April 2012 - dfdl-wg - lists.ogf.org

Fw: Action 145: 'dispatch' way of discriminating a choice for better performance
by Steve Hanson 11 Apr '12

11 Apr '12

Updated to reflect the outcome of DFDL WG call on 5th April. Revised details: A new dfdl:element property is added called dfdl:elementID of type 'DFDL String Literal'. This provides a single alternative name for the element. Only allowed on local element and global element, not on element reference or simple type. A new dfdl:choice property is added called dfdl:choiceBranchRef of type 'DFDL Expression'. The expression must evaluate to a DFDL String Literal. The resultant string must match (case insensitive) the dfdl:elementID property values of one of the element branches of the choice, and if so discriminates in favour of that branch. The parser then goes straight to that branch, ignoring schema order. Because the branch is 'known to exist' no backtracking takes place if a processing error subsequently occurs. Rules: - Both properties behave like dfdl:ref and dfdl:hiddenGroupRef in that it is not possible to set a value in scope by a dfdl:format annotation, and is only set at its point of use. This is because there is nothing sensible that could be set in scope **. Empty string is not an allowed value. - Both properties are only used when parsing. - When dfdl:choiceBranchRef is present, all choice branches must be local elements or element references. It is a schema definition error otherwise. - It is a processing error if the resolved value of dfdl:choiceBranchRef does not match one of the branches. - It is a schema definition error if individual dfdl:elementID values are not unique across all elements that are branches of an xs:choice that carries dfdl:choiceBranchRef. - It is not a schema definition error if both dfdl:initiatedContent and dfdl:choiceBranchRef, are provided on the same choice, nor if a discriminator exists on that choice branch. ++ ** Consequently adding support for the property to existing DFDL implementations will not suddenly cause errors to appear in existing DFDL schemas. ++ Reasoning. If a discriminator is evaluated and there is no point of uncertainty, it simply behaves like an assert, specifically if it fails it causes a processing error without backtracking. Use of dfdl:choiceBranchRef is just another way to get into this situation. (The property dfdl:initiatedContent may be rewritten as a series of discriminators on the child elements which test that the (initiated) element exists, hence same applies). 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 28/03/2012 16:32 ----- From: Steve Hanson/UK/IBM To: dfdl-wg(a)ogf.org Date: 27/03/2012 14:09 Subject: Fw: [DFDL-WG] Action 145: 'dispatch' way of discriminating a choice for better performance Hi Mike I agree. When I wrote the SWIFT example expression that I realised this was becoming a bit too complicated. IBM MRM has a quick way of dispatching a choice that uses a similar mechanism to the one you propose. It has an optional property called 'Message Alias'. The parser first tries to match the tag against the element name, and if that fails it tries the alias. I've modified my proposal accordingly. Regarding wildcards, the approach you show was what we had agreed upon a couple of years ago when we dropped wildcards. I would prefer not to add them back in for 1.0, but I have had some feedback from IBMers modeling envelope/payload formats that they want a loose-coupling approach as that fits better with other tools and is scalable. Let's treat this as a separate issue. I'll go back to the IBMers so that I fully understand their concerns, and if necessary I will bring back to the WG as a new agenda item. So all we need to ensure for now is that whatever mechanism we come up with is extensible to wildcards, if needed. Revised details: A new dfdl:element property is added called dfdl:elementAlias of type 'List of String'. This provides one or more alternative names for the element. Only allowed on local element and global element, not on element reference or simple type. A new dfdl:choice property is added called dfdl:choiceBranchRef of type DFDL Expression. The expression must evaluate to String. The string must match (case insensitive) either the element name or one of the dfdl:elementAlias property values of one of the element branches of the choice, and if so discriminates in favour of that branch. The parser then goes straight to that branch, ignoring schema order. Because the branch is 'known to exist' no backtracking takes place if a processing error occurs. Rules: - Both properties behave like dfdl:ref and dfdl:hiddenGroupRef in that it is not possible to set a value in scope by a dfdl:format annotation, and is only set at its point of use. This is because there is nothing sensible that could be set in scope. But it has the benefit that adding support for the property to existing DFDL implementations will not suddenly cause errors to appear in existing DFDL schemas. Empty string is not an allowed value. - Both properties are only used when parsing. - When dfdl:choiceBranchRef is preent, all choice branches must be local elements or element references. It is a schema definition error otherwise. - It is a processing error if the resolved xs:string value of dfdl:choiceBranchRef does not match one of the branches. - It is a schema definition error if a choice has both dfdl:choiceBranchRef set and dfdl:initiatedContent="yes". - It is a schema definition error if individual dfdl:elementAlias values are not unique a) across all elements that are branches of a given xs:choice and b) across all global elements in the schema. So we now have the ability to apply a simple lookup before we start to process a choice. That makes the processing time for each branch of the choice independent of its order in the schema. Questions: - What happens if we encounter a discriminator once we are processing the branch and its point of uncertainty is the choice ? 