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OGF DFDL WG Call Agenda 2014-11-04
by Steve Hanson 03 Nov '14

03 Nov '14

Please find agenda for call on Redmine at http://redmine.ogf.org/dmsf_files/13370?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 2014-10-28
by Steve Hanson 03 Nov '14

03 Nov '14

Please find minutes from the above call at http://redmine.ogf.org/dmsf_files/13369?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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elementFormDefault and the form attribute on element declarations
by Mike Beckerle 03 Nov '14

03 Nov '14

Neither the term "elementFormDefault" nor the term "unqualified" appear in the DFDL Spec. So we're silent about whether these are allowed or not in DFDL schemas. We should specify what of this XML Schema behavior is allowed, which I believe means add a line to each of the lists in section 5.1 of things used and not-used/reserved from XML Schema. FYI: Today the Daffodil implementation implements elementFormDefault on the xs:schema but not the form attribute on element declarations. We have tests that exercise elementFormDefault in qualified and unqualified and not specified at all (which defaults to "unqualified" behavior in XSD, so we're consistent with that.) 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 <http://www.ogf.org/About/abt_policies.php>

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Action 274 - on qnames in path expressions in DFDL
by Mike Beckerle 03 Nov '14

03 Nov '14

I did some experiments with the XML validation built into eclipse, and the key constraint, which has paths (in the selector and field attributes) that refer to other parts of the XML infoset/document and so involve the names of elements. I also have been reading the XPath 2.0 specs including the formal semantics. To my interpretation XPath 2.0 is pretty explicit: An element or type QName consisting only of a local part NCName expands to the default element/type namespace and the local part. They don't qualify this in any way that I can find for the names used in path steps. The formal semantics is pretty hard to understand, but this detail seems to be swept under the rug. There would need to be specific treatment of this in the naming environment, but I cannot find this. There is discussion of name resolution in some of their judgements, but nothing I can see that creates an exception for names in path steps. (Called name tests) What I was looking for was language that specifies something about a non-prefixed name in a path step and that it is NOT augmented by the default namespace. I could find no such exception. But if I am right and this detail isn't there, i.e., If there is no such exception, then the implementation of XPath in eclipse (which is xerces I believe) is incorrect in the way it resolves names that appear in path steps. Here's how it works according to eclipse: In xpath expressions in the selectors and fields of unique and key constraints, xmlns (the default namespace) is not considered as implicitly augmenting unqualified names that appear in path steps. An identifier in a path step that has no prefix (e.g., 'foo' in the path './p1:bar/foo/p2:baz') is always interpreted as identifying either 1) a child element defined by a local element declaration with form "unqualified". or 2) this corner case: a child element defined by an element reference to a global element declaration but only when that global element declaration has no effective target namespace. (Use of 'effective' here rules out an element decl inside a schema document that itself has no target namespace but is included into a schema that has one. Such an element declaration effectively has a target namespace, so this corner case doesn't apply.) Case (2) here is a rather obscure corner case, but there nevertheless. In no case (that I could construct) does the name in a path step get augmented by a schema's default namespace (defined by xmlns="...whatever..."). The above is true for names without prefix appearing in path steps of expressions. The QNames that are used in an XML schema to reference a global declaration or definition (in the ref of an element ref, type attribute in a type reference, base in a simple type derivation, etc.) are different. Those names DO pickup a default namespace if one is defined and they have no explicit prefix themselves. This creates a corner case for these references (to global decls/defs) which is if a definition/declaration appears in no effective target namespace, then there is no way to reference it at all from a schema that has a default namespace definition surrounding the point of reference. There is no syntactic way to turn-off use of a default namespace. (The semantics of xpath allows for a "none" default namespace definition, but there is no xml syntax for expressing explicitly this "none". It is simply what you have if there is no prefix and no default namespace). You can change which namespace the default is, but there's no way to say explicitly "I meant this QName reference to be to something not in any namespace. Unless/until we can find language in some XML Schema spec indicating how path step names (name tests) are specifically resolved, then the above is just "how one system does it." But we may end up having to follow precedent here from implementations. 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 <http://www.ogf.org/About/abt_policies.php>

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clarification: fn:exactly-one function
by Mike Beckerle 03 Nov '14

