[DFDL-WG] Variable occurrence of variable/fields
Steve Hanson
smh at uk.ibm.com
Tue Jul 26 07:52:49 CDT 2011
Hello Michele
Thank you for your interest in DFDL.
DFDL is able to describe a binary format with variable numbers of elements
where the count is provided earlier in the data, like you describe below.
Use dfdl:occursCountKind="expression" and set dfdl:occursCount to an XPath
expression that refers to the count field. (Ryan's format does not contain
a count, rather it contains a 'last item' indicator in the repeating data
itself, which is more tricky to model).
DFDL is able to model bit oriented data. Use dfdl:lengthUnits= "bits" and
dfdl:alignmentUnits="bits".
Are you a colleague of Dario Romano? We were contacted last year by Dario
who provided us with some sample satellite bit data that he wanted DFDL to
model. We used it as a proof point for the bit support in DFDL, and as a
result we changed the behaviour of dfdl:leadingSkip and dfdl:trailingSkip
to obey dfdl:alignmentUnits="bits".
Regards
Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
From:
Michele Zundo <michele.zundo at esa.int>
To:
dfdl-wg at ogf.org
Date:
26/07/2011 12:45
Subject:
[DFDL-WG] Variable occurrence of variable/fields
Sent by:
dfdl-wg-bounces at ogf.org
Dear all,
my 2 cents on variable occurrence fields.
We have been using XML syntax (in now defunct BinX format) to
describe the structure of ESA Earth Observation SMOS Mission Science
binary
data Product. (see http://www.smos.com.pt/)
We also developed some custom C/C++ library to allow Read/Write access to
these binary data as we felt this would allow to easily modify the binary
structure
of the data product without requiring application code changes but only
XML "schema".
One of the major limitation we have found in BinX (which I'm not sure has
been solved in DFDL)
is indeed related to describing a binary structure with variable number of
records where the number
is described (dynamically) within the binary itself. We had to define a
pre-processor of the binary data
which would read each instance of the file find out how many of the
records we had and create
at run-time a XML schema with the correct number of replication of the XML
code describing each
of the records. This is very inconvenient and un-elegant.
For example a binary data Product with a variable number of scientific
observation
would be (symbolically) structured as:
Number_of_Records
Data_Record_1 (blah, blah, etc etc )
Data_Record_2 ((blah, blah, etc etc)
.....
Record_N (with N= Number_of_Records )
It would be desirable to be able to specify such a data product like:
Number_of_Records
List (count=Number_of_Records) of Data_Record
The other feature which we greatly missed is bit level operation since
many of our Space data structure
are formatted at bit level e.g. 3 bits field + 2 bit field + 11 bit field
etc.
Regards
From: Ryan Farrell <ryan.farrell.ctr at nrl.navy.mil>
Date: July 19, 2011 20:12:05 GMT+02:00
To: dfdl-wg at ogf.org
Subject: [DFDL-WG] [wg-all] Repeating groups in DFDL
For anyone that was at the 19/07 phone meeting, this is what Adam Fox and
I were trying to find a solution to. If anyone knows of a solution, please
contact me or adam.fox at nrl.navy.mil.
----------------------------------------------------------------------------------------------------
Please see the attached xml schema while reading this message.
The problem we want to solve is how to represent a structure that can have
a variable amount of occurences (even zero), and the amount of repeats is
controlled by a one bit field, which we will call"repeatBit". The
repeating structure in this case is "A1". The element before it,
"presentBit", determines if there is at least one occurence of A1. If
presentBit is zero, then A1 has zero occurences. If presentBit is one,
then A1 has AT LEAST one occurence.
The first element in A1 is "repeatBit". What repeatBit does is tells us if
there will be another occurence of A1 after the current occurence. When
repeatBit is zero, then that means we will read through the rest of A1,
then that is the last occurence of A1. As long as repeatBit continues to
be one however, we will read through the rest of A1, then start a new
occurence.
I have included all the known required DFDL notation. Please let me know
what is missing.
EXAMPLE INPUT (results are in base 10):
NOTE: Not all bits are used in these examples. Unused bits should be
ignored for the purpose of the examples.
1) 0111 0101
presentBit = 0
aFieldAfterA1 = 3
2) 1011 1010
presentBit = 1
A1
-repeatBit = 0
-someField = 3
aFieldAfterA1 = 2
3) 1101 0110 0000 0000
presentBit = 1
A1
-repeatBit = 1
-someField = 1
A1
-repeatBit = 0
-someField = 3
aFieldAfterA1 = 0
<repeat_example.xsd>
From: Steve Hanson <smh at uk.ibm.com>
Date: July 20, 2011 10:54:27 GMT+02:00
To: Ryan Farrell <ryan.farrell.ctr at nrl.navy.mil>
Cc: dfdl-wg at ogf.org
Subject: Re: [DFDL-WG] [wg-all] Repeating groups in DFDL
A couple of clarifications if I may....
- In your example, you have someField as being of simple type, can it be
complex type in your real format?
- You said "If presentBit is zero, then A1 has zero occurences". But in
your xsd you have A1 as (implied) minOccurs="1". I think you meant
minOccurs="0"?
Regards
Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
From:
Ryan Farrell <ryan.farrell.ctr at nrl.navy.mil>
To:
dfdl-wg at ogf.org
Date:
19/07/2011 19:12
Subject:
[DFDL-WG] [wg-all] Repeating groups in DFDL
Sent by:
dfdl-wg-bounces at ogf.org
For anyone that was at the 19/07 phone meeting, this is what Adam Fox
and I were trying to find a solution to. If anyone knows of a solution,
please contact me or adam.fox at nrl.navy.mil.
----------------------------------------------------------------------------------------------------
Please see the attached xml schema while reading this message.