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 27/03/2012 13:41 ----- From: Mike Beckerle <mbeckerle.dfdl(a)gmail.com> To: Steve Hanson/UK/IBM@IBMGB Cc: dfdl-wg(a)ogf.org Date: 21/03/2012 15:57 Subject: Re: [DFDL-WG] Action 145: 'dispatch' way of discriminating a choice for better performance (updated) Sent by: dfdl-wg-bounces(a)ogf.org The whole point of this thing is to be faster, not more general, so my reaction is too much XPath expression complexity here. Consider this. If the tag is some 2-character code that does NOT want to be the same as the element names (for example because they're digits, so they can't be the element names exactly since element names have to begin with an alpha char. Digits also aren't useful from readability perspective as names), then you'll need a big lookup table in the choiceBranchRef expression that translates from the codes to the QNames. We don't have a case statement in the expression language, so you've just moved the big linear evaluation chain out of evaluating choice discriminators one after another and into a big if-then-else nest in the choiceBranchRef expression. I don't see a performance gain here. I suggest dropping the QName stuff, and requiring a dfdl:choiceID property on the elements that is an NCName. (Well, we might want those QName functions anyway in the expression language. But I wouldn't use them for this rapid choice dispatch feature. You could certainly use them in discriminators. ) The expression would then have to evaluate to a value that is matched against this choiceID. I suggest exact match, not respecting ignoreCase for example. That eliminates all the QName complexity and is amenable to high-speed compact lookup table implementation. I tend to think the element names want to be a little bit more descriptive than these tag values would want to be so using the element names as the tags feels undesirable to me. Particularly because we want the tags to be conveniently computed, for example by just grabbing a fixed-length string out of a data field. You end up with something like this: <element name="tag" type="string" dfdl:length="{ 2 }" ..../> <choice dfdl:choiceBranchRef="{ ../tag }"> <element name="someName" dfdl:choiceID="02" .../> <element name="anotherName" dfdl:choiceID="73" .../> .... </choice> As for the wild-card issue. I think we can finesse this. Consider this model: <element name="tag" type="string" dfdl:length="{ 2 }" ..../> <choice>  <choice dfdl:choiceBranchRef="{ ../tag }"> <element name="someName" dfdl:choiceID="02" .../> <element name="anotherName" dfdl:choiceID="73" .../> .... </choice>  <element name="extensionRecord"> <complexType> <sequence>  <element name="extensionType" type="string" dfdl:inputValueCalc="../../tag" .../> .... </sequence> </complexType> </element> </choice> The inner choice uses the fast dispatch. The outer choice lets me also have an alternative that absorbs a more general syntax to provide some way for a user to model their extensions to the choice set. The extensionType field captures the tag and stores it inside the extension record where it won't get disassociated. The user's "extensionRecord" would not be a special DFDL wildcard construct, just an element format they create which is general enough to parse their extensions. Or this extension could be predefined as part of a standard, to accept any standard-defined acceptable extension record a user might need so long as there is some set of rules all extension records must obey. Given this, do we really need special wildcard constructs? ...mikeb From: Steve Hanson <smh(a)uk.ibm.com> To: dfdl-wg(a)ogf.org, Date: 24.03.2012 02:27 Subject: [DFDL-WG] Action 145: 'dispatch' way of discriminating a choice for better performance The enveope/payload style of data format is quite common, where the envelope provides control information and the payload contains the business data. Examples are SWIFT and SAP IDocs. Typically the envelope contains a tag that identifies the payload, which can be one of many types. For SWIFT there are 300 possible types. To model this today in DFDL requires an xs:choice with each type modeled as an xs:element branch of the choice. A discriminator on each xs:element refers back to the envelope tag element thus enabling the choice to be resolved. There are two issues with this approach. 1) Performance. Even if the elements in the branches are ordered for expected frequency, there will still be cases when tens or hundreds of discriminators need to be evaluated before the choice is resolved. 2) Tight coupling. When a new type is added, a new element branch needs to be added to the choice. Action 145 proposes a mechanism to solve issue #1 and which opens the door to a possible extension to DFDL to solve issue #2 - namely a faster way to resolve a choice. Details: A new dfdl:choice property is added called dfdl:choiceBranchRef of type DFDL Expression. The expression must evaluate to a QName which corresponds to one of the element branches of the choice, and asserts 'known to exist' for that branch. Rules: - The property behaves like dfdl:ref and dfdl:hiddenGroupRef in that it is not possible to set a value in scope by a dfdl:format annotation, and is only set at its point of use. This is because there is nothing sensible that could be set in scope. But it has the benefit that adding support for the property to existing DFDL implementations will not suddenly cause errors to appear in existing DFDL schemas. - Empty string is not an allowed value. - The property is only used when parsing. - All branches must be local elements or element references. It is a schema definition error if any branch is a sequence, a choice or a group reference. - It is a processing error if the QName does not resolve to one of the branches when parsing.. - It is a schema definition error if a choice has the property set and also has dfdl:initiatedContent="yes" set locally. - Because the expression must return a QName, the expression language must provide a constructor for creating a QName from a namespace string and a name string. If you take SWIFT MT103 payload as an example, the tag in the envelope says "103" but a DFDL schema would actually model the global MT103 element with name "Document" and namespace ="urn:swift:xsd:fin.103.2011". So the dfdl:choiceBranchRef expression would have to look like: {fn:QName(fn:concat(fn:concat('urn:swift:xsd:fin.', FinMessage/Block2/MessageType), ".2011"), 'Document')} So we now have the ability to derive a QName and apply it before we start to process a choice. That makes the processing time for each branch of the choice independent of its order in the schema. We still have issue #2 so when a new payload is added, a new branch must be added to the choice. A solution to this is to allows xs:any wildcard elements back into DFDL, then provide a property dfdl:wildcardRef which works in the same way as dfdl:choiceRef. So at the point of encountering the wildcard we know its resolution in the schema. This obviously will require some further discussion, but you can see how this ability to evaluate an expression and return a QName can be used in multiple ways. 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 -- 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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Fw: Action 145: 'dispatch' way of discriminating a choice for better performance - example added
by Steve Hanson 10 Apr '12

