jan '15

26 Jan '15

Please find agenda for call on Redmine at https://redmine.ogf.org/dmsf_files/13385?download= (ignore that it says 20th) Regards Steve Hanson Architect, IBM Data Format Description Language (DFDL) Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848

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OGF DFDL WG Call 2015-01-20 - cancelled
by Steve Hanson 20 Jan '15

20 Jan '15

Today's call is cancelled as not enough people available. Next meeting is 27th. Regards Steve Hanson Architect, IBM DFDL Co-Chair, OGF DFDL Working Group Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848

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Cancelled: DFDL Working Group Call
by Steve Hanson 20 Jan '15

20 Jan '15

Mike not available so call cancelled

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OGF DFDL WG Call Agenda 2015-01-20
by Steve Hanson 19 Jan '15

19 Jan '15

Please find agenda for call on Redmine at https://redmine.ogf.org/dmsf_files/13385?download= Regards Steve Hanson Architect, IBM Data Format Description Language (DFDL) Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848

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OGF DFDL WG Call Minutes 2015-01-13
by Steve Hanson 13 Jan '15

13 Jan '15

Please find minutes from the above call at https://redmine.ogf.org/dmsf_files/13383?download= Regards Steve Hanson Architect, IBM DFDL, Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848

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OGF DFDL WG Call Agenda 2015-01-13
by Steve Hanson 13 Jan '15

13 Jan '15

Please find agenda for call on Redmine at https://redmine.ogf.org/dmsf_files/13383?download= Regards Steve Hanson Architect, IBM Data Format Description Language (DFDL) Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848

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DFDL Experience 4 - Errata for GFD.207
by Steve Hanson 13 Jan '15

13 Jan '15

I have added a working document to https://redmine.ogf.org/dmsf/dfdl-wg?folder_id=5485. It is the 4th DFDL experience document and provides a consolidated list of errata against GFD.207. It is derived from the issue trackers on Redmine at https://redmine.ogf.org/projects/dfdl-wg/issues. Regards Steve Hanson Architect, IBM DFDL Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848 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

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Fw: Erratum 2.100 (was Action 183 - chicken-and-egg situation with lengths given by expressions)
by Steve Hanson 12 Jan '15

