Suman, comments to yours in pink

Regards

Steve Hanson
Architect, IBM Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848

From: Suman Kalia <kalia@ca.ibm.com>
To: Tim Kimber/UK/IBM@IBMGB,
Cc: dfdl-wg@ogf.org, dfdl-wg-bounces@ogf.org
Date: 15/08/2013 15:31
Subject: Re: [DFDL-WG] Direct dispatch choice clarifications
Sent by: dfdl-wg-bounces@ogf.org

comments in green

Suman Kalia
IBM Canada Lab
WMB Toolkit Architect and Development Lead
Tel: 905-413-3923 T/L 313-3923
Email: kalia@ca.ibm.com

For info on Message broker
http://www.ibm.com/developerworks/websphere/zones/businessintegration/wmb.html

From: Tim Kimber <KIMBERT@uk.ibm.com>
To: dfdl-wg@ogf.org,
Date: 08/15/2013 09:58 AM
Subject: Re: [DFDL-WG] Direct dispatch choice clarifications
Sent by: dfdl-wg-bounces@ogf.org

See comment in <TK> tags.

regards,

Tim Kimber, DFDL Team,
Hursley, UK
Internet: kimbert@uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742

From: Steve Hanson/UK/IBM@IBMGB
To: dfdl-wg@ogf.org,
Date: 15/08/2013 12:57
Subject: [DFDL-WG] Direct dispatch choice clarifications
Sent by: dfdl-wg-bounces@ogf.org

Looking at this in more detail prior to writing up behaviour for section 9, there are a couple of things missing from the spec or that need clarification:

1) Description of elementID property should say that empty string is not allowed (this was in the erratum).

2) Should say that an elementID on an elementRef overrides any elementID on the global element (this was in the erratum).

3) Section 15.1.2 says that is a schema definition error if the elementId values of global elements are not unique within a given namespace. I don't see where namespace comes into this, the elementID is just a string so surely it needs to be unique across namespaces? (Strictly elementID needs only to be unique across the global elements involved in each specific choice, but it was minuted that global uniqueness was desirable to allow future xs:any support).
<TK>
In XML Schema, an xs:any does not, in general, match all global elements. The 'namespace' attribute can narrow the set to elements from a specified list of namespaces. There is no way in XML Schema 1.0 to further narrow the xs:any, So the rule is designed to ensure that future usage of xs:any when a single namespace is specified and processContents!='skip' does not throw up schema definition errors. However...I note that XML Schema 1.1 allows a new way to narrow the scope of an xs:any ( by specifying a list of not-included QNames ). My feeling is that the unique-within-namespace check is fragile.
</TK>

<SK>
As per my recollection, we put the uniqueness rules across namespaces to accommodate chameleon namespaces. Consider a global element E1 in notarget namespace having elementID E1_ID and is included in 2 schemas with different target namespaces say TNS1 and TNS2.. Consider a choice containing element references TNS1:E1 and TNS2:E1, in order to disambiguate these elements in the context choice, the element ID has to be unique in the context of namespace. This is somewhat an edge case but can come more prevalent when the support for xs:any is provided.
</SK>

SMH: In the choice, the element refs to TNS1:E1 and TNS2:E1 both have an elementID string 'E1_ID' from the original E1 global element. In the choice, this is an error because the elementID is not unique in the choice (we match the result of the choiceBranchRef expression, which returns a string not a QName). The only way round this is to override the elementID on one of the element refs (see 2 above) and set a value that is unique. That then works. But that does not help the (future) xs:any scenario, where there is no element ref to carry the override. I think the chameleon namespace scenario will always cause a problem with xs:any because our elementIDs are strings not QNames.

I think we should leave a global element uniqueness check out of DFDL 1.0. It doesn't actually future proof anything, as once I use xs:any the whole nature of the xsd changes.

4) Spec does not explicitly say that when choiceBranchRef is present each branch of the choice must have an elementID. This must be the case, as otherwise a choice branch will never be accessible.

5) Tim has suggested that if an element was silent about elementID, the local name of the element could be used instead. So conceptually an element would have an 'effective elementID'. This makes modelling easier if the 'tag' in the data is the same as the element name.
<TK>...or if the element name is derivable from the 'tag' using a simple XPath expression</TK> SMH: True.
The validation checks would need to ensure that the set of 'effective elementIDs' was unique; for the global element check as currently specified (see 3) this would mean that all global elements must have unique local names, unless an elementID is carried - I think this is too limiting.

SMH: While defaulting to the local name sounds attractive, I can't convince myself that it won't cause problems if we add xs:any in DFDL 2.0 and multiple/chameleon namespaces are involved.

SMH: Conclusion: For DFDL 1.0 we take the conservative position and say that you must specify an elementID on an element that is used in a choice with choiceBranchRef and it must be unique in the context of the choice only. No global uniqueness check is made.

From minutes of 17th April 2012.

145

Provide a 'dispatch' way of discriminating a choice for better performance of the envelope/payload use case (Steve, Mike, Suman)
12/7: See minutes. Need to choose a proposal and flesh out.
19/07: Waiting for proposals
26/07: Waiting for proposals
16/08: Waiting for proposals. Suman added to action.
...
1/11: Steve to send a proposal
...
21/03: Steve has sent a proposal. Mike has sent a counter proposal. Steve to respond.
28/03: Steve has sent a revised proposal. Review