So I looked into what would be changed in the spec to make the adjustment suggested in this email thread, in intent.

Rewriting the section is very undesirable at this stage for DFDL, so I was looking for incremental changes.

What I came up with is this. In section 14.2.2 simply drop the sentences that mention this idea of an implied SSP, because they suggest the need to reconcile conflicting behaviors in the mixed case. I.e., drop all  "The dfdl:separatorSuppressionPolicy is not applicable and the implied behaviour is  '....'."

With the omission of these sentences, the notion of an implied separator suppression policy that conflicts with one on the sequence goes away. There is only the SSP property of the sequence, and it is either relevant to the decision of whether to expect an item and its separator, or it isn't.

The current descriptions in 14.2.2 of the behavior around suppression for each occursCountKind seem to be correct and match the table in this email thread, except for parsed.

I'm not sure I agree with the assertion in this email thread that ock parsed only makes sense with "anyEmpty" behavior. We currently say in the spec that it has anyEmpty behavior, but if we drop that sentence (per suggestion above), then we would be loosening the behavior to allow empty elements in some cases. 

Suppose:

<sequence dfdl:separatorSuppressionPolicy="trailingEmpty" dfdl:separator="|" dfdl:separatorPosition="infix"
    dfdl:terminator="%NL;"> 
   <element name="a" type="xs:string" maxOccurs="unbounded" dfdl:occursCountKind='parsed'/>
</sequence>

In this case, the array is declared last in its sequence. The occurrences will all be element a, so this is positional. The number of them is determined by OCK parsed, and if enabled, validation will check, in this case, that at least 1 occurrence (the default for minOccurs) appears.

In this case, empty string is a legal value, and we're not strict about trailing separators, so data like:

5|6|7||

is fine isn't it? The 'parsed' means you'll get 2 more empty string elements for the array when parsing that will not be re-created when unparsing, as they would be suppressed. I believe that is ok. There are many formats that can have that sort of asymmetry.

Change the above example to SSP trailingEmptyStrict, and now:

5,6,7||9

Now makes sense and you get one empty string in position 4. On unparsing this empty string would even get written out.

I agree 'parsed' and SSP 'never' don't make sense together (as they don't for OCK implicit), but the other 3 SSPs seem ok to me for declared-last elements. OCK parsed behaves (w.r.t. suppression, and ignoring defaulting and validation) just like OCK implicit with minOccurs 0 and maxOccurs 'unbounded'.

If we want to preserve the current restriction that parsed behaves like 'anyEmpty', then we can stipulate that when OCK is 'parsed', any number of non-empty occurrences and their separators are expected. (I would not be in favor of this.)

As already noted in this thread, we also should add a sentence to stopValue: "The dfdl:stopValue property must not include empty string."

The net result of these changes still isn't all that great, but it does remove one source of confusion - the 'implied' SSP conflict.



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 Mon, Oct 13, 2014 at 10:08 AM, Steve Hanson <smh@uk.ibm.com> wrote:
IBM has discussed this issue at some length internally, and come to the conclusion that the optional and array elements in a sequence should follow the separator suppression policy (SSP), and not have an implied SSP which is at odds with the sequence's SSP. In the table below, cells marked with a cross imply a schema definition error, and cells marked ok imply that there is a behaviour of the element for that OCK which is in keeping with the SSP of the sequence.
SSP (1)
OCK
fixed implicit expression parsed stopValue (2)
never ok ok ok x (5) ok (6)
trailingEmpty
trailingEmptyStrict 		ok (3) ok ok (4) x (5) ok (6)
anyEmpty ok (3) ok ok (4) ok ok


Notes:
(1) SSP property applies only to an ordered sequence. An unordered sequence assumes 'anyEmpty' (as all optional/array elements must be 'parsed')
(2) Missing restriction - for 'stopValue' the dfdl:stopValue property must not include empty string.
(3) maxOccurs provides count, so nothing is eligible for suppression, so SSP has no practical effect (same as a required element)
(4) infoset provides count, so nothing is eligible for suppression, so SSP has no practical effect (same as a required element)
(5) 'parsed' only makes sense with 'anyEmpty'
(6) Because a stop value must appear, and from (2) empty string is not allowed, SSP has no practical effect.