10 Apr '12

Added an example as per action 145; <xs:complexType> <xs:sequence> <xs:element name="tag" type="xs:string" ../> .. <xs:choice dfdl:choiceBranchRef={../tag} ..> <xs:element name="order" dfdl:elementID="1" ../> <xs:element name="address" dfdl:elementID="2" ../> <xs:element ref="stock" /> </xs:choice> </xs:sequence> </xs:complexType> <xs:element name="stock" dfdl:elementID="3" ../> ------------------------------------------------------------------------------------------------------------------------------------- Updated to reflect the outcome of DFDL WG call on 5th April. Revised details: A new dfdl:element property is added called dfdl:elementID of type 'DFDL String Literal'. This provides a single alternative name for the element. Only allowed on local element and global element, not on element reference or simple type. A new dfdl:choice property is added called dfdl:choiceBranchRef of type 'DFDL Expression'. The expression must evaluate to a DFDL String Literal. The resultant string must match (case insensitive) the dfdl:elementID property values of one of the element branches of the choice, and if so discriminates in favour of that branch. The parser then goes straight to that branch, ignoring schema order. Because the branch is 'known to exist' no backtracking takes place if a processing error subsequently occurs. Rules: - Both properties behave like dfdl:ref and dfdl:hiddenGroupRef in that it is not possible to set a value in scope by a dfdl:format annotation, and is only set at its point of use. This is because there is nothing sensible that could be set in scope **. Empty string is not an allowed value. - Both properties are only used when parsing. - When dfdl:choiceBranchRef is present, all choice branches must be local elements or element references. It is a schema definition error otherwise. - It is a processing error if the resolved value of dfdl:choiceBranchRef does not match one of the branches. - It is a schema definition error if individual dfdl:elementID values are not unique across all elements that are branches of an xs:choice that carries dfdl:choiceBranchRef. - It is not a schema definition error if both dfdl:initiatedContent and dfdl:choiceBranchRef, are provided on the same choice, nor if a discriminator exists on that choice branch. ++ ** Consequently adding support for the property to existing DFDL implementations will not suddenly cause errors to appear in existing DFDL schemas. ++ Reasoning. If a discriminator is evaluated and there is no point of uncertainty, it simply behaves like an assert, specifically if it fails it causes a processing error without backtracking. Use of dfdl:choiceBranchRef is just another way to get into this situation. (The property dfdl:initiatedContent may be rewritten as a series of discriminators on the child elements which test that the (initiated) element exists, hence same applies). 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 28/03/2012 16:32 ----- From: Steve Hanson/UK/IBM To: dfdl-wg(a)ogf.org Date: 27/03/2012 14:09 Subject: Fw: [DFDL-WG] Action 145: 'dispatch' way of discriminating a choice for better performance Hi Mike I agree. When I wrote the SWIFT example expression that I realised this was becoming a bit too complicated. IBM MRM has a quick way of dispatching a choice that uses a similar mechanism to the one you propose. It has an optional property called 'Message Alias'. The parser first tries to match the tag against the element name, and if that fails it tries the alias. I've modified my proposal accordingly. Regarding wildcards, the approach you show was what we had agreed upon a couple of years ago when we dropped wildcards. I would prefer not to add them back in for 1.0, but I have had some feedback from IBMers modeling envelope/payload formats that they want a loose-coupling approach as that fits better with other tools and is scalable. Let's treat this as a separate issue. I'll go back to the IBMers so that I fully understand their concerns, and if necessary I will bring back to the WG as a new agenda item. So all we need to ensure for now is that whatever mechanism we come up with is extensible to wildcards, if needed. Revised details: A new dfdl:element property is added called dfdl:elementAlias of type 'List of String'. This provides one or more alternative names for the element. Only allowed on local element and global element, not on element reference or simple type. A new dfdl:choice property is added called dfdl:choiceBranchRef of type DFDL Expression. The expression must evaluate