03 Nov '14

According to the DFDL spec, fn:exactly-one returns "True if the provided sequence contains exactly one node/value," which suggests that the function would return false if the sequence contains > or < 1 node/value. The XPath description states that fn:exactly-one "returns $arg if it contains exactly one item. Otherwise, raises an error." It seems of value to have a true/false result, because something that raises an error like this can only be used as an assertion effectively. On the other hand, that's not what XPath does. 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 <http://www.ogf.org/About/abt_policies.php>

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Fw: Action 258 - data where inactive escape character is to be retained
by Steve Hanson 31 Oct '14

31 Oct '14

On last WG call there was still some concern about the names used. We will go with the proposal unless better names are suggested. 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 31/10/2014 11:18 ----- From: Steve Hanson/UK/IBM To: dfdl-wg(a)ogf.org Date: 24/10/2014 13:22 Subject: Re: Fw: [DFDL-WG] Action 258 - data where inactive escape character is to be retained Proposal updated below to reflect recent WG calls - changes in red type. 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: dfdl-wg(a)ogf.org Date: 28/08/2014 15:47 Subject: Fw: [DFDL-WG] Action 258 - data where inactive escape character is to be retained Strawman proposal for action 258. 258 Consider allowing more flexible escapeCharacter schemes (Mike) 6/5: Motivated by example of an escape character which is active when in front of an in-scope delimiter, but not when in front of another character. 20/5: Can't model Mike's example with current facilities, but Mike's example is a generalisation of a particular MITRE example. Do we really need this? Jonathan to follow up. 3/6: Closed. Jonathan has provided the background to the MITRE example which was really about initiators and terminators. The generalised use case is perhaps speculative, so it was agreed not to change the DFDL spec to handle this unless a concrete use case emerges. 17/6: Re-opened. vCard 3.0 (http://tools.ietf.org/html/rfc2426) is an example of a format that exhibits the need for this. Need a proposal to handle this case, and which fits in with the existing extraEscapedCharacters and escapeEscapeCharacter property. Noted that using lengthKind 'pattern' is sometimes a way of working round this kind of thing. ... 15/7: No progress 22/7: Steve has started to write up a proposal. ... 26/8: No further progress 2/9: Strawman proposal sent by Steve for comment. Concern over name of new property. Review for next week. ... 16/9: No further progress 23/9: Discussed the naming issue, Steve to send revised proposal. Candidate for deferral to 1.1 ? 14/10: Agreed that it would be good to be able to handle vCard 3.0. With Steve to revise the proposal. New property dfdl:applyEscapeCharacter added. The description of dfdl:escapeKind is updated. No changes to dfdl:generateEscapeBlock but I've added it below by way of comparison. Property Name Description escapeKind Enum Valid values 'escapeCharacter', 'escapeBlock' The type of escape mechanism defined in the escape scheme When 'escapeCharacter': On unparsing a single character of the data is escaped by adding a dfdl:escapeCharacter or dfdl:escapeEscapeCharacter immediately before it. The characters to escape are determined by property dfdl:escapeCharacterPolicy. On parsing any in-scope terminating delimiter encountered in the data is not interpreted as such when it is immediately preceded by the dfdl:escapeCharacter (when not itself preceded by the dfdl:escapeEscapeCharacter). Occurrences of the dfdl:escapeCharacter and dfdl:escapeEscapeCharacter are removed from the data as determined by property dfdl:escapeCharacterPolicy unless the dfdl:escapeCharacter is preceded by the dfdl:escapeEscapeCharacter, or the dfdl:escapeEscapeCharacter does not precede the dfdl:escapeCharacter, respectively. When 