12 Jan '15

After internal discussion, IBM proposes the following: No new dfdl:lengthKind enums dfdl:lengthKind 'explicit' is always considered to be 'fixed length' When dfdl:length is an expression, it is always evaluated when unparsing If the intent is for the infoset data of the element to provide the length, the integer element that is the target of the expression should use dfdl:outputValueCalc with function dfdl:valueLength() referring forward to the infoset element. (Use of dfdl:contentLength() is a schema definition error as it can cause deadlock). It should be noted that dfdl:valueLength() returns an unpadded length. This does not take into account the XSD minLength or dfdl:textOutputMinLength properties. The net is that for simple text elements with dfdl:textPadKind 'padChar', 'delimited', 'pattern', 'prefixed' are considered variable length when unparsing and are padded to a minimum length, and 'implicit', 'explicit', 'endOfParent' have a target length and are padded to that length. Similar for xs:hexBinary elements, 'delimited', 'pattern', 'prefixed' are always padded to a minimum length, and 'implicit', 'explicit', 'endOfParent' are always padded to target length. So for a text element with dfdl:textPadKind 'padChar', or a xs:hexBinary element, and its unpaddedLength is less than the minimum, 'explicit' (expression) is not identical in behaviour to 'prefixed'. If the last point is thought to be a problem, options are to allow dfdl:valueLength() to return minimum length or actual length depending on a new argument, or create a new function to return minimum length. This can be done under existing deferred action 242. To verify that these changes fit into the spec ok, I have updated it - change tracking on and comment for each change. Regards Steve Hanson Architect, IBM DFDL Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848 ----- Forwarded by Steve Hanson/UK/IBM on 12/01/2015 10:20 ----- From: Steve Hanson/UK/IBM To: Tim Kimber/UK/IBM@IBMGB Cc: "Mike Beckerle" <mbeckerle.dfdl(a)gmail.com>, DFDL-WG <dfdl-wg(a)ogf.org> Date: 06/01/2015 15:54 Subject: Re: [DFDL-WG] Erratum 2.100 (was Action 183 - chicken-and-egg situation with lengths given by expressions) A thought. We could add dfdl:lengthKind 'expression', use dfdl:length for the expression, and add a new enum property that is the policy for the expression - that is, evaluate on parse only, or evaluate on both parse and unparse. The enum for the latter is the equivalent of the pre-erratum 2.100 'explicit' and expression behaviour as implemented by IBM DFDL today - which we would then deprecate in the spec (or even remove) and deprecate in IBM DFDL. Regards Steve Hanson Architect, IBM DFDL Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848 From: Steve Hanson/UK/IBM To: Tim Kimber/UK/IBM@IBMGB, "Mike Beckerle" <mbeckerle.dfdl(a)gmail.com> Cc: DFDL-WG <dfdl-wg(a)ogf.org> Date: 10/12/2014 09:08 Subject: Re: [DFDL-WG] Erratum 2.100 (was Action 183 - chicken-and-egg situation with lengths given by expressions) Tim & Mike - replies in-line. Concensus is heading towards 'explicit' working as per IBM DFDL today, so we need to decide on the best way to express the 2.100 behaviour. Regards Steve Hanson Architect, IBM DFDL Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848 From: Tim Kimber/UK/IBM@IBMGB To: dfdl-wg(a)ogf.org Date: 09/12/2014 23:25 Subject: Re: [DFDL-WG] Erratum 2.100 (was Action 183 - chicken-and-egg situation with lengths given by expressions) Sent by: dfdl-wg-bounces(a)ogf.org My 2 cents: lengthKind 'explicit' should continue to work as it currently does in the IBM implementation. That is, it should use the static or calculated value of the length, and pad to that length when unparsing. Otherwise we have different rules for lengthKind='explicit' depending on whether it is an expression or a static value. If somebody wants to avoid padding, then they can put an outputValueCalc on the length field and calculate a value that requires no padding. I think the required expression would be {dfdl:valueLength(../variableLengthField)} With these rules there is a potential for a mutual dependency ( deadlock ) when outputValueCalc is used with a calculated length. If the outputValueCalc is {dfdl:contentLength(../variableLengthField)} then the entire representation length ( including the padding characters ) is being requested. This obviously cannot be satisfied until the padding has been applied, but the padding cannot be applied until the length is known...etc. I don't think this should affect the decision about lengthKind though, for two reasons: - it's already possible to create deadlocks using other calculated fields in DFDL. Any robust implementation of a serializer must include deadlock detection in the evaluation of DFDL expressions. - it would not be difficult to detect the simple case statically and report a schema definition error. SMH: Corrected function names to match spec. The only downside of this is that users who want to calculate the output length for themselves have to jump through the non-obvious hoop of adding outputValueCalc to the length field and selecting the correct (non-deadlocking) DFDL function. But for fields have representation='text' and lengthUnits='characters' there is a simpler alternative: set the length expression to {fn:length(.)