- dfdl-wg - lists.ogf.org

spec bug
by Mike Beckerle 13 Sep '12

13 Sep '12

section 7.4.1 in the example, the element named 'branchSimple' is not well formed (lacks type, for example). Just reporting this as a bug to fix next spin. -- Mike Beckerle | OGF DFDL WG Co-Chair Tel: 781-330-0412

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DFDL variables as path steps and with predicates
by Mike Beckerle 12 Sep '12

12 Sep '12

Currently the DFDL spec's grammar productions are quite liberal about where a VarRef can appear: PathExpr ::= ("/" RelativePathExpr?) | RelativePathExpr RelativePathExpr ::= StepExpr (("/") StepExpr)* StepExpr ::= FilterExpr | AxisStep AxisStep ::= (ReverseStep | ForwardStep) Predicate FilterExpr ::= PrimaryExpr Predicate Predicate ::= "[" Expr "]" PrimaryExpr ::= Literal | *VarRef* | ParenthesizedExp in terms of XPath 2.0 syntax, you could write $x/a/b/$y/../$z. However, the spec also says the type of a variable can only be one of the simple types allowed by DFDL only. So no path steps in the sense of children are meaningful after a DFDL variable. Furthermore, variables are all declared at top level. There is no notion of parent nodes for variable values; hence, a/$x is meaningless (or means the same as $x by itself), and $x/.. is similarly meaningless. But, a variable reference can be followed by a predicate. The resulting node set, would either be one node, containing the value of the variable, or zero nodes. For example is { fn:exists($x[. eq 3] } is presumably a boolean valued expression true if variable x's value is 3. Are there any issues here with predicates?? Should we update the expression language productions to enable only sensible use of DFDL variables in expressions or leave it to match XPath 2.0's more general syntax. If we update the productions should we disallow predicates after variable references also? This loses no expressive power, you can still write { if ($x eq 3) then true else false }, which is to say I think there is no inherent capability lost if we require variable references to be atomic expressions that produce exactly a single node value. ...mikeb -- Mike Beckerle | OGF DFDL WG Co-Chair Tel: 781-330-0412

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minor spec correction Appendix 33
by Mike Beckerle 11 Sep '12

11 Sep '12

These tables are awesomely useful, but very badly labelled. Columns Data and Result should be labeled "Logical Data" and "Physical Data". ...mikeb -- Mike Beckerle | OGF DFDL WG Co-Chair Tel: 781-330-0412

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OGF DFDL WG Call Minutes 2012-09-11
by Steve Hanson 11 Sep '12

11 Sep '12

Please find minutes from the above call on GridForge at https://forge.ogf.org/sf/docman/do/downloadDocument/projects.dfdl-wg/docman… Errata document is now at v010 here: http://forge.gridforum.org/sf/go/doc16280?nav=1 Regards Steve Hanson Architect, DFDL, IBM SWG Co-Chair, OGF DFDL Working Group Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848

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Expressions and Variables: Rationale language
by Mike Beckerle 11 Sep '12

11 Sep '12

Some rationale around the expression language and single-assignment variables. Not sure if this helps, but I'm trying not to rewrite a thesis on the topic here. DFDL is intended to be a description language. That is, the capture of a data format should be as descriptive/declarative as possible. An additional quite critical goal for DFDL is that it allows very high performance implementations, including use of parallel processing wherever possible. DFDL contains an expression language with variables for use in creating parameterized DFDL schemas. However, the way variables can be used in DFDL is quite constrained. Specifically, the variables are single-assignment. Single-assignment variables solve a number of problems. First, they keep the schema more declarative, because the name of a variable represents a value, not a location. Before assignment, the value is not yet known, after the assignment the value is known, but the consumer of the value need only know the name, and need not be aware of the mechanism by which it gets its value or when. Second, single-assignment variables avoid over-constraining the implementation, thereby preserving the potential for high-performance and parallel processing. Some digression is useful here: Any variable creates a data dependency in order of processing. The part of the schema reading/using the variable's value depends upon the data value coming from the part of the schema providing that value. This kind of data dependency is inherent and inescapable. Values must be created before they can be used. However, if you consider a variable to be a location that can be assigned repeatedly, then things are more complex because you not only have data dependency on the value (one part of the schema writes the location, another reads that location), but you have the dependency in the other direction: you must read the location before it can be used again for the * next* value. This is usually called anti-dependency. Anti-dependency is the enemy of high-performance and parallel execution. It forces specific and artificial sequential ordering on things that is due to the way variable names are allocated to storage locations. If variables are single-assignment only, then only data-dependencies exist. Anti-dependencies don't exist, and implementations are free to work in any way consistent with the (inescapable) data dependencies. -- Mike Beckerle | OGF DFDL WG Co-Chair Tel: 781-330-0412

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ICU Parsing Behaviour
by Richard Schofield 11 Sep '12

11 Sep '12

Attached below is a brief summary of ICU's number parsing behaviour (data collected using ICU4C 49.1.2) The following data will be parsed successfully regardless of the pattern or strict/lenient parsing mode Digits 0-9 Decimal Separator Exponent Separator Grouping separators are only permitted in the data, if specified in the pattern When in STRICT mode the following will cause a parse failure (using a pattern of "#,##0.#") Leading or doubled grouping separators ',123' and '1,,234" fail Groups of incorrect length when grouping is used '1,23' and '1234,567' fail, but '1234' passes Grouping separators used in numbers followed by exponents '1,234E5' fails, but '1234E5' and '1,234E' pass ('E' is not an exponent when not followed by a number) 'Other' characters in the pattern must be present in the data. For example, with a pattern of 'z'## :- z12 will parse successfully, 12 will only parse successfully in lenient mode. Regards Richard 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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Action 183 - chicken-and-egg situation with lengths given by expressions
by Steve Hanson 11 Sep '12

11 Sep '12

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:unpaddedLength(/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:representationLength(/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

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OGF DFDL WG Call Agenda 2012-09-11
by Steve Hanson 11 Sep '12

11 Sep '12

Please find agenda for the above call attached (there is a problem with GridForge today) 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

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clarification wanted: fixed values
by Mike Beckerle 06 Sep '12

06 Sep '12

The spec states that the fixed facet is only used for validation. That is, it works like default in that it supplies a default that can be used when parsing and unparsing, but the comparison of an existing data value with the schema-specified fixed value is only done for validation. This means that a value not agreeing with the fixed value specified in the schema would never cause backtracking. Is this right? It seems awkward to me that I have to use a dfdl:assert annotation to achieve this. That said, however, I can achieve the behaviour I need. it's just more verbose than I wanted. Is this what the current IBM implementation does? Thanks -- Mike Beckerle | OGF DFDL WG Co-Chair Tel: 781-330-0412

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OGF DFDL WG Call Minutes 2012-09-04
by Steve Hanson 04 Sep '12

04 Sep '12

Please find minutes from the above call on GridForge at https://forge.ogf.org/sf/docman/do/downloadDocument/projects.dfdl-wg/docman… Errata document is now at v010 here: http://forge.gridforum.org/sf/go/doc16280?nav=1 Regards Steve Hanson Architect, DFDL, IBM SWG Co-Chair, OGF DFDL Working Group Hursley, UK smh(a)uk.ibm.com tel:+44-1962-815848

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