'escapeBlock': On unparsing the entire data are escaped by adding dfdl:escapeBlockStart to the beginning and dfdl:escapeBlockEnd to the end of the data. The data is either always escaped or escaped when needed as specified by dfdl:generateEscapeBlock. If the data is escaped and contains the dfdl:escapeBlockEnd then first character of each appearance of the dfdl:escapeBlockEnd is escaped by the dfdl:escapeEscapeCharacter. On parsing the dfdl:escapeBlockStart string must be the first characters in the (trimmed) data in order to activate the escape scheme. The dfdl:escapeBlockStart string is removed from the beginning of the data. Until a matching dfdl:escapeBlockEnd string (that is, one not preceded by the dfdl:escapeEscapeCharacter) is found in the data, any in-scope terminating delimiter encountered in the data is not interpreted as such, and any dfdl:escapeEscapeCharacters are removed when they precede an dfdl:escapeBlockEnd string. The matching dfdl:escapeBlockEnd string is removed from the data.. The matching dfdl:escapeBlockEnd does not have to be the last characters in the (trimmed) data in order to de-activate the escape scheme. A dfdl:escapeBlockStart occurring anywhere in the data other than the first characters has no significance. Annotation: dfdl:escapeScheme escapeCharacterPolicy Enum Valid values 'all', 'delimiters' Controls when escape characters are removed during parsing, and output during unparsing, when dfdl:escapeKind is 'escapeCharacter'. When 'all': During unparsing the following are escaped as described in dfdl:escapeKind when they are in the data. · Any in-scope terminating delimiter by escaping its first character. · dfdl:escapeCharacter (escaped by dfdl:escapeEscapeCharacter) · any dfdl:extraEscapedCharacters During parsing, occurrences of dfdl:escapeCharacter and dfdl:escapeEscapeCharacter are interpreted and removed from the data as described in dfdl:escapeKind. When 'delimiters': During unparsing the following are escaped as described in dfdl:escapeKind when they are in the data. · Any in-scope terminating delimiter by escaping its first character. · dfdl:escapeCharacter (escaped by dfdl:escapeEscapeCharacter) During parsing, occurrences of dfdl:escapeCharacter and dfdl:escapeEscapeCharacter are interpreted and removed from the data as described in dfdl:escapeKind, except that dfdl:escapeCharacter is only removed when it immediately precedes an in-scope terminating delimiter. Annotation: dfdl:escapeScheme generateEscapeBlock Enum Valid values 'always', 'whenNeeded' Controls when escaping is used on unparsing when dfdl:escapeKind is 'escapeBlock'. If 'always' then escaping always occurs as described in dfdl:escapeKind. If 'whenNeeded' then escaping occurs as described in dfdl:escapeKind when the data contains any of the following: · any in-scope terminating delimiter · dfdl:escapeBlockStart at the start of the data · any dfdl:extraEscapedCharacters Annotation: dfdl:escapeScheme 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 22/07/2014 15:10 ----- From: Steve Hanson/UK/IBM To: "Cranford, Jonathan W." <jcranford(a)mitre.org>, Cc: "dfdl-wg(a)ogf.org" <dfdl-wg(a)ogf.org> Date: 13/06/2014 17:28 Subject: Re: [DFDL-WG] data where inactive escape character is to be retained I think I have come across a concrete example of this. It's from a standard called vCard 3.0 (RFC 2426 - http://tools.ietf.org/html/rfc2426) A backslash is used to a) escape itself; b) escape in-scope delimiters; c) indicate an embedded linefeed. The backslash would need removing for a) and b) but not for c). ESCAPED-CHAR = "\\" / "\;" / "\," / "\n" / "\N") ; \\ encodes \, \n or \N encodes newline ; \; encodes ;, \, encodes , 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: "Cranford, Jonathan W." <jcranford(a)mitre.org>, Cc: "dfdl-wg(a)ogf.org" <dfdl-wg(a)ogf.org>, dfdl-wg-bounces(a)ogf.org, Mike Beckerle <mbeckerle.dfdl(a)gmail.com> Date: 04/06/2014 08:53 Subject: Re: [DFDL-WG] data where inactive escape character is to be retained WG call 3rd June: The generalised use case is perhaps speculative, so it was agreed not to change the DFDL spec to handle this unless a concrete use case emerges. 