to String. The string must match (case insensitive) either the element name or one of the dfdl:elementAlias property values of one of the element branches of the choice, and if so discriminates in favour of that branch. The parser then goes straight to that branch, ignoring schema order. Because the branch is 'known to exist' no backtracking takes place if a processing error occurs. Rules: - Both properties behave like dfdl:ref and dfdl:hiddenGroupRef in that it is not possible to set a value in scope by a dfdl:format annotation, and is only set at its point of use. This is because there is nothing sensible that could be set in scope. But it has the benefit that adding support for the property to existing DFDL implementations will not suddenly cause errors to appear in existing DFDL schemas. Empty string is not an allowed value. - Both properties are only used when parsing. - When dfdl:choiceBranchRef is preent, all choice branches must be local elements or element references. It is a schema definition error otherwise. - It is a processing error if the resolved xs:string value of dfdl:choiceBranchRef does not match one of the branches. - It is a schema definition error if a choice has both dfdl:choiceBranchRef set and dfdl:initiatedContent="yes". - It is a schema definition error if individual dfdl:elementAlias values are not unique a) across all elements that are branches of a given xs:choice and b) across all global elements in the schema. So we now have the ability to apply a simple lookup before we start to process a choice. That makes the processing time for each branch of the choice independent of its order in the schema. Questions: - What happens if we encounter a discriminator once we are processing the branch and its point of uncertainty is the choice ? 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 27/03/2012 13:41 ----- From: Mike Beckerle <mbeckerle.dfdl(a)gmail.com> To: Steve Hanson/UK/IBM@IBMGB Cc: dfdl-wg(a)ogf.org Date: 21/03/2012 15:57 Subject: Re: [DFDL-WG] Action 145: 'dispatch' way of discriminating a choice for better performance (updated) Sent by: dfdl-wg-bounces(a)ogf.org The whole point of this thing is to be faster, not more general, so my reaction is too much XPath expression complexity here. Consider this. If the tag is some 2-character code that does NOT want to be the same as the element names (for example because they're digits, so they can't be the element names exactly since element names have to begin with an alpha char. Digits also aren't useful from readability perspective as names), then you'll need a big lookup table in the choiceBranchRef expression that translates from the codes to the QNames. We don't have a case statement in the expression language, so you've just moved the big linear evaluation chain out of evaluating choice discriminators one after another and into a big if-then-else nest in the choiceBranchRef expression. I don't see a performance gain here. I suggest dropping the QName stuff, and requiring a dfdl:choiceID property on the elements that is an NCName. (Well, we might want those QName functions anyway in the expression language. But I wouldn't use them for this rapid choice dispatch feature. You could certainly use them in discriminators. ) The expression would then have to evaluate to a value that is matched against this choiceID. I suggest exact match, not respecting ignoreCase for example. That eliminates all the QName complexity and is amenable to high-speed compact lookup table implementation. I tend to think the element names want to be a little bit more descriptive than these tag values would want to be so using the element names as the tags feels undesirable to me. Particularly because we want the tags to be conveniently computed, for example by just grabbing a fixed-length string out of a data field. You end up with something like this: <element name="tag" type="string" dfdl:length="{ 2 }" ..../> <choice dfdl:choiceBranchRef="{ ../tag }"> <element name="someName" dfdl:choiceID="02" .../> <element name="anotherName" dfdl:choiceID="73" .../> .... </choice> As for the wild-card issue. I think we can finesse this. Consider this model: <element name="tag" type="string" dfdl:length="{ 2 }" ..../> <choice>  <choice dfdl:choiceBranchRef="{ ../tag }"> <element name="someName" dfdl:choiceID="02" .../> <element name="anotherName" dfdl:choiceID="73" .../> .... </choice>  <element name="extensionRecord"> <complexType> <sequence>  <element name="extensionType" type="string" dfdl:inputValueCalc="../../tag" .../> .... </sequence> </complexType> </element> </choice> The