April 2006 - dfdl-wg - lists.ogf.org

Meeting notes 2006-4-19
by Westhead, Martin (Martin) 09 May '06

09 May '06

It was a very short meeting this week... Present Bob McGrath Geoff Judd Steve Hanson Martin Westhead Notes - Document expected from Bob and Mike on arrays. o Bob gave an overview of this material - Martin reported that Tom Sugden now has some time and will be working on implementing a prototype of the conversion material

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Telcon today
by Westhead, Martin (Martin) 26 Apr '06

26 Apr '06

I'm afraid I will be unable to attend this week...sorry. Conference call instructions: Number: 1-800-664-0771 At the automated answering system, press 0 for the operator. Ask for the "Daffodil working group" call.

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Telcon today
by Westhead, Martin (Martin) 19 Apr '06

19 Apr '06

Conference call instructions: Number: 1-800-664-0771 At the automated answering system, press 0 for the operator. Ask for the "Daffodil working group" call. Web Conference: https://webconferencing.avaya.com <https://webconferencing.avaya.com/> Web Conference: Part. Code 785343; WebConf Reference 158672

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Telcon today
by Westhead, Martin (Martin) 17 Apr '06

17 Apr '06

Sorry for the late reminder. I'm afraid I will be unable to attend this week. Agenda items: - issue of defaults - arrays discussion - outstanding property document discussion Conference call instructions: Number: 1-800-664-0771 At the automated answering system, press 0 for the operator. Ask for the "Daffodil working group" call. Web Conference: https://webconferencing.avaya.com <https://webconferencing.avaya.com/> Web Conference: Part. Code 785343; WebConf Reference 158672

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RE: [dfdl-wg] string vs. hexBinary vs. opaque
by Westhead, Martin (Martin) 12 Apr '06

12 Apr '06

I like this Mike, I think its very useful. _____ From: owner-dfdl-wg(a)ggf.org [mailto:owner-dfdl-wg@ggf.org] On Behalf Of Mike Beckerle Sent: Wednesday, April 12, 2006 1:01 PM To: dfdl-wg(a)ggf.org Subject: [dfdl-wg] string vs. hexBinary vs. opaque I did some thinking on this topic. At least some IBMers thought this was coherent.

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RE: [dfdl-wg] How to deal with variable length elements?
by Westhead, Martin (Martin) 12 Apr '06

