[DFDL-WG] DFDL pointer & offset proposal
Bradd Kadlecik
braddk at us.ibm.com
Thu Dec 12 10:40:28 EST 2019
Updated with comments:
(See attached file: DFDL_Indirection_v2.docx)
Regards,
Bradd Kadlecik
z/TPF Development
Phone: 1-845-433-1573 2455 South Rd
E-mail: braddk at us.ibm.com Poughkeepsie, NY
12601-5400
United States
From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: Bradd Kadlecik <braddk at us.ibm.com>
Cc: DFDL-WG <dfdl-wg at ogf.org>
Date: 10/16/2019 05:43 PM
Subject: [EXTERNAL] Re: [DFDL-WG] DFDL pointer & offset proposal
I added some comments to your original document. Attached.
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 Wed, Sep 25, 2019 at 12:55 PM Bradd Kadlecik <braddk at us.ibm.com> wrote:
Here's what I've put together regarding the pointer & offset proposal for
the next meeting's review.
(See attached file: DFDL_Indirection.docx)
Regards,
Bradd Kadlecik
z/TPF Development
Phone: 1-845-433-1573 2455 South Rd
E-mail: braddk at us.ibm.com Poughkeepsie, NY
12601-5400
United States
Inactive hide details for Steve Hanson---04/05/2019 12:42:34 PM---Regards
Steve Hanson---04/05/2019 12:42:34 PM---Regards
From: Steve Hanson/UK/IBM
To: Bradd Kadlecik/Poughkeepsie/IBM at IBMUS
Cc: "Mike Beckerle" <mbeckerle at tresys.com>, "Michele Zundo" <
michele.zundo at esa.int>
Date: 04/05/2019 12:42 PM
Subject: Re: Latest OGF DFDL WG Call Minutes
|-+-----------------------------------------------------------------------|
|N|Action |
|o| |
|-+-----------------------------------------------------------------------|
|3|Create example scenarios to illustrate offset & pointer requirements |
|0|(Bradd) |
|9|5/4/19: Daffodil have a draft proposal for offset support, TPF have |
| |experimental implementation for pointer support. Need examples to show |
| |the requirement, especially unparsing. |
|-+-----------------------------------------------------------------------|
Regards
Steve Hanson
IBM Hybrid Integration, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh at uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890
Note: I work Tuesday to Friday
Inactive hide details for Steve Hanson---05/04/2019 10:29:24---I can see
a difference between offsets and pointers. If I folloSteve
Hanson---05/04/2019 10:29:24---I can see a difference between offsets and
pointers. If I follow an offset and parse an element x t
From: Steve Hanson/UK/IBM
To: Bradd Kadlecik/Poughkeepsie/IBM at IBMUS
Cc: "Mike Beckerle" <mbeckerle at tresys.com>, "Michele Zundo" <
michele.zundo at esa.int>
Date: 05/04/2019 10:29
Subject: Re: Latest OGF DFDL WG Call Minutes
I can see a difference between offsets and pointers. If I follow an
offset and parse an element x then I won't automatically jump back to
where I was - the next element y I parse will continue from location
offset + length x unless I use offset again to jump back to the original
location. If I follow a pointer and parse an element x, then the next
element y I parse will continue from original location + length(pointer).
Regards
Steve Hanson
IBM Hybrid Integration, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh at uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890
Note: I work Tuesday to Friday
Inactive hide details for Steve Hanson---04/04/2019 09:42:36---This is a
proposal from the Daffodil team for offset support, neSteve
Hanson---04/04/2019 09:42:36---This is a proposal from the Daffodil team
for offset support, needed for formats like TIFF and if we
From: Steve Hanson/UK/IBM
To: Bradd Kadlecik/Poughkeepsie/IBM at IBMUS
Cc: "Mike Beckerle" <mbeckerle at tresys.com>, "Michele Zundo" <
michele.zundo at esa.int>
Date: 04/04/2019 09:42
Subject: Re: Latest OGF DFDL WG Call Minutes
This is a proposal from the Daffodil team for offset support, needed for
formats like TIFF and if we ever want to be able to handle zip files.
https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=74687382
I think this proposal can implement your requirement - the dfdl:offset
property can be an expression that refers to another element (your
pointer element), which can be hidden so as not to appear in the infoset.
I think what you are proposing is a more convenient way of handling
offsets that are defined dynamically in the data, as opposed to defined
statically with fixed values (though as I said below I need unparsing
explained). But I may be mis-understanding your use cases.