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: "Cranford, Jonathan W." <jcranford(a)mitre.org> To: Mike Beckerle <mbeckerle.dfdl(a)gmail.com>, "dfdl-wg(a)ogf.org" <dfdl-wg(a)ogf.org>, Date: 20/05/2014 18:11 Subject: Re: [DFDL-WG] data where inactive escape character is to be retained Sent by: dfdl-wg-bounces(a)ogf.org All, I’ll chime in with an observation and few more details on how Roger Costello got around a similar problem. Observation An escape block allows the escapeBlockEnd to be escaped with the escapeEscapeCharacter, while allowing the escapeEscapeCharacter itself to appear in the data without any special semantics as long as it is NOT followed by escapeBlockEnd. (From section 13.2.1 of the spec: “On parsing the dfdl:escapeBlockStart is removed from the beginning of the data and dfdl:escapeBlockEnd is removed from end of the data and any dfdl:escapeEscapeCharacters are removed when they precede a dfdl:escapeBlockEnd.”) This is really similar to the problem that Mike posed to the group below, where an escape character is sometimes an escape character but sometimes isn’t. While an escape block might not be suitable in all circumstances, the original problem that sparked Mike’s post was amenable to using an escape block, and that is how Roger Costello got around the problem. Some more details Roger Costello was using a quotation mark (“) as the initiator and terminator for quoted values in a data format. In this format, quotation marks can be escaped with a backslash (\); however, within a quoted string, the data could have a backslash as a normal data character (e.g. \n, representing two characters, not a single newline character). Roger posed his challenge to the Daffodil team, and then Mike created the example below to demonstrate the problem to the DFDL WG. In contrast to Mike’s example, Roger was having the problem with initiators and terminators, not a separator. At the time, we thought that that an escape block couldn’t be applied to the data format in question, so Mike may have altered the problem in order to prevent an escape block from clouding the issue as posed to the WG. It turns out, after more analysis, that an escape block could be used, and that solved the problem: escapeBlockStart=”"” escapeBlockEnd=”"” escapeEscapeCharacter=”\” Closing Observations In general, DFDL supports two different escape schemes with different behavior for the escape character. * When escapeKind=”escapeCharacter”, the escape character is always an escape character. * When escapeKind=”escapeBlock”, the escape character (escapeEscapeCharacter) is only an escape character in front of escapeBlockEnd. In this case, we were able to use an escape block to model the data format. While there may be a data format that has a character that is sometimes an escape character and sometimes isn’t, without a real world example, I echo Mike’s hesitance to add this feature to DFDL. HTH, Jonathan Cranford From: dfdl-wg-bounces(a)ogf.org [mailto:dfdl-wg-bounces@ogf.org] On Behalf Of Mike Beckerle Sent: Friday, May 02, 2014 2:47 PM To: dfdl-wg(a)ogf.org Subject: [DFDL-WG] data where inactive escape character is to be retained We have data that has ; as separator and has fields that look like this: abcd \; efgh That's a single field. The backslash escapes the ; so that the data is abcd ; efgh. This same data set also has abcd \n efgh Here the backslash precedes an ordinary non-delimiter. The data is supposed to be abcd \n efgh. That is, this data set requires the backslash to be retained in the data when it is not preceding the start of a delimiter. Am I missing something or is it impossible to model this? It would seem there needs to be a flag to indicate whether the escape characters that don't actually escape a delimiter are to be retained or not. 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 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