inner choice uses the fast dispatch. The outer choice lets me also have an alternative that absorbs a more general syntax to provide some way for a user to model their extensions to the choice set. The extensionType field captures the tag and stores it inside the extension record where it won't get disassociated. The user's "extensionRecord" would not be a special DFDL wildcard construct, just an element format they create which is general enough to parse their extensions. Or this extension could be predefined as part of a standard, to accept any standard-defined acceptable extension record a user might need so long as there is some set of rules all extension records must obey. Given this, do we really need special wildcard constructs? ...mikeb From: Steve Hanson <smh(a)uk.ibm.com> To: dfdl-wg(a)ogf.org, Date: 24.03.2012 02:27 Subject: [DFDL-WG] Action 145: 'dispatch' way of discriminating a choice for better performance The enveope/payload style of data format is quite common, where the envelope provides control information and the payload contains the business data. Examples are SWIFT and SAP IDocs. Typically the envelope contains a tag that identifies the payload, which can be one of many types. For SWIFT there are 300 possible types. To model this today in DFDL requires an xs:choice with each type modeled as an xs:element branch of the choice. A discriminator on each xs:element refers back to the envelope tag element thus enabling the choice to be resolved. There are two issues with this approach. 1) Performance. Even if the elements in the branches are ordered for expected frequency, there will still be cases when tens or hundreds of discriminators need to be evaluated before the choice is resolved. 2) Tight coupling. When a new type is added, a new element branch needs to be added to the choice. Action 145 proposes a mechanism to solve issue #1 and which opens the door to a possible extension to DFDL to solve issue #2 - namely a faster way to resolve a choice. Details: A new dfdl:choice property is added called dfdl:choiceBranchRef of type DFDL Expression. The expression must evaluate to a QName which corresponds to one of the element branches of the choice, and asserts 'known to exist' for that branch. Rules: - The property behaves like dfdl:ref and dfdl:hiddenGroupRef in that it is not possible to set a value in scope by a dfdl:format annotation, and is only set at its point of use. This is because there is nothing sensible that could be set in scope. But it has the benefit that adding support for the property to existing DFDL implementations will not suddenly cause errors to appear in existing DFDL schemas. - Empty string is not an allowed value. - The property is only used when parsing. - All branches must be local elements or element references. It is a schema definition error if any branch is a sequence, a choice or a group reference. - It is a processing error if the QName does not resolve to one of the branches when parsing.. - It is a schema definition error if a choice has the property set and also has dfdl:initiatedContent="yes" set locally. - Because the expression must return a QName, the expression language must provide a constructor for creating a QName from a namespace string and a name string. If you take SWIFT MT103 payload as an example, the tag in the envelope says "103" but a DFDL schema would actually model the global MT103 element with name "Document" and namespace ="urn:swift:xsd:fin.103.2011". So the dfdl:choiceBranchRef expression would have to look like: {fn:QName(fn:concat(fn:concat('urn:swift:xsd:fin.', FinMessage/Block2/MessageType), ".2011"), 'Document')} So we now have the ability to derive a QName and apply it before we start to process a choice. That makes the processing time for each branch of the choice independent of its order in the schema. We still have issue #2 so when a new payload is added, a new branch must be added to the choice. A solution to this is to allows xs:any wildcard elements back into DFDL, then provide a property dfdl:wildcardRef which works in the same way as dfdl:choiceRef. So at the point of encountering the wildcard we know its resolution in the schema. This obviously will require some further discussion, but you can see how this ability to evaluate an expression and return a QName can be used in multiple ways. 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 -- 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 2012-04-10
by Steve Hanson 10 Apr '12