The problem we want to solve is how to represent a structure that can
have a variable amount of occurences (even zero), and the amount of
repeats is controlled by a one bit field, which we will call"repeatBit".
The repeating structure in this case is "A1". The element before it,
"presentBit", determines if there is at least one occurence of A1. If
presentBit is zero, then A1 has zero occurences. If presentBit is one,
then A1 has AT LEAST one occurence.
The first element in A1 is "repeatBit". What repeatBit does is tells us
if there will be another occurence of A1 after the current occurence.
When repeatBit is zero, then that means we will read through the rest of
A1, then that is the last occurence of A1. As long as repeatBit
continues to be one however, we will read through the rest of A1, then
start a new occurence.
I have included all the known required DFDL notation. Please let me know
what is missing.
EXAMPLE INPUT (results are in base 10):
NOTE: Not all bits are used in these examples. Unused bits
should be ignored for the purpose of the examples.
1) 0111 0101
presentBit = 0
aFieldAfterA1 = 3
2) 1011 1010
presentBit = 1
A1
-repeatBit = 0
-someField = 3
aFieldAfterA1 = 2
3) 1101 0110 0000 0000
presentBit = 1
A1
-repeatBit = 1
-someField = 1
A1
-repeatBit = 0
-someField = 3
aFieldAfterA1 = 0
[attachment "repeat_example.xsd" deleted by Steve Hanson/UK/IBM] --
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741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
From: Steve Hanson <smh at uk.ibm.com>
Date: July 20, 2011 13:28:47 GMT+02:00
To: dfdl-wg at ogf.org
Cc: DFDL-Technical-Core%IBMGB at uk.ibm.com
Subject: [DFDL-WG] OGF DFDL WG Call Minutes 2011-07-19
Please find minutes of the above meeting on GridForge at:
http://forge.gridforum.org/sf/docman/do/downloadDocument/projects.dfdl-wg/docman.root.current_0.calls/doc16291/2
Regards
Steve Hanson
Architect, DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
From: "Mike Beckerle" <mbeckerle.dfdl at gmail.com>
Date: July 23, 2011 00:43:49 GMT+02:00
To: "'Ryan Farrell'" <ryan.farrell.ctr at nrl.navy.mil>, <dfdl-wg at ogf.org>
Subject: Re: [DFDL-WG] [wg-all] Repeating groups in DFDL
Great example Ryan,
We've spent quite a bit of time over the last several months on textual
formats with these kinds of characteristics, which I would describe as
"occurrances determined by parsing" - that is, you look at the data to
determine "is there another element or not" one by one as they are parsed.
We need to make sure the properties are there to make this work for the
binary case as well.
I actually believe we cannot handle this format right now. We don't have a
property which says to look at the current element to determine whether to
expect a subsequent element, as a way of determining occurrence counts.
Next week we'll add resolving this example to the workgroup actions list.
...mikeb
Mike Beckerle
Senior Technology Leader/Manager
Deloitte Managed Analytics
100 Fifth Avenue, Waltham, MA 02451
Tel/Direct: +1 781 330 0412 | Fax: +1 866 253 3006
www.deloitte.com
-----Original Message-----
From: dfdl-wg-bounces at ogf.org [mailto:dfdl-wg-bounces at ogf.org] On Behalf
Of
Ryan Farrell
Sent: Tuesday, July 19, 2011 2:12 PM
To: dfdl-wg at ogf.org
Subject: [DFDL-WG] [wg-all] Repeating groups in DFDL
For anyone that was at the 19/07 phone meeting, this is what Adam Fox
and I were trying to find a solution to. If anyone knows of a solution,
please contact me or adam.fox at nrl.navy.mil.
----------------------------------------------------------------------------
------------------------
Please see the attached xml schema while reading this message.
The problem we want to solve is how to represent a structure that can
have a variable amount of occurences (even zero), and the amount of
repeats is controlled by a one bit field, which we will call"repeatBit".
The repeating structure in this case is "A1". The element before it,
"presentBit", determines if there is at least one occurence of A1. If
presentBit is zero, then A1 has zero occurences. If presentBit is one,
then A1 has AT LEAST one occurence.
The first element in A1 is "repeatBit". What repeatBit does is tells us
if there will be another occurence of A1 after the current occurence.
When repeatBit is zero, then that means we will read through the rest of
A1, then that is the last occurence of A1. As long as repeatBit
continues to be one however, we will read through the rest of A1, then
start a new occurence.
I have included all the known required DFDL notation. Please let me know
what is missing.
EXAMPLE INPUT (results are in base 10):
NOTE: Not all bits are used in these examples. Unused bits
should be ignored for the purpose of the examples.
1) 0111 0101
presentBit = 0
aFieldAfterA1 = 3
2) 1011 1010
presentBit = 1
A1
-repeatBit = 0
-someField = 3
aFieldAfterA1 = 2
3) 1101 0110 0000 0000
presentBit = 1
A1
-repeatBit = 1
-someField = 1
A1
-repeatBit = 0
-someField = 3
aFieldAfterA1 = 0
From: Steve Hanson <smh at uk.ibm.com>
Date: July 26, 2011 11:58:59 GMT+02:00
To: dfdl-wg at ogf.org
Subject: [DFDL-WG] OGF DFDL WG Call Agenda 2011-07-26
Please find agenda for the above call on GridForge at:
http://forge.gridforum.org/sf/docman/do/downloadDocument/projects.dfdl-wg/docman.root.current_0.calls/doc16304/1
As per action 144 an errata to the spec has been created here:
http://forge.gridforum.org/sf/go/doc16280?nav=1
Regards
Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at 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
-----------------------------------------
Michele Zundo
EOP-PEP
Ground System Definition and Verification Office
European Space Agency, ESTEC
e-mail: michele.zundo at esa.int
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