}. Other cases will be derivable from the infoset value by a simple calculation, so the outputValueCalc solution should only be required for the hard cases. SMH: Your fn:length(.) does not work unfortunately. The expression does not give the desired length when parsing. regards, Tim Kimber From: Mike Beckerle <mbeckerle.dfdl(a)gmail.com> To: Steve Hanson/UK/IBM@IBMGB Cc: DFDL-WG <dfdl-wg(a)ogf.org> Date: 09/12/2014 18:06 Subject: Re: [DFDL-WG] Erratum 2.100 (was Action 183 - chicken-and-egg situation with lengths given by expressions) Sent by: dfdl-wg-bounces(a)ogf.org Idea 1: Just provide an infoset member [contentLength] which would allow one to get and (when unparsing) set the content length. This would provide the "sticky" content length memory that people are seeking when they say they want data to round-trip. If the same infoset object is parsed and then unparsed, the existence of this [contentLength] member provides the memory of the content length from the parse. An outputValueCalc could meaningfully ask for dfdl:contentLength() which would return the value of this member. If unset, then when unparsing the value of this member can be defined to be the dfdl:valueLength() of the infoset value. SMH; Not keen on this. It makes the DFDL infoset deviate too much from the XML infoset. Idea 2: Per our discussion on the call, I think we are trying to get two behaviors into the same length kind, and we can't have it both ways. So I am fine if we say lengthKind 'explicit' evaluates the expression both parsing and unparsing. I would suggest new lengthKind 'explicitParseOnly' evaluates the expression only when parsing. When this is used, an outputValueCalc would be needed to compute the length value and unparse the representation of it. That calculation would likely need to refer to the dfdl:valueLength() of the element whose length needs to be stored. SMH: Not keen on the name. Let's keep thinking! Idea 3: An alternative would be to introduce property dfdl:unparseContentLength which is an integer constant, or an expression, or one of three special enum values. When dfdl:unparseContentLength='useLength' then it would be the same value as the length (same constant, or computed by evaluating the same expression). Or if dfdl:unparseContentLength='useValueLength' would mean that the length is equivalent to writing dfdl:unparseContentLength='{ dfdl:valueLength(., LU) }', where LU is the length units of the element that is the first argument). Nothing would be automatically saving out the explicitly computed length, so an outputValueCalc would need to be able to get at the dfdl:valueLength or dfdl:contentLength - which would return the value of the dfdl:unparseContentLength) A thought: perhaps we really only need the enum values, and not the ability to specify constants or expressions? In that case I'd suggest the property have the "policy" suffix on the name, i.e., dfdl:unparseContentLengthPolicy. Other possible name choices for this property: dfdl:explicitLengthKindUnparsePolicy or dfdl:lengthKindExplicitUnparsePolicy. I guess we get our choice of whether we add new length kinds along with 'explicit' and we define lengthKind 'explicit' to be one of these behaviors, or we add this enum policy property to add additional meaning when the lengthKind is 'explicit'. The difference of the two is taste and style I think. SMH: I prefer a new enum for lengthKind. That's the point of the property. It's much easier to say in the spec '...when dfdl:lengthKind is 'prefixed' or 'expression'...' than '...when dfdl:lengthKind is 'prefixed', or 'explicit' and dfdl:length is an expression and dfdl:unparseContentLength is 'xxx' ...'. Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com Please note: Contributions to the DFDL Workgroup's email discussions are subject to the OGF Intellectual Property Policy On Mon, Dec 8, 2014 at 11:53 AM, Steve Hanson <smh(a)uk.ibm.com> wrote: This is the email thread that discussed the behaviour of lengthKind 'explicit' where length is an expression, when unparsing. Erratum 2.100 had been raised and stated that this is an example of a variable length, and behaves like lengthKind 'prefixed'. The discussion below was around whether this captured all the use cases and should the dfdl:length expression be evaluated during unparsing in order to obtain a specified length to which the value could be padded (or truncated) in the same way as a fixed length. The conclusion was that the expression should not be evaluated. This is consistent with occursCount - the expression is not evaluated on unparsing. (There was a public comment on this area but it was just observing that the spec had not been fully updated to reflect 2.100) The use cases are numbered in the discussion below 1) to 4), with examples . Updated to reflect function name changes. The original proposal is also below, which was not adopted. However, an issue is that IBM DFDL already implements use case 1) by evaluating the expression on unparsing. I discovered this when I came to change the code to ensure 2.100 behaviour was followed. It is therefore likely that there are users who are relying on this behaviour in IBM DFDL. Coincidentally the same day I was asked by a user about the following use case. User has BCD data with length prefix. He wants to parse the data, do some processing then unparse the data, but it is not acceptable for the length of the data to change. Specifically, the BCD may start with 0s. When this is parsed as a decimal or integer, it has the effect of losing leading 0s so they need to be added back during unparsing. This is not possible with lengthKind 'prefixed' and nor is it possible with lengthKind 'expression' with erratum 2.100. User is currently treating the element as a 'prefixed' hexBinary blob to preserve the leading 0s. While this works