[DFDL-WG] Agenda for DFDL WG call - 2008-01-30

Tue Jan 29 20:05:17 CST 2008

Thanks Alan and Steve for some agenda topics:

Follow up the items from last week 

 - Specification  drafts   -   I need updates from everyone to produce next
spec draft 

-  Expression language  -  Comments from only Steve H. so far 

- Property precedence  - Any more comments/discussion 

- UML for DFDL schema - status update 

- Entity proposal updates?

Discussion for this call 

- White space 

- Steve's items (??) 

- OGF presentation

Other Topics?

From: Steve Hanson [mailto:smh at uk.ibm.com] 
Sent: Tuesday, January 29, 2008 1:10 PM
To: Mike Beckerle
Cc: Alan Powell
Subject: Agenda for DFDL WG call

Hi Mike - possible agenda items for tomorrow. 

Regards, Steve

Steve Hanson
WebSphere Message Brokers
Hursley, UK
Internet: smh at uk.ibm.com
Phone (+44)/(0) 1962-815848 
----- Forwarded by Steve Hanson/UK/IBM on 29/01/2008 17:55 ----- 

Alan Powell/UK/IBM 

29/01/2008 17:25 

To

Steve Hanson/UK/IBM at IBMGB 

cc

Subject

Fw: [DFDL-WG] DFDL: Minutes from OGF WG call,        23 Jan 2007 *CORRECTED*

Steve 

I will try to make the WG call tomorrow but may be still on a course. 

We need to follow up the items from last week 

 - Specification  drafts   -   I need updates from everyone to produce next
spec draft 

-  Expression language  -  Comments from only you so far 

- Property precedence  - Any more comments/discussion 

- UML for DFDL schema - status update 

- Entity proposal  - I should have updated as a result of last weeks
discussion but haven't had time 

Discussion for this call 

- White space 

- Your items.   We did discuss them a bit but mostly in the context of white
space. 

Alan Powell

MP 211, IBM UK Labs, Hursley,  Winchester, SO21 2JN, England
Notes Id: Alan Powell/UK/IBM     email: alan_powell at uk.ibm.com  
Tel: +44 (0)1962 815073                  Fax: +44 (0)1962 816898

----- Forwarded by Alan Powell/UK/IBM on 29/01/2008 17:19 ----- 

Steve Hanson/UK/IBM at IBMGB 
Sent by: dfdl-wg-bounces at ogf.org 

28/01/2008 08:51 

To

dfdl-wg at ogf.org 

cc

Subject

Re: [DFDL-WG] DFDL: Minutes from OGF WG call,        23 Jan 2007 *CORRECTED*

Sorry I couldn't make the call.  Some comments: 

a) we need both WSP and OWSP if DFDL delimiter properties can only specify a
single value. If they can specify a list of values then you can get away
with only needing WSP 
      eg, dfdl:terminator="@ @%WSP;" 
b) if we make WSP mean a single white space character, we need a second
entity for multiple white space characters. 

It doesn't look like you got round to discussing the other items I sent in
(below)? Let's do that next call. 

1) One way to handle the situation where the terminator can vary is to allow
the DFDL markup properties (dfdl:terminator, dfdl:separator, etc) to be
lists, just like we already do for dfdl:nullValues. (IBM's WTX has this
capability). 

2) We've allowed the prefix of a prefixed length to be explicitly described
as a non-event field using dfdl:lengthPrefixType. Should we permit this for
markup properties?  Instead of supplying a list of possible values, you
supply a simple type with enums for the values. This could be viewed as an
alternative/complementary to 1). There is a limitations - because we are
using XSDL enumeration facet, we are constrained by its syntax so I don't
see how we could use our own entity scheme or expressions. Also, I suspect
that enums are inherently unordered so we'd need a way of saying which to
use on output (use an element of simple type and use XSDL default
attribute?).  Lastly, we should not force a user to model an initiator as an
element/type - most users just see it as a piece of text so just entering
the value must still be allowed. 

3) Let's say my delimiter is dynamically defined at the start of the data,
like EDI allows. We would handle that in DFDL using an expression or
variable. However, EDI also allows random white space to appear after the
delimiter. Can our expression/entity syntaxes handle this?  Does this
preclude use of 1) or 2)?   

Regards, Steve

Steve Hanson
WebSphere Message Brokers
Hursley, UK
Internet: smh at uk.ibm.com
Phone (+44)/(0) 1962-815848 

Ian W Parkinson/UK/IBM at IBMGB 
Sent by: dfdl-wg-bounces at ogf.org 

24/01/2008 16:19 

To

dfdl-wg at ogf.org 

cc

Subject

[DFDL-WG] DFDL: Minutes from OGF WG call, 23 Jan 2007 *CORRECTED*

A small correction. with thanks to Simon - it was Steve (rather than Simon)
who had previously attracted a reasonable audience at the OGF conference. 