Regards
Steve Hanson
IBM Hybrid Integration, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh at uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890
Note: I work Tuesday to Friday
Inactive hide details for Bradd Kadlecik---03/04/2019 16:50:13---Ok, I'll
work on putting a scenario together for various pointBradd
Kadlecik---03/04/2019 16:50:13---Ok, I'll work on putting a scenario
together for various pointer setups (array, complex element, str
From: Bradd Kadlecik/Poughkeepsie/IBM
To: Steve Hanson/UK/IBM at IBMGB
Cc: "Mike Beckerle" <mbeckerle at tresys.com>, "Michele Zundo" <
michele.zundo at esa.int>
Date: 03/04/2019 16:50
Subject: Re: Latest OGF DFDL WG Call Minutes
Ok, I'll work on putting a scenario together for various pointer setups
(array, complex element, string) and show how it looks for both the JSON
and the binary.
I'm currently at a conference this week but will be returning late
Thursday so expect to be available for the call Friday.
I presented the TPF specific pointer implementation at the conference
this week and there are some that will be trying to use it soon.
Regards,
Bradd Kadlecik
z/TPF Development
Phone: 1-845-433-1573 2455 South Rd
E-mail: braddk at us.ibm.com Poughkeepsie, NY
12601-5400
United States
Inactive hide details for Steve Hanson---04/03/2019 10:29:25 AM---Hi
Bradd I have a few questions please ... inline below.Steve
Hanson---04/03/2019 10:29:25 AM---Hi Bradd I have a few questions
please ... inline below.
From: Steve Hanson/UK/IBM
To: Bradd Kadlecik/Poughkeepsie/IBM at IBMUS
Cc: dfdl-wg at ogf.org, "Mike Beckerle" <mbeckerle at tresys.com>, "Michele
Zundo" <michele.zundo at esa.int>
Date: 04/03/2019 10:29 AM
Subject: Re: Latest OGF DFDL WG Call Minutes
Hi Bradd
I have a few questions please ... inline below.
I'm still going to need a real worked example, starting with some actual
data and its schema, what it appears like after paring in the infoset,
and how unparsing lays it back out again.
Are you able to make the rescheduled call this Friday?
Regards
Steve Hanson
IBM Hybrid Integration, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh at uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890
Note: I work Tuesday to Friday
Inactive hide details for Bradd Kadlecik---27/02/2019
22:22:48---Regarding proposal for offsets and pointers: The following are
Bradd Kadlecik---27/02/2019 22:22:48---Regarding proposal for offsets and
pointers: The following are the properties to be defined:
From: Bradd Kadlecik/Poughkeepsie/IBM
To: Steve Hanson/UK/IBM at IBMGB
Cc: dfdl-wg at ogf.org, "Mike Beckerle" <mbeckerle at tresys.com>, "Michele
Zundo" <michele.zundo at esa.int>
Date: 27/02/2019 22:22
Subject: Re: Latest OGF DFDL WG Call Minutes
Regarding proposal for offsets and pointers:
The following are the properties to be defined:
SMH: I was expecting to see these properties only on dfdl:element,
especially as you say '...the element contents... ?
indirectKind Enum
Valid values 'pointer', 'offset' (there is also a thought of objectId or
refId for handling BSON but not at this time)
Specifies the type of indirection used to access the element contents in
the data stream.
Annotation: dfdl:element, dfdl:simpleType, dfdl:choice, dfdl:sequence,
dfdl:group
SMH: I am missing the distinction between offset and pointer. Is one
relative to current position and the other relative to start of
bitstream?
SMH: In earlier DFDL proposals for offset support, we had used the term
to refer to a property to be used to establish position of the current
element instead of assuming the current element followed straight after
the previous one. It would allow sparse modelling of fixed structures.
The offset could be relative to start of bitstream or some other point. I
don't think that's what you mean when you say 'offset' so I will refer to
your new concept as 'pointer'.
SMH: Assuming that indirectKind is a normal DFDL property, it can be in
scope. It would therefore need to have an enum 'None' which would be the
default used in most schemas.
indirectLength Non-negative Integer or DFDL expression
Specifies the length of the indirection in units according to the
indirectUnits property.
Annotation: dfdl:element, dfdl:simpleType, dfdl:choice, dfdl:sequence,
dfdl:group
indirectUnits Enum
Valid values 'bytes','bits'
Specifies the units to be used for reading or writing the indirection
according to indirectLength.
The default value is 'bytes'.
Annotation: dfdl:element, dfdl:simpleType, dfdl:choice, dfdl:sequence,
dfdl:group
SMH: I think a better approach is to provide a property
dfdl:indirectType, instead of indirectLength/indirectUnits, which refers
to a simple type (not element) that carries its own lengthKind, length &
lengthUnits properties. Similar idea to dfdl:prefixLengthType. That
allows a lot of flexibility on how the pointer can appear.
offsetBase non-empty string containing an absolute or relative XPath
expression for the base element.