The issue of maxOccurs = '0' is discussed in a separate email.

Regards
 
Steve Hanson
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848
----- Forwarded by Steve Hanson/UK/IBM on 13/10/2014 14:40 -----

From:        Mike Beckerle <mbeckerle.dfdl@gmail.com>
To:        Steve Hanson/UK/IBM@IBMGB,
Cc:        "dfdl-wg@ogf.org" <dfdl-wg@ogf.org>
Date:        29/08/2014 21:21
Subject:        Re: [DFDL-WG] Fw: Action 260



I reviewed this. It looks good to me.

The note at the bottom that we don't say what happens on a zero-trip I.e., a represented element, but where occursCount evaluates to 0, is a useful clarification also.

Do we want to create an erratum for this?

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 Thu, Aug 28, 2014 at 10:13 AM, Steve Hanson <smh@uk.ibm.com> wrote:
Please review for Tuesday's WG call ...

Regards
 
Steve Hanson
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848
----- Forwarded by Steve Hanson/UK/IBM on 28/08/2014 15:02 -----

From:        Steve Hanson/UK/IBM
To:        dfdl-wg@ogf.org,
Date:        06/08/2014 13:50
Subject:        Fw: [DFDL-WG] Action 260


So my suggestion below, to wrap the array in a sequence, does not work; it just moves the problem down into the new sequence.

After much deliberation, we think that the definitions of Positional sequence and Non-positional sequence should not be viewed as driving the behaviour of a sequence, but simply as the resultant characteristics of a sequence that has certain properties. That leaves modellers free to mix occursCountKinds, as in Tim's example. No need for any new SDE scenarios.  
Positional sequence - Each occurrence in the sequence can be identified by its position in the data. Typically the components of such a sequence do not have an initiator. In some such sequences, the separators for optional zero-length occurrences may or must be omitted when at the end of the group. In DFDL, a sequence is considered positional if it contains only required elements and/or optional and array elements that have dfdl:occursCountKind 'implicit', 'fixed' or 'expression', and it has dfdl:separatorSuppressionPolicy 'never', 'trailingEmptyStrict'  or 'trailingEmpty'.

Non-positional sequence - Occurrences in the sequence cannot be identified by their position in the data alone. Often the components of such a sequence have an initiator. Such sequences sometimes allow the separator to be omitted for optional zero-length occurrences anywhere in the sequence. Speculative parsing might need to be employed by to identify each occurrence. In DFDL, a sequence is non-positional if it contains any optional or array elements that have dfdl:occursCountKind 'parsed' or 'stopValue', and/or it has dfdl:separatorSuppressionPolicy 'anyEmpty'.

See parallel email for action 261 that ensures 'expression' behaves itself.

One behaviour that is missing from the spec. For a sequence with separators, what is expected in the data stream if occursCount = 'fixed' / 'implicit' and maxOccurs = '0', or occursCountKind = 'expression' and occursCount evaluates to 0 ?  We believe that no separator should be expected when parsing and none output when unparsing (same behaviour as inputValueCalc).

Regards
 
Steve Hanson
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848
----- Forwarded by Steve Hanson/UK/IBM on 06/08/2014 12:42 -----

From:        Steve Hanson/UK/IBM
To:        Tim Kimber/UK/IBM@IBMGB,
Cc:        dfdl-wg@ogf.org, dfdl-wg-bounces@ogf.org
Date:        30/06/2014 10:04
Subject:        Re: [DFDL-WG] Action 260



You would wrap the array and it's count in a sequence. Then the 'count+array' is treated as a single entity as far as the parent sequence is concerned.