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minor/typographical - fn prefix namespace not in spec
by Mike Beckerle 28 Oct '14

28 Oct '14

The URI corresponding to the xpath functions namespace http://www.w3.org/2005/xpath-functions <https://exchange10.columbia.tresys.com/owa/redir.aspx?C=5e667bd287024022963…> is not in the DFDL spec. I am assuming where we are borrowing the exact XPath function behavior the namespace is the xpath functions URI, not some DFDL-specific URI. 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 <http://www.ogf.org/About/abt_policies.php>

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Re: [DFDL-WG] Catch 22.for EVDP & NVDP ?
by Steve Hanson 28 Oct '14

28 Oct '14

Thinking through the implications of having EVDP not apply if content length can not be zero: 1) Cases are dfdl:lengthKind 'explicit', dfdl:length not an expression and not zero, and (simple only) dfdl:lengthKind 'implicit' and maxLength facet not zero. 2) Does it mean a) that there is no concept of an empty representation, or b) that there is but it is not subject to EVDP and 'effective' EVDP is 'none' ? - If b) that does not fix the issue around initiatedContent, - if a) it means not finding the element must be taken as missing which implies no default value can be applied. Hmm 3) What about NVDP ? Should we be disallowing the use of %ES; as a nil value for these cases as well ? 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: Mike Beckerle <mbeckerle.dfdl(a)gmail.com> Cc: "dfdl-wg(a)ogf.org" <dfdl-wg(a)ogf.org> Date: 17/09/2014 15:44 Subject: Re: [DFDL-WG] Catch 22.for EVDP & NVDP ? Having thought this through I think that you are correct. If the content length can never be 0 then EVDP does not apply. I think IBM DFDL is issuing an error when it should not be. 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: Mike Beckerle <mbeckerle.dfdl(a)gmail.com> To: Steve Hanson/UK/IBM@IBMGB, Cc: "dfdl-wg(a)ogf.org" <dfdl-wg(a)ogf.org> Date: 09/09/2014 15:37 Subject: Re: [DFDL-WG] Catch 22.for EVDP & NVDP ? Interesting. To me if lengthKind is explicit, and non-variable (i.e., is fixed length), then EVDP doesn't apply, because by definition, such a representation is not ever empty. I would assume that EVDP would be ignored in such a case, and an implementation might even generate warnings if dfdl:emptyValueDelimiterPolicy appeared directly on such an element or simpleType where a fixed length is also expressed. This is one of the challenges that having lengthKind 'explicit' which handles both the fixed length, and variable-length using an expression, creates. Even though we don't have a lengthKind 'fixed', we still have fixed-length as a concept, and some other features interact with fixed length, like empty values. 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 Tue, Sep 2, 2014 at 10:31 AM, Steve Hanson <smh(a)uk.ibm.com> wrote: <xs:element name="choiceGroup" dfdl:lengthKind="implicit"> <xs:complexType> <xs:choice dfdl:choiceLengthKind="implicit" dfdl:initiatedContent="yes"> <xs:element name="myNum1" type="xs:int" dfdl:lengthKind="explicit" dfdl:length="2" dfdl:textNumberPattern="#0" dfdl:initiator="num:" dfdl:terminator="~" /> > <xs:element name="myText1" type="xs:string" dfdl:lengthKind="explicit" dfdl:length="2" dfdl:initiator="text:" dfdl:terminator="~" /> </xs:choice> </xs:complexType> </xs:element> The above model is a choice of two elements, each of which is fixed length and has an initiator and terminator. Because the elements are fixed length, I must set dfdl:emptyValueDelimiterPolicy (EVDP) to be 'none' **. I also want to discriminate using the initiator, so I set dfdl:initiatedContent 'yes' on the choice, so I must set EVDP to 'initiator' or 'both' ++. (Same for NVDP if nillable). Catch 22. ** 'none' because the only valid empty representation is that there is nothing there at all. The element is fixed length X, so if the delimiters are present then the content must be length X and can't be zero length. ++ 'initiator' or 'both' because an initiator must always be present when dfdl:initiatedContent 'yes'. The implication is that I can't use dfdl:initiatedContent for this choice. While I can switch off nillable to avoid the error with NVDP, there is no other way of avoiding the EVDP error. 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 -- 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 Agenda 2014-10-28
by Steve Hanson 27 Oct '14

27 Oct '14

Please find agenda for call on Redmine at http://redmine.ogf.org/dmsf_files/13369?download= Note that clocks have gone back in UK, but not yet in US, so call time in US is 12 noon Eastern. If that is a problem to anyone please let me know and we can re-schedule. 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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Re: [DFDL-WG] Fw: Action 258 - data where inactive escape character is to be retained
by Steve Hanson 24 Oct '14