for his use case, I am worried that the blob solution won't always be appropriate. Regards Steve Hanson Architect, IBM DFDL Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848 ----- Forwarded by Steve Hanson/UK/IBM on 08/12/2014 15:53 ----- From: Steve Hanson/UK/IBM To: dfdl-wg(a)ogf.org Date: 08/01/2013 18:06 Subject: Fw: [DFDL-WG] Action 183 - chicken-and-egg situation with lengths given by expressions Did not adopt the proposal below, and errata 2.100 remains as documented. Regards Steve Hanson Architect, Data Format Description Language (DFDL) Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848 ----- Forwarded by Steve Hanson/UK/IBM on 08/01/2013 18:05 ----- From: Steve Hanson/UK/IBM To: dfdl-wg(a)ogf.org, Date: 08/01/2013 14:44 Subject: Re: Fw: [DFDL-WG] Action 183 - chicken-and-egg situation with lengths given by expressions If we had the following we would have three behaviours which I think would cover the identified use cases. a) dfdl:lengthKind = "explicit", dfdl:length is an integer => length is specified on parsing & unparsing b) dfdl:lengthKind = "explicit", dfdl:length is an expression => length is specified on parsing & unparsing (expression must evaluate) - use cases 1) & 2) below - Mike's scenario where length is specified externally c) dfdl:lengthKind = "expression" (*new*), dfdl:length must be an expression => length is specified on parsing, but variable on unparsing (expression not evaluated) - new enum - use case 3) below - gives the erratum 2.100 behaviour - matches occursCountKind 'expression' behaviour Alternatively we leave errata 2.100 as it is and for Mike's scenario the application must do the padding before it passes the infoset values to the unparser. Regards Steve Hanson Architect, Data Format Description Language (DFDL) Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848 From: Steve Hanson/UK/IBM To: dfdl-wg(a)ogf.org, Date: 11/12/2012 10:36 Subject: Fw: [DFDL-WG] Action 183 - chicken-and-egg situation with lengths given by expressions The email thread which provided the material for the discussion which led to: 2.100. Section 12.3.1. State that when unparsing an element with lengthKind ‘explicit’ and where length is an expression, then the data in the Infoset is treated as variable length and not fixed length. The behaviour is the same as lengthKind ‘prefixed’. Regards Steve Hanson Architect, Data Format Description Language (DFDL) Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848 ----- Forwarded by Steve Hanson/UK/IBM on 16/11/2012 16:04 ----- From: Tim Kimber/UK/IBM@IBMGB To: dfdl-wg(a)ogf.org, Date: 11/09/2012 12:39 Subject: Re: [DFDL-WG] Action 183 - chicken-and-egg situation with lengths given by expressions Sent by: dfdl-wg-bounces(a)ogf.org Good point. The problem is that lengthKind-'explicit' is being used for two things: a) a length that is static b) a length that is calculated ...so the DFDL serializer must assume that the expression needs to be evaluated. For occursCountKind we have separate values for 'fixed' and 'expression'. If we did not, then occursCountKind would have the same problem except that it would affect defaulting rather than padding. regards, Tim Kimber, DFDL Team, Hursley, UK Internet: kimbert(a)uk.ibm.com Tel. 01962-816742 Internal tel. 37246742 From: Steve Hanson/UK/IBM@IBMGB To: dfdl-wg(a)ogf.org, Date: 11/09/2012 12:27 Subject: [DFDL-WG] Action 183 - chicken-and-egg situation with lengths given by expressions Sent by: dfdl-wg-bounces(a)ogf.org This mail is on the expected behaviour of the DFDL unparser when writing out a 'data' element the length of which is held in an earlier 'len' element. There are several scenarios, some straightforward and some that exhibit a chicken-and-egg behaviour. The principle of what happens is understood, the action is to make sure that the behaviour is explained in enough detail in the spec to enable implementations to be consistent. (Note - IBM DFDL does not yet support outputVaueCalc so has not hit this yet). Scenarios follow. The 'data' element shown is simple, but the same principles apply if it is complex. 1) 'len' is set from infoset - 'len' can be set in augmented infoset - No issue as 'data's length expression may be evaluated <xsd:element name="message1"> <xsd:complexType> <xsd:sequence> <xsd:element name="len" type="xsd:int" dfdl:lengthKind="explicit" dfdl:length="2" /> <xsd:element name="data" type="xsd:string" dfdl:length="{/message1/len}" dfdl:lengthKind="explicit" /> </xsd:sequence> </xsd:complexType> </xsd:element> 2) 'len' is set using outputValueCalc with fixed expression - When 'len's outputValueCalc is encountered, it can be evaluated then and there - 'len' can be set in augmented infoset - No issue as 'data's length expression may be evaluated <xsd:element name="message1"> <xsd:complexType> <xsd:sequence> <xsd:element name="len" type="xsd:int" dfdl:outputValueCalc="{10}" dfdl:lengthKind="explicit" dfdl:length="2" /> <xsd:element name="data" type="xsd:string" dfdl:length="{/message1/len}" dfdl:lengthKind="explicit" /> </xsd:sequence> </xsd:complexType> </xsd:element> 3) 'len' is set using outputValueCalc with reference 'data' (unpadded) - When 'len's outputValueCalc is encountered, it can not yet be evaluated as it depends on the length of 'data' - 'len' can not yet be set in augmented infoset - Problem as 'data's length expression can not be evaluated - But we do know the unpadded length of 'data' so 'len's outputValueCalc can now be evaluated - In turn this means that 'data's length expression can now be evaluated <xsd:element