Regards
 
Steve Hanson
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848



From:        Tim Kimber/UK/IBM@IBMGB
To:        dfdl-wg@ogf.org,
Date:        26/06/2014 20:06
Subject:        Re: [DFDL-WG] Action 260
Sent by:        dfdl-wg-bounces@ogf.org



Before we settle one way or the other, I would like the following data format to be taken into consideration.

chars,5,A,B,C,D,E,integers,1,2,3
chars,3,C,,,integers,2,10,11

I am assuming that the occursCountKind for the arrays is 'expression' and the occursCount refers to the integer field that precedes the array. In order to represent the empty strings on the second line it is essential to specify SSP as 'trailingEmpty' or 'never'. If we disallow the combination of ock='expression' and SSP='trailingEmpty' then how would this format be modelled?

regards,

Tim Kimber,
Technical Lead for IBM Integration Bus Healthcare Pack
Hursley, UK
Internet:  kimbert@uk.ibm.com
Tel. 01962-816742  
Internal tel. 37246742




From:        Mike Beckerle <mbeckerle.dfdl@gmail.com>
To:        Steve Hanson/UK/IBM@IBMGB,
Cc:        "dfdl-wg@ogf.org" <dfdl-wg@ogf.org>
Date:        25/06/2014 16:25
Subject:        Re: [DFDL-WG] Action 260
Sent by:        dfdl-wg-bounces@ogf.org



I prefer choice (a) for two reasons

* It is more restrictive and therefore more conservative (preserving freedom to change in future if needed)
* If a user has a positional data format, you don't want them to even have to understand the concept of speculation in order to model their data. So choice (a) allows a simpler description that doesn't need to introduce the notion that the parser might be speculation.


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, Jun 25, 2014 at 5:20 AM, Steve Hanson <smh@uk.ibm.com> wrote:
260
Positional and non-positional sequences (All)
10/6: Spec defines the above but also allows different occursCountKinds within the same sequence which may have different (implied) separatorSuppressionPolicy, which results in a sequence which is a mixture of both. Should this be allowed? If so what are the rules? Can certain combinations be disallowed?
17/6: IBM have discussed internally and will submit a proposal.

In the spec we define Positional Sequence and Non-Positional Sequence:

Positional sequence - Each occurrence in the sequence can be identified by its position in the data. Typically the components of such a sequence do not have an initiator. In some such sequences, the separators for optional zero-length occurrences may or must be omitted when at the end of the group. A positional sequence can be modelled by setting dfdl:separatorSuppressionPolicy to 'never', 'trailingEmptyStrict'  or 'trailingEmpty'.

Non-positional sequence - Occurrences in the sequence cannot be identified by their position in the data alone. Typically the components of such a sequence have an initiator. Such sequences allow the separator to be omitted for optional zero-length occurrences anywhere in the sequence. Speculative parsing is employed by the parser to identify each occurrence.  A non-positional sequence can be modelled by setting dfdl:separatorSuppressionPolicy to 'anyEmpty'.

The problem is that the setting of dfdl:separatorSuppressionPolicy is only examined for child elements with dfdl:occursCountKind 'implicit'.  For other dfdl:occursCountKinds, there is the concept of an 'implied' dfdl:separatorSuppressionPolicy:

When dfdl:occursCountKind is 'fixed' then ... the implied behaviour is 'never'.

When dfdl:occursCountKind is 'expression' ... the implied behaviour is 'never'.

When dfdl:occursCountKind is 'parsed' ... the implied behaviour is   'anyEmpty'.

When dfdl:occursCountKind is 'stopValue' ...the implied behaviour is 'anyEmpty'.

So if a Positional sequence as defined above contains children with dfdl:occursCountKind 'parsed' or 'stopValue' then surely it is no longer a Positional sequence.

A solution to this is to prevent the appearance of certain values of dfdl:occursCountKind within a Positional sequence. However, precisely which values to outlaw is subject to interpretation of the phrase "Each occurrence in the sequence can be identified by its position in the data". Is this intended to mean:

a) an observer of the raw data can identify an occurrence of an element in the sequence solely by counting separators

=> SDE if 'parsed', 'stopValue' or 'expression' ** appeared in a Positional sequence;

** Although 'expression' would appear to be like 'fixed' it actually breaks a) so must be included in the SDE list.

or

b) a parser does not have to speculate to identify an occurrence of an element in the sequence

=> SDE only if 'parsed' appeared in a Positional sequence.

Note that it is possible to wrap a 'parsed' etc element in a local sequence or another element to avoid an SDE. But this could still be seen as a violation of a) if the separators of both are the same, as the observer can not count the separators. So should the rule be applied recursively, ie, a Positional sequence can not contain a non-Positional sequence unless the separators are different?

Regards

Steve Hanson
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@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

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Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU

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