24 Oct '14

Proposal updated below to reflect recent WG calls - changes in red type. 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: dfdl-wg(a)ogf.org Date: 28/08/2014 15:47 Subject: Fw: [DFDL-WG] Action 258 - data where inactive escape character is to be retained Strawman proposal for action 258. 258 Consider allowing more flexible escapeCharacter schemes (Mike) 6/5: Motivated by example of an escape character which is active when in front of an in-scope delimiter, but not when in front of another character. 20/5: Can't model Mike's example with current facilities, but Mike's example is a generalisation of a particular MITRE example. Do we really need this? Jonathan to follow up. 3/6: Closed. Jonathan has provided the background to the MITRE example which was really about initiators and terminators. The generalised use case is perhaps speculative, so it was agreed not to change the DFDL spec to handle this unless a concrete use case emerges. 17/6: Re-opened. vCard 3.0 (http://tools.ietf.org/html/rfc2426) is an example of a format that exhibits the need for this. Need a proposal to handle this case, and which fits in with the existing extraEscapedCharacters and escapeEscapeCharacter property. Noted that using lengthKind 'pattern' is sometimes a way of working round this kind of thing. ... 15/7: No progress 22/7: Steve has started to write up a proposal. ... 26/8: No further progress 2/9: Strawman proposal sent by Steve for comment. Concern over name of new property. Review for next week. ... 16/9: No further progress 23/9: Discussed the naming issue, Steve to send revised proposal. Candidate for deferral to 1.1 ? 14/10: Agreed that it would be good to be able to handle vCard 3.0. With Steve to revise the proposal. New property dfdl:applyEscapeCharacter added. The description of dfdl:escapeKind is updated. No changes to dfdl:generateEscapeBlock but I've added it below by way of comparison. Property Name Description escapeKind Enum Valid values 'escapeCharacter', 'escapeBlock' The type of escape mechanism defined in the escape scheme When 'escapeCharacter': On unparsing a single character of the data is escaped by adding a dfdl:escapeCharacter or dfdl:escapeEscapeCharacter immediately before it. The characters to escape are determined by property dfdl:escapeCharacterPolicy. On parsing any in-scope terminating delimiter encountered in the data is not interpreted as such when it is immediately preceded by the dfdl:escapeCharacter (when not itself preceded by the dfdl:escapeEscapeCharacter). Occurrences of the dfdl:escapeCharacter and dfdl:escapeEscapeCharacter are removed from the data as determined by property dfdl:escapeCharacterPolicy unless the dfdl:escapeCharacter is preceded by the dfdl:escapeEscapeCharacter, or the dfdl:escapeEscapeCharacter does not precede the dfdl:escapeCharacter, respectively. When 'escapeBlock': On unparsing the entire data are escaped by adding dfdl:escapeBlockStart to the beginning and dfdl:escapeBlockEnd to the end of the data. The data is either always escaped or escaped when needed as specified by dfdl:generateEscapeBlock. If the data is escaped and contains the dfdl:escapeBlockEnd then first character of each appearance of the dfdl:escapeBlockEnd is escaped by the dfdl:escapeEscapeCharacter. On parsing the dfdl:escapeBlockStart string must be the first characters in the (trimmed) data in order to activate the escape scheme. The dfdl:escapeBlockStart string is removed from the beginning of the data. Until a matching dfdl:escapeBlockEnd string (that is, one not preceded by the dfdl:escapeEscapeCharacter) is found in the data, any in-scope terminating delimiter encountered in the data is not interpreted as such, and any dfdl:escapeEscapeCharacters are removed when they precede an dfdl:escapeBlockEnd string. The matching dfdl:escapeBlockEnd string is removed from the data.. The matching dfdl:escapeBlockEnd does not have to be the last characters in the (trimmed) data in order to de-activate the escape scheme. A dfdl:escapeBlockStart occurring anywhere in the data other than the first characters has no significance. Annotation: dfdl:escapeScheme escapeCharacterPolicy Enum Valid values 'all', 'delimiters' Controls when escape characters are removed during parsing, and output during unparsing, when dfdl:escapeKind is 'escapeCharacter'. When 'all': During unparsing the following are escaped as described in dfdl:escapeKind when they are in the data. · Any in-scope terminating delimiter by escaping its first character. · dfdl:escapeCharacter (escaped by dfdl:escapeEscapeCharacter) · any dfdl:extraEscapedCharacters During parsing, occurrences of dfdl:escapeCharacter and dfdl:escapeEscapeCharacter are interpreted and removed from the data as described in dfdl:escapeKind. When 'delimiters': During unparsing the following are escaped as described in dfdl:escapeKind when they are in the data. · Any in-scope terminating delimiter by escaping its first character. · dfdl:escapeCharacter (escaped by dfdl:escapeEscapeCharacter) During parsing, occurrences of dfdl:escapeCharacter and dfdl:escapeEscapeCharacter are interpreted and removed from the data as described in dfdl:escapeKind, except that dfdl:escapeCharacter is only removed when it immediately precedes an in-scope terminating delimiter. Annotation: dfdl:escapeScheme generateEscapeBlock Enum Valid values 'always', 'whenNeeded' Controls when escaping is used on unparsing when dfdl:escapeKind is 'escapeBlock'. If 'always' then