Annotation: dfdl:element, dfdl:simpleType, dfdl:choice, dfdl:sequence,
dfdl:group
The proposal would be to have the contents of the indirection be after
the LeadingAlignment and before the TrailingAlignment. This would mean
the aligment and skip factors apply to the indirection values in the data
stream instead of the the contents of the indirection.
SMH: Agree.
This also then means in an array element, each element has its own
indirection value (pointer or offset) and the alignment,skip factors then
apply to each of these indirection values.
SMH: Do you mean '...each occurrence...' ?
It would be thought that the indirection values apply only to the data
stream and not the infoset. During parse when the infoset is populated
from the data stream, the indirection values are replaced by the
contents. During unparse, the indirection values don't exist in the
infoset and are created during the writing to/creation of the data
stream.
SMH: I agree that the indirection should be a purely physical thing, but
I am not clear how the value is filled in when unparsing. Where does the
value come from? outputValueCalc? Or maybe it's not needed when
unparsing, and the data is always contiguous?
For pointers, a null pointer creates the scenario of either nil
representation or empty representation depending on whether or not
nillable is defined as true. Unless default values (or 0 occurrence) are
defined for all underlying content, then this is a processing error.
During unparse, the only scenario in which a null pointer would be
created is for a nil representation.
SMH: This needs more thought. The nil & default properties apply to the
contents of the indirection, not to the pointer. If you want to give a
nil semantic to the pointer value itself, then that would require a new
enum for dfdl:nilKind. I don't see why a pointer value 0 can't be treated
like any other indirection value. A missing pointer is an error - it must
be present - there is no way to control optionality because
minOccurs/maxOccurs apply to the contents. (Alternatively, if you want
the concepts of nil, default, occurs to apply to the indirect value, then
dfdl:indirectType could point at an element instead of a simple type -
but that seems way too over engineered).
Examples:
The following is the definition for the address of a null-terminated
string in which the string address may be NULL as indicated by a nillable
value of true:
<xs:element name="myString" type="xs:string" dfdl:lengthKind="delimited"
dfdl:encoding="UTF-8" dfdl:terminator="%NUL;" dfdl:indirectKind="pointer"
dfdl:indirectLength="8" dfdl:indirectUnits="bytes" nillable="true" />
The following is the definition for an array of three 4 byte addresses of
a complex element defined by ns0:myStruct:
<xs:element name="myArray" type="ns0:myStruct" dfdl:lengthKind="implicit"
dfdl:indirectKind="pointer" dfdl:indirectLength="4"
dfdl:indirectUnits="bytes" minOccurs="3" maxOccurs="3"
dfdl:occursCountKind="fixed" />
The following is the definition for a 4 byte offset to a 100 byte
hexBinary value from the start of the parent element definition:
<xs:element name="myData" type="xs:hexBinary" dfdl:lengthKind="explicit"
dfdl:length="100" dfdl:lengthUnits="bytes" dfdl:indirectKind="offset"
dfdl:indirectLength="4" dfdl:indirectUnits="bytes"
dfdl:offsetBase=".." />
SMH: I don't see how unparsing works. What provides the value?
The proposal would also allow for the following optional item but I don't
currently see a need for this:
dfdl:offsetKind with values "startToStart" or "endToStart" - indicates if
the offset is from the start of the base element or the end of the base
element.
I tried getting this out before my vacation so it might take a little bit
to respond for issues. Thank you for your time.
Regards,
Bradd Kadlecik
z/TPF Development
Phone: 1-845-433-1573 2455 South Rd
E-mail: braddk at us.ibm.com Poughkeepsie, NY
12601-5400
United States
Inactive hide details for Steve Hanson---02/07/2019 12:32:26 PM---Please
find minutes from the latest call at https://redmine.oSteve
Hanson---02/07/2019 12:32:26 PM---Please find minutes from the latest
call at https://redmine.ogf.org/projects/dfdl-wg/newsRegards Ste
From: Steve Hanson/UK/IBM
To: dfdl-wg at ogf.org
Cc: "Mike Beckerle" <mbeckerle at tresys.com>, "Michele Zundo" <
michele.zundo at esa.int>, Bradd Kadlecik/Poughkeepsie/IBM at IBMUS
Date: 02/07/2019 12:32 PM
Subject: Latest OGF DFDL WG Call Minutes
Please find minutes from the latest call at
https://redmine.ogf.org/projects/dfdl-wg/news
Regards
Steve Hanson
IBM Hybrid Integration
Architect, IBM DFDL,
Co-Chair, OGF DFDL Working Group
smh at uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890
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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