Ian 

Open Grid Forum: Data Format Description Language Working Group 

Weekly Working Group Conference Call 
17:00 GMT, 23 Jan 2008 

Attendees 
Mike Beckerle (Oco) 
Simon Parker (PolarLake) 
Ian Parkinson (IBM) 
Alan Powell (IBM) 

Apologies 
Steve Hanson (IBM), Suman Kalia (IBM) 

1. OGF22 
The DFDL session at OGF22 is now booked for the Monday afternoon, and Mike
has registered to attend. Mike will present our updated status, and Alan
promised to upload the last set of presented slides to GridForge so that
Mike can update them. Alan asked whether we should attempt to drum up
interest in the DFDL session to encourage attendence; Simon thought that
advertising may not make much difference and that Steve had a reasonable
audience when he presented. 

2. Specification drafts 
Steve and Alan had previously assigned ownership of individual items from
Mike's plan of contents for the next few drafts. Alan will assemble the next
draft, due at the end of the month, and asked for input as soon as possible.

Looking at the plan for the next, "vX+1", draft, the group reported the
following status: 

*	Nulls/default/optionals - Mike reported no update. 
*	Description of schema components - Simon is still working on this. 
*	Regular expressions for lengths - Alan reported no progress. 
*	Expression language - Alan will shortly distribute a new version of
the proposal for review. 
*	valueCalc - Mike is still to write this. 
*	Property precedence - Following a discussion on the call last week,
please provide review comments. Mike will add this to the agenda for next
week. 
*	Entities - Alan's recent proposal is to be discussed on the current
call. 
*	White space handling - Discussion is ongoing, and Steve is to make a
proposal.

The plan calls for subsequent versions of the specification, including the
following items with status: 

*	Supplements - Steve is working to update the supplements 
*	Speculative parsing - IBM has internally been discussing and
reviewing WTX function, though no documentation presently exists covering
this.

3. UML diagrams 
Simon is revising the UML diagrams which describe the DFDL schema
components. The previous meeting minutes included a number of comments on
these diagrams, and the group took this opportunity to look at some of those
comments: 

"...I think it would be better to use the open source XML schema model as
source model and show relationship of DFDL Annotations attached to the XSD
schema model" - Mike noted that DFDL makes use of annotations on objects
which are absent from the XSD schema model, and hence that it may be
unnatural to base the DFDL schema model directly on the XSD model. Simon
suggested that it would be cleanest to describe a modified version the XSD
model including those XSD elements that we need to annotate, and use this as
a basis for the DFDL model. 

"The current diagram suggests that 'variable definition' can both be part of
a format base or as a standalone annotation (outside of a format). Is this
true?" - Mike suggested that variable definitions don't have to be part of a
format block: so, yes, this is true. 

Mike agreed to respond further to the set of comments by email. 

4. Review of Entities proposal 
Alan has distributed a proposal covering entities in DFDL, intended to allow
characters which are disallowed by XML1.0 (or XML1.1) to be included in DFDL
schemas. These follow a similar syntax to XML, using % instead of & as an
escape, with an additional mechanism for specifying raw data. This latter is
intended to supplant the escaping mechanism described in current versions of
the specification (which also uses % as an escape). 

The group felt that the description of the raw data entities should not be
cast in terms of characters and character sets, but rather in terms of
bytes. If treated as characters, schemas may need to be written when moving
from single-byte to double-byte character sets; further, this incorrectly
implies some codepage conversion is involved. 

The proposal also introduces a list of predefined names for certain common
control characters. Mike asked whether these are the existing XML names -
Alan replied that XML does not define names for control characters. 

Ian asked how we should represent the literal % character in strings given
this form of escaping. The present draft of the specification uses "%%" to
handle this; Simon suggested a string like "%pc;". The meeting felt that %%
might be marginally preferable. 

Finally, the proposal defines some labels which aim to reduce the complexity
of dealing with whitespace and newlines. The %NL; entity represents a
newline on "the target platform" - Mike observed that DFDL presently does
not have a concept of a target platform. Alan felt it important that a
single DFDL schema be able to generate output documents targetted at
different platforms. Mike proposed that we introduce a new property,
"generatedNewLine", which describes the meaning of %NL; during unparse, and
that %NL; should be tolerant of any common new line representation during
parse. The group discussed whether this could instead be handled using a
list of optional new line values, however this would not support schema
portability. Simon suggested we introduce another new property to mean that
%NL; should be the conventional new line representation on the platform on
which an engine is running, however Mike pointed out that this simply
requires appropriate configuration of the generatedNewLine property. 

%WSP; and %OWSP; are introduced to mean any whitespace, and optional
whitespace. This will be useful in describing some formats which allow
arbitrary whitespace, such as MIME. Mike pointed out that we could model
such whitespace using hidden fields, but that these entities may make a
schema clearer. PolarLake have found that only one such label is necessary,
which means, "one or more whitespace characters", and that this needs only
to be made available as a delimiter - Mike agreed that this label may
represent a special type of delimiter rather than a general purpose entity.
Alan would like to work through the potential use cases to see if we can
restrict it in this fashion, and will update the proposal to specify that
these relate to just one character. Simon suggested we could introduce an
extra label, perhaps %WPS*; to match multiple whitespace characters. 

Meeting closed, 18:15 

Ian Parkinson
WebSphere ESB Development
Mail Point 211, Hursley Park, Hursley, Winchester, SO21 2JN, UK

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