10 Apr '12

Please find agenda attached for the above call on GridForge at https://forge.ogf.org/sf/docman/do/downloadDocument/projects.dfdl-wg/docman… 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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checking on 'no recursion' restriction - are we sure we can live without it
by Mike Beckerle 09 Apr '12

09 Apr '12

DFDL v1.0 spec currently disallows recursive types. Are we sure we can live without this? Seems to me there are many formats e.g., JSON, which are popular now, and which naturally require recursion to express. There are a number of document-like formats - there's a fuzzy grey area where documents and data records overlap, and these will naturally be modeled using recursion. Even formats like EDIFACT allow segment nesting, though I'm not sure about whether recursive definitions are allowed or precluded, a generic EDIFACT parser wouldn't know any specific segment types, and would want to have a recursively defined generic segment structure. Comments? ...mikeb -- Mike Beckerle | OGF DFDL WG Co-Chair Tel: 781-330-0412

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DFDL based application released
by Michele Zundo 06 Apr '12

06 Apr '12

Dear all, you might be interested to know that yesterday we have freely released an application for visualizing binary satellite data (compliant to CCSDS standard) which based on DFDL. The satellite data binary structure for a number of ESA Earth Observation Mission has been described using DFDL schemas and a java parser implemented which allow the application to access all different data fields. The binary DFDL schemas can be also edited by the user to describe custom type of satellite data (i.e. changing the structure) without changing the application. We are considering in future to release the java Read API stand alone for everybody to use and build their own applications. The release message with pointers to URL to download the application is attached here below: ***** Dear all, please be informed today we have released the (Space-to-Ground) S2G Data Viewer which can be freely downloaded from : http://eop-cfi.esa.int/S2G/s2g.html S2G data Viewer is a modern, multi platform, extendable application to inspect CCSDS data (CADU, TF/VCDU and SP) and example screenshot attached below. The application is currently configured to support the following ESA Earth Observation Mission (including the custom Source Packet Data Header): Sentinel-1 Sentinel-2 Sentinel-3 Swarm EarthCARE and it can be extended by the user to support different type of data or new missions. I invite you to download and use it to support your AIV activities and, if necessary, to send any feedback to s2g(a)eopp.esa.int ****** ----------------------------------------- Mr. Michele Zundo Head of Ground System Definition and Verification Office EOP-PEP European Space Agency, ESTEC e-mail: michele.zundo(a)esa.int This message and any attachments are intended for the use of the addressee or addressees only. The unauthorised disclosure, use, dissemination or copying (either in whole or in part) of its content is not permitted. If you received this message in error, please notify the sender and delete it from your system. Emails can be altered and their integrity cannot be guaranteed by the sender. Please consider the environment before printing this email.

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OGF DFDL WG Call Minutes 2012-04-05
by Steve Hanson 05 Apr '12

05 Apr '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 still at version 8 and may be found via https://forge.ogf.org/sf/projects/dfdl-wg 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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Re: [DFDL-WG] Issue 168 - Re: Fw: Escape scheme properties that can be expressions
by Steve Hanson 05 Apr '12

05 Apr '12

Agreed on DFDL WG call on 5th April 2012 to take an errata to improve the wording as below, but not to disallow relative exprs in defineFormat or defineEscapeScheme, as it prejudges usage. 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: Mike Beckerle <mbeckerle.dfdl(a)gmail.com> Cc: dfdl-wg(a)ogf.org Date: 05/04/2012 12:40 Subject: Re: Issue 168 - Re: [DFDL-WG] Fw: Escape scheme properties that can be expressions Mike I think the wording in 6.3.2 applies specifically to the anonymous dfdl:format. I don't think it was intended to apply to dfdl:format inside dfdl:defineFormat nor to dfdl:escapeScheme inside dfdl:defineEscapeScheme, presumably due to the reasons we discussed on last week's call - namely that by using dfdl:ref they can be applied directly to a specific object. Of course, dfdl:ref can be used on the anonymous dfdl:format too, So the 6.3.2 words should have said: "In the dfd:format annotation on the xs:schema, a DFDL property either declared locally or obtained via dfdl:ref and which uses a DFDL expressions to provide its value MAY NOT contain relative paths". So I think we still need to decide on dfdl:format inside dfdl:defineFormat nor to dfdl:escapeScheme inside dfdl:defineEscapeScheme. 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: Mike Beckerle <mbeckerle.dfdl(a)gmail.com> To: Steve Hanson/UK/IBM@IBMGB Cc: dfdl-wg(a)ogf.org Date: 03/04/2012 15:45 Subject: Issue 168 - Re: [DFDL-WG] Fw: Escape scheme properties that can be expressions In the absence of a compelling reason to allow relative paths here, I think the conservative choice is to retain this rule from 6.3.2. However, I did think about this and my evaluation on this topic is that allowing relative paths makes things just a little more complicated analytically to insure one gets good performance, but as DFDL does not allow recursive types, it is a relatively simple analysis to convert any relative path use in DFDL into absolute paths. So I am not worried about there being performance impact. ...mikeb On Mon, Apr 2, 2012 at 7:30 AM, Steve Hanson <smh(a)uk.ibm.com> wrote: We took action 168 on the last call to discuss the issue of relative paths in expressions for properties in global formats. 168 Relative path expressions in global annotations (Mike) 28/03: Mike to check that allowing relative paths does not cause performance problems for an implementation. 05/04: Just seen this in section 6.3.2. of the spec: "DFDL expressions that are used to provide the value of DFDL properties in the dfd:format annotation on the xs:schema MAY NOT contain relative paths". 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 02/04/2012 12:28 ----- From: Steve Hanson/UK/IBM To: dfdl-wg(a)ogf.org Date: 14/03/2012 16:09 Subject: Escape scheme properties that can be expressions The spec allows the escapeCharacter and escapeEscapeCharacter of DFDL escapeScheme to be expressions, in case the characters are supplied dynamically in the data stream. However given that escape schemes are defined globally, should these properties be permitted to take relative paths in the expression? Today the spec implicitly allows this, meaning an implementation can not entirely validate an escapeScheme annotation up front, but must validate escapeCharacter and escapeEscapeCharacter at each point of use. I'm not sure it makes much sense for the path to be anything than absolute. 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 -- Mike Beckerle | OGF DFDL WG Co-Chair Tel: 781-330-0412 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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Re: [DFDL-WG] Fw: Action 167: textNumberPatterns with P, V, # - allowable combinations
by Steve Hanson 05 Apr '12