name="message1"> <xsd:complexType> <xsd:sequence> <xsd:element name="len" type="xsd:int" dfdl:outputValueCalc="{dfdl:valueLength(/message1/data)}" dfdl:lengthKind="explicit" dfdl:length="2" /> <xsd:element name="data" type="xsd:string" dfdl:length="{/message1/len}" dfdl:lengthKind="explicit" /> </xsd:sequence> </xsd:complexType> </xsd:element> 4) 'len' is set using outputValueCalc with reference 'data' (padded) - When 'len's outputValueCalc is encountered, it can not yet be evaluated as it depends on the length of 'data' - 'len' can not yet be set in augmented infoset - Problem as 'data's length expression can not be evaluated - We don't know the padded length of 'data' because we don't know 'len' - Problem: 'data's length expression can never be evaluated <xsd:element name="message1"> <xsd:complexType> <xsd:sequence> <xsd:element name="len" type="xsd:int" dfdl:outputValueCalc="{dfdl:contentLength(/message1/data)}" dfdl:lengthKind="explicit" dfdl:length="2" /> <xsd:element name="data" type="xsd:string" dfdl:length="{/message1/len}" dfdl:lengthKind="explicit" /> </xsd:sequence> </xsd:complexType> </xsd:element> Regards Steve Hanson Architect, Data Format Description Language (DFDL) Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848 From: Steve Hanson/UK/IBM To: dfdl-wg(a)ogf.org Date: 04/09/2012 17:31 Subject: Fw: Behaviour for lengthKind 'endOfparent' is still not fully specified DFDL WG call 4th Sept 2012: 1) Agreed that for binary data, only xs:hexBinary and packed/BCD allowed to have endOfParent 2) Agreed this is the correct behaviour when filling to a known length 3) Agreed this is the correct behaviour when filling to a known length 4) Agreed this is the correct behaviour when filling to a known length It was noted that lengthKind 'explicit' on the parent may not result in a known length if the length is an expression. This is an example of a more general chicken-and-egg situation with lengths given by expressions, for which outputValueCalc and DFDL functions unpaddedLength() were added can be used. Action raised to ensure that the behaviour of an implementation is fully defined by the spec. Regards Steve Hanson Architect, Data Format Description Language (DFDL) Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848 ----- Forwarded by Steve Hanson/UK/IBM on 04/09/2012 17:24 ----- From: Steve Hanson/UK/IBM To: dfdl-wg(a)ogf.org <dfdl-wg(a)ogf.org> Date: 04/09/2012 14:08 Subject: Behaviour for lengthKind 'endOfparent' is still not fully specified Noted when I reviewed latest spec - endOfParent and unparsing is not fully thought through. The spec today says that I can use endOfParent with binary data. There is a restriction in section 12.3.8, but it only applies when an element is endOfParent and its parent is lengthKind delimited. There are a couple of cases to consider: 1) Binary data of restricted length (see list in other email "proposed clarification/narrowing - delimited binary data should decimal"). I don't think it makes sense to allow these. We don't allow these binary reps for delimited. 2) Text data of variable length when unparsing. Box scenario. If the data in the infoset is shorter than the space in the box, what we do? I think we should pad to box length with appropriate padChar, according to justification, as that is effectively a 'specified length'. Error if textPadKind is 'none'. Use parent's lengthUnits. 3) HexBinary data of variable length when unparsing. Box scenario. If the data in the infoset is shorter than the space in the box, what we do? I think we should right-pad to box length with fill byte, as that is effectively a 'specified length'. 4) Packed/BCD binary data of variable length when unparsing. Box scenario. If the data in the infoset is shorter than the space in the box, what we do? I think we should pad to box length with zero bytes, according to justification, as that is effectively a 'specified length'. (Must be zero bytes and not fill byte as must be numeric in order to be parsed). In relation to 2 - 4, note that lengthKind 'endOfParent' can only be used with a parent lengthKind of 'explicit', 'pattern', 'prefixed' or 'endOfParent' or a choice with choiceLengthKind 'explicit', so the box scenario when unparsing therefore occurs only when lengthKind is 'explicit' or choiceLengthKind is 'explicit' - these are the cases when the length is known. Also note that when there are nested 'endOfParent' elements (which is allowed) then all padding must be done on the simple element (ie, the innermost element), to ensure that what is output can be parsed. Regards Steve Hanson Architect, Data Format Description Language (DFDL) Co-Chair, OGF DFDL Working Group IBM SWG, Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848 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 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(a)ogf.org https://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 -- dfdl-wg mailing list dfdl-wg(a)ogf.org https://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 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 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 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(a)ogf.org https://www.ogf.org/mailman/listinfo/dfdl-wg -- dfdl-wg mailing list dfdl-wg(a)ogf.org https://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 -- dfdl-wg mailing list dfdl-wg(a)ogf.org https://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 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 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

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