12 Apr '06

Hi Mike, I still don't quite understand could you put it in the context of a more complete example? Thanks, Martin _____ From: owner-dfdl-wg(a)ggf.org [mailto:owner-dfdl-wg@ggf.org] On Behalf Of Mike Beckerle Sent: Wednesday, April 12, 2006 12:16 PM To: Westhead, Martin (Martin) Cc: dfdl-wg(a)ggf.org; Robert E. McGrath; owner-dfdl-wg(a)ggf.org Subject: RE: [dfdl-wg] How to deal with variable length elements? The reason for the special @dfdl:index is because of the Xpath rules that position() is always inside the current context expression containing the call to position(). We need to index another structure with our index position. Can't do this in straight Xpath. If we add a "Let x = position() in ..." construct (Xquery has this), then we wouldn't need the @dfdl:index. ...mikeb Mike Beckerle STSM, Architect, Scalable Computing IBM Software Group Information Integration Solutions Westborough, MA 01581 voice and FAX 508-599-7148 home/mobile office 508-915-4795 "Westhead, Martin (Martin)" <westhead(a)avaya.com> Sent by: owner-dfdl-wg(a)ggf.org 04/05/2006 10:26 AM To Mike Beckerle/Worcester/IBM@IBMUS, "Robert E. McGrath" <mcgrath(a)ncsa.uiuc.edu> cc <dfdl-wg(a)ggf.org> Subject RE: [dfdl-wg] How to deal with variable length elements? Hi, This looks fine to me (modulo old syntax) except I don't understand the need to introduce this construct: "@dfdl:index". I guess in today's terms we might thing of this as a value in the context. However, I claim that we don't need it. I think we can achieve the same effect with the XPath function position(). position() should tell you where you are in the current sequence. If you want to know where you are in the parent sequence you can use ../position(). If your index starts from 0 use position()-1. If you store two elements in your sequence for every index (e.g. flat array of x-y coordinates) use position()/2. What does @dfdl:index do that you don't get out of position()? Cheers, Martin _____ From: owner-dfdl-wg(a)ggf.org [mailto:owner-dfdl-wg@ggf.org] On Behalf Of Mike Beckerle Sent: Friday, March 17, 2006 2:14 PM To: Robert E. McGrath Cc: dfdl-wg(a)ggf.org; owner-dfdl-wg(a)ggf.org Subject: Re: [dfdl-wg] How to deal with variable length elements? Hmmm. I think layered value calculation formulas which allow for a magic "myIndex" variable are perhaps an important device to make this class of layering possible.This makes the iteration over the elements implicit. I have one example which is the one where there is a vector of strings where the lengths of all the strings are stored first, separately from all the character data. A formula involving "myIndex" is used to glue the two pieces together. Here's the example as per our prototype from last summer: ...mikeb "Robert E. McGrath" <mcgrath(a)ncsa.uiuc.edu> Sent by: owner-dfdl-wg(a)ggf.org 03/17/2006 10:54 AM To dfdl-wg(a)ggf.org cc Subject Re: [dfdl-wg] How to deal with variable length elements? Following up on my email on ealier this week: I think there was a major flaw in what I wrote, and it is quite an "interesting" challenge. Let me review: I am thinking about how to describe reading data into a 1D array. Steve provided a markup for the XML element. The challenge I'm looking at is that the data need not be a image of the memory layout. To give one example, a very sparse array might be stored as a series of (index, value) pairs for the non-empty places, all others implied to be zero or fill or whatever. The goal is to have the XML array be fully populated from this sparse form--or whatever layout--on disk. (Please assume for now that this is a reasonable goal!) The XML and DFDL will tell us the data type, and presumably we know the extent of the data on disk. But we need to decode the storage to generate all the elements values and fills. In my earlier email, I offered a description that included an 'Iterator' conversion. I now think this is inadequate. In fact you need two cooperating 'Iterators'! Ick! Here is my revised pipeline. Data is read from bottom to top. I sketch what each conversion is tasked to do. I think the 'Decoder' needs to know info from both the 'Iterator' (it asks for each element in the order it wants them) and 'Float' (it tells the size of the 'value' to get). == <<XML element with multiple occurs: 1D array >> ^ | Iterator conversion: relevant props: minOccurs="0" maxOccurs="<<setting>>, et al Get 'maxOccurs' elements of type datatype. ^ | Float conversion: relevant props: data description of element Decode bytes ^ | Decoder conversion: produces the bytes 'nth' _value_ in the array. Input: what position is needed. may need separators and other props: depends on encoding Output: sizeof datatype bytes, the _value_ Side effect: after whole array is read, consumes all the storage. Difficult to characterize the intermediate state. ^ | Data: read as bytes

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RE: [dfdl-wg] How to deal with variable length elements?
by Westhead, Martin (Martin) 12 Apr '06

12 Apr '06

Hi, This looks fine to me (modulo old syntax) except I don't understand the need to introduce this construct: "@dfdl:index". I guess in today's terms we might thing of this as a value in the context. However, I claim that we don't need it. I think we can achieve the same effect with the XPath function position(). position() should tell you where you are in the current sequence. If you want to know where you are in the parent sequence you can use ../position(). If your index starts from 0 use position()-1. If you store two elements in your sequence for every index (e.g. flat array of x-y coordinates) use position()/2. What does @dfdl:index do that you don't get out of position()? Cheers, Martin _____ From: owner-dfdl-wg(a)ggf.org [mailto:owner-dfdl-wg@ggf.org] On Behalf Of Mike Beckerle Sent: Friday, March 17, 2006 2:14 PM To: Robert E. McGrath Cc: dfdl-wg(a)ggf.org; owner-dfdl-wg(a)ggf.org Subject: Re: [dfdl-wg] How to deal with variable length elements? Hmmm. I think layered value calculation formulas which allow for a magic "myIndex" variable are perhaps an important device to make this class of layering possible.This makes the iteration over the elements implicit. I have one example which is the one where there is a vector of strings where the lengths of all the strings are stored first, separately from all the character data. A formula involving "myIndex" is used to glue the two pieces together. Here's the example as per our prototype from last summer: ...mikeb "Robert E. McGrath" <mcgrath(a)ncsa.uiuc.edu> Sent by: owner-dfdl-wg(a)ggf.org 03/17/2006 10:54 AM To dfdl-wg(a)ggf.org cc Subject Re: [dfdl-wg] How to deal with variable length elements? Following up on my email on ealier this week: I think there was a major flaw in what I wrote, and it is quite an "interesting" challenge. Let me review: I am thinking about how to describe reading data into a 1D array. Steve provided a markup for the XML element. The challenge I'm looking at is that the data need not be a image of the memory layout. To give one example, a very sparse array might be stored as a series of (index, value) pairs for the non-empty places, all others implied to be zero or fill or whatever. The goal is to have the XML array be fully populated from this sparse form--or whatever layout--on disk. (Please assume for now that this is a reasonable goal!) The XML and DFDL will tell us the data type, and presumably we know the extent of the data on disk. But we need to decode the storage to generate all the elements values and fills. In my earlier email, I offered a description that included an 'Iterator' conversion. I now think this is inadequate. In fact you need two cooperating 'Iterators'! Ick! Here is my revised pipeline. Data is read from bottom to top. I sketch what each conversion is tasked to do. I think the 'Decoder' needs to know info from both the 'Iterator' (it asks for each element in the order it wants them) and 'Float' (it tells the size of the 'value' to get). == <<XML element with multiple occurs: 1D array >> ^ | Iterator conversion: relevant props: minOccurs="0" maxOccurs="<<setting>>, et al Get 'maxOccurs' elements of type datatype. ^ | Float conversion: relevant props: data description of element Decode bytes ^ | Decoder conversion: produces the bytes 'nth' _value_ in the array. Input: what position is needed. may need separators and other props: depends on encoding Output: sizeof datatype bytes, the _value_ Side effect: after whole array is read, consumes all the storage. Difficult to characterize the intermediate state. ^ | Data: read as bytes