05 Apr '12

Agreed on DFDL WG call 5th April 2012: A pattern with a V symbol must not have # symbols to the right of the V symbol. A pattern with P symbols at the left end must have no # symbols in the pattern. A pattern with P symbols at the right end has no restrictions. ICU padding and DFDL padding/trimming are independent mechanisms, may be used in conjunction. When ICU padding is used in pattern (* symbol) it is a schema definition error if P or V symbol in pattern. When ICU significant digits in pattern (@ symbol) it is a schema definition error if P or V symbol in pattern. 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 Cc: Richard Schofield/UK/IBM@IBMGB Date: 22/03/2012 11:01 Subject: Fw: Action 167: textNumberPatterns with P,V, # - allowable combinations Further to discussion on the call, here is what IBM COBOL manual says about PIC P. An assumed decimal scaling position. It is used to specify the location of an assumed decimal point when the point is not within the number that appears in the data item. The scaling position character P is not counted in the size of the data item. Scaling position characters are counted in determining the maximum number of digit positions (63) in numeric-edited items or in items that appear as arithmetic operands. The scaling position character P may appear only as a continuous string of Ps in the leftmost or rightmost digit positions within a PICTURE character-string. Because the scaling position character P implies an assumed decimal point (to the left of the Ps, if the Ps are leftmost PICTURE characters; to the right of the Ps, if the Ps are rightmost PICTURE characters), the assumed decimal point symbol, V, is redundant as either the leftmost or rightmost character within such a PICTURE description. In certain operations that reference a data item whose PICTURE character-string contains the symbol P, the algebraic value of the data item is used rather than the actual character representation of the data item. This algebraic value assumes the decimal point in the prescribed location and zero in place of the digit position specified by the symbol P. The size of the value is the number of digit positions represented by the PICTURE character-string. These operations are any of the following: Any operation requiring a numeric sending operand. A MOVE statement where the sending operand is numeric and its PICTURE character-string contains the symbol P. A MOVE statement where the sending operand is numeric-edited and its PICTURE character-string contains the symbol P and the receiving operand is numeric or numeric-edited. A comparison operation where both operands are numeric. In all other operations the digit positions specified with the symbol P are ignored and are not counted in the size of the operand. This implies that the scaling should be applied as a lexical operation on the data. In other words two COBOL fields, one with PIC PP9 and value '2' and one with PP999 and value '002' do not result in the same logical number. There is an equivalence between V and P. PP999 == V99999 and 999PP == 99999V == 99999. If we consider things in these terms the reasoning is simpler. To prevent # symbol zero suppression from changing the value, rule a) must apply and there must be no # to the right of the V. That restates our rules as: a) A pattern with a V symbol must not have # symbols to the right of the V symbol. b) A pattern with P symbols at the left end must have no # symbols in the pattern. c) A pattern with P symbols at the right end has no restrictions. There is another problem though. The number can be trimmed using the pad character from either or both ends depending on justification, before applying the number pattern. If the pad character is 0 then this can also cause 0's to be lost and result in mis-application of V and P symbols. I'm not sure there is much we can do about this. Modelers need to be careful when padding/trimming that they get the justification correct. For example, we typically think of numbers as being right justified, but for a number with Ps on the left, it is effectively left justified and should be modeled as such. We added errata 2.25 which prevented trimming from leaving an empty string. I am thinking that this errata should actually say that trimming must leave at least the minimum number of digits implied by the pattern, as an extra safeguard? We mustn't disallow trimming/padding altogether as it is used to remove spaces. The ICU pad character symbol * is used to provide a pad character when the data is shorter than the pattern. This is only used to pad when unparsing, it is not used to trim. But it might be safer to disallow P and V symbols when * is used? Reading the ICU description of significant digit symbol @, explicit decimal points are disallowed. I think we should disallow P and V symbols when @ symbol is used. Errata 2.28 should be updated. 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 22/03/2012 09:22 ----- From: Steve Hanson/UK/IBM To: dfdl-wg(a)ogf.org Date: 21/03/2012 10:34 Subject: Action 167: textNumberPatterns with P,V, # - allowable combinations Last week we agreed that disallowing text number patterns that contained a # symbol and either a P or V symbol was too restrictive. Accordingly the following rules are proposed to control when # may be used in the same pattern as P or V to ensure an unambiguous pattern. a) Pattern must not have # symbols to the right of the V symbol. b) If pattern has P symbols at the left end, then there must be as many 0 symbols adjacent to the rightmost P symbol as there are P symbols. c) If pattern has P symbols at the right end, there are no restrictions. If a) or b) are violated it is a schema definition error. 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 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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Issue 145 - cobol 88 example with multiple definitions per 88
by Mike Beckerle 05 Apr '12