escaping always occurs as described in dfdl:escapeKind. If 'whenNeeded' then escaping occurs as described in dfdl:escapeKind when the data contains any of the following: · any in-scope terminating delimiter · dfdl:escapeBlockStart at the start of the data · any dfdl:extraEscapedCharacters Annotation: dfdl:escapeScheme 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 22/07/2014 15:10 ----- From: Steve Hanson/UK/IBM To: "Cranford, Jonathan W." <jcranford(a)mitre.org>, Cc: "dfdl-wg(a)ogf.org" <dfdl-wg(a)ogf.org> Date: 13/06/2014 17:28 Subject: Re: [DFDL-WG] data where inactive escape character is to be retained I think I have come across a concrete example of this. It's from a standard called vCard 3.0 (RFC 2426 - http://tools.ietf.org/html/rfc2426) A backslash is used to a) escape itself; b) escape in-scope delimiters; c) indicate an embedded linefeed. The backslash would need removing for a) and b) but not for c). ESCAPED-CHAR = "\\" / "\;" / "\," / "\n" / "\N") ; \\ encodes \, \n or \N encodes newline ; \; encodes ;, \, encodes , 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: "Cranford, Jonathan W." <jcranford(a)mitre.org>, Cc: "dfdl-wg(a)ogf.org" <dfdl-wg(a)ogf.org>, dfdl-wg-bounces(a)ogf.org, Mike Beckerle <mbeckerle.dfdl(a)gmail.com> Date: 04/06/2014 08:53 Subject: Re: [DFDL-WG] data where inactive escape character is to be retained WG call 3rd June: The generalised use case is perhaps speculative, so it was agreed not to change the DFDL spec to handle this unless a concrete use case emerges. 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: "Cranford, Jonathan W." <jcranford(a)mitre.org> To: Mike Beckerle <mbeckerle.dfdl(a)gmail.com>, "dfdl-wg(a)ogf.org" <dfdl-wg(a)ogf.org>, Date: 20/05/2014 18:11 Subject: Re: [DFDL-WG] data where inactive escape character is to be retained Sent by: dfdl-wg-bounces(a)ogf.org All, I’ll chime in with an observation and few more details on how Roger Costello got around a similar problem. Observation An escape block allows the escapeBlockEnd to be escaped with the escapeEscapeCharacter, while allowing the escapeEscapeCharacter itself to appear in the data without any special semantics as long as it is NOT followed by escapeBlockEnd. (From section 13.2.1 of the spec: “On parsing the dfdl:escapeBlockStart is removed from the beginning of the data and dfdl:escapeBlockEnd is removed from end of the data and any dfdl:escapeEscapeCharacters are removed when they precede a dfdl:escapeBlockEnd.”) This is really similar to the problem that Mike posed to the group below, where an escape character is sometimes an escape character but sometimes isn’t. While an escape block might not be suitable in all circumstances, the original problem that sparked Mike’s post was amenable to using an escape block, and that is how Roger Costello got around the problem. Some more details Roger Costello was using a quotation mark (“) as the initiator and terminator for quoted values in a data format. In this format, quotation marks can be escaped with a backslash (\); however, within a quoted string, the data could have a backslash as a normal data character (e.g. \n, representing two characters, not a single newline character). Roger posed his challenge to the Daffodil team, and then Mike created the example below to demonstrate the problem to the DFDL WG. In contrast to Mike’s example, Roger was having the problem with initiators and terminators, not a separator. At the time, we thought that that an escape block couldn’t be applied to the data format in question, so Mike may have altered the problem in order to prevent an escape block from clouding the issue as posed to the WG. It turns out, after more analysis, that an escape block could be used, and that solved the problem: escapeBlockStart=”"” escapeBlockEnd=”"” escapeEscapeCharacter=”\” Closing Observations In general, DFDL supports two different escape schemes with different behavior for the escape character. * When escapeKind=”escapeCharacter”, the escape character is always an escape character. * When escapeKind=”escapeBlock”, the escape character (escapeEscapeCharacter) is only an escape character in front of escapeBlockEnd. In this case, we were able to use an escape block to model the data format. While there may be a data format that has a character that is sometimes an escape character and sometimes isn’t, without a real world example, I echo Mike’s hesitance to add this feature to DFDL. HTH, Jonathan Cranford From: dfdl-wg-bounces(a)ogf.org [mailto:dfdl-wg-bounces@ogf.org] On Behalf Of Mike Beckerle Sent: Friday, May 02, 2014 2:47 PM To: dfdl-wg(a)ogf.org Subject: [DFDL-WG] data where inactive escape character is to be retained We have data that has ; as separator and has fields that look like this: abcd \; efgh That's a single field. The backslash escapes the ; so that the data is abcd ; efgh. This same data set also has abcd \n efgh Here the backslash precedes an ordinary non-delimiter. The data is supposed to be abcd \n efgh. That is, this data set requires the backslash to be retained in the data when it is not preceding the start of a delimiter. Am I missing something or is it impossible to model this? It would seem there needs to be a flag to indicate whether the escape characters that don't actually escape a delimiter are to be retained or not. 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 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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