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Notes from Telcon 2006-04-06
by Westhead, Martin (Martin) 05 Apr '06

05 Apr '06

Present Martin Westhead Tara Talbott Mike Beckerle Steven Hanson Geoff Judd Properties document Some things that came out of the discussion (mainly from Mike who took better notes than me) - clarification on Opaque vs. binary (details below) - Generally the naming scheme looks ok, even the very long names like "syntaxFinalSeparatorCanBeMissing" are ok. - Adding a conceptual UML taxonomy of the various represetnation kinds would help to motivate the naming conventions used for the properties. - Want to break up big enums like repType and make them extensible. So that a library can add values to it. - Proposal: repType is a QName, not an enum, and a DFDL processor adds libraries that register the valid strings for it as part of their definitions. This allows refactoring the properties list into libraries. - Issues with library fragmentation: how small a subset of the libraries can you have and still call it DFDL? Discussion: not too small because you won't get interoperability. However, one can have data that uses only a subset of DFDL features, and then you can have software that only implements what you need. Your data and schemas will be DFDL conformant in that anyone with a conforming DFDL implementation will be able to read your data. However, you will not have software that can process data you receive from others which uses more features. This is an ok situation: conforming data and schemas, but subset implementation. - It would be good to be able to formally describe the subset of DFDL constructs that a subset implementation provides. E.g., an XML file which characterizes the subset formally. - Action for all to look at the paragraph in Steve's email about default values. Binary/Opaque issue: >From last week's notes: 1. Keep the group Binary. It covers situations where a binary representation in the logical model is either what we really want or is simply the best we can do. 2. Add the reptype 'text' to the group Binary. This is to cover text representations of binary data. i.e. we want to interpret the bytes on the disk as a text representation of binary data. [Question: what if the representation is base64 but we would like the logical model to represent it as xs:hexBinary? What if it is uuencoded?] 3. Add a new Group called Opaque. This would have the logical type xs:any and the representations 'text' or 'binaryStream'. A text representation means that this is an opaque string and it should be included in the logical model as CDATA. A binary representation means that it is an opaque Blob and it should be included in the logical model using a binary representation. We can choose any binary representation let us say hexBinary. Clarifications: an element of type hexBinary or base64Binary would behave, at an API level as both a string (can deliver hex characters in the case of hexBinary) and as a vector of bytes. An element of type Opaque would have no operations at an API level other than copy(), and size(). Could also add as a representation kind for binary data: uuencode, base100Binary, in addition to base64 and hex. Items for next week - issue of defaults - arrays discussion - outstanding property document discussion items

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Telcon tomorrow
by Westhead, Martin (Martin) 04 Apr '06

04 Apr '06

Preliminary Agenda 1. Continue last weeks discussion on Steve's document on Properties. In particular consider the Opaque/Binary data proposal from last week's notes. 2. Arrays - comments on length calculation in recent email from Mike. Conference call instructions: Number: 1-800-664-0771 At the automated answering system, press 0 for the operator. Ask for the "Daffodil working group" call. Web Conference: https://webconferencing.avaya.com <https://webconferencing.avaya.com/> Web Conference: Part. Code 785343; WebConf Reference 158672

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