05 Apr '12

Cobol below illustrates how the 88 statement can define more than one constant to represent a selection. E.g., the definition for Consonant below. A single "Accept Char....When Consonant" test tests the char value against the entire specification including individual enums, and the ranges specified as well. This is the mechanism I've seen used to specify that several different enumerated codes correspond to the same record format. I've only seen the multiple enumerated constants in practice, not the range specifications: IDENTIFICATION DIVISION. PROGRAM-ID. Conditions. AUTHOR. Michael Coughlan. * An example program demonstrating the use of * condition names (level 88's). * The EVALUATE and PERFORM verbs are also used. DATA DIVISION. WORKING-STORAGE SECTION. 01 Char PIC X. 88 Vowel VALUE "a", "e", "i", "o", "u". 88 Consonant VALUE "b", "c", "d", "f", "g", "h" "j" THRU "n", "p" THRU "t", "v" THRU "z". 88 Digit VALUE "0" THRU "9". 88 ValidCharacter VALUE "a" THRU "z", "0" THRU "9". PROCEDURE DIVISION. Begin. DISPLAY "Enter lower case character or digit. No data ends.". ACCEPT Char. PERFORM UNTIL NOT ValidCharacter EVALUATE TRUE WHEN Vowel DISPLAY "The letter " Char " is a vowel." WHEN Consonant DISPLAY "The letter " Char " is a consonant." WHEN Digit DISPLAY Char " is a digit." WHEN OTHER DISPLAY "problems found" END-EVALUATE END-PERFORM STOP RUN. I suggest that tests as complicated as the ones above that include range specifications should turn into normal discriminators in DFDL. But what if it was just enumerated values, e.g., I take the ranges off.... 01 Char PIC XX. 88 BaseRecord VALUE "a1", "11", "52". 88 Ext-Record VALUE "bb", "b0" This is the example I've actually seen in data. So in this case we just need the ability for the elementAlias to be a list of potential values. Or we can just be satisfied with requiring each of a1, 11, and 52 to be a separate element with a different name, so the above becomes a choice of 6 things, or we can just require a regular old discriminator in any case more general than single-value dispatch. I wanted everyone to see the example, but I actually advocate the narrowest possible definition here. I think the dfdl:elementAlias should be exactly one value only, and users should use a discriminator with a test for anything more general. ...mikeb

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issue 145 - name dfdl:elementAlias
by Mike Beckerle 05 Apr '12

05 Apr '12

About the name dfdl:elementAlias It suggests that this is another element name, and in other contexts than a choice it might be used as well, and in addition it suggests that the dfdl:choiceBranchRef can evaluate to the element name, or to this alias. I think the definition of all this behavior should be narrower, and the names should suggest this. dfdl:choiceBranchRef dfdl:choiceBranchID seem like the right pairing. A choice branch ref can refer to exactly and only the choice branch ID, never the element name, and this ID is used only for choice branch ref purposes. ...mikeb -- Mike Beckerle | OGF DFDL WG Co-Chair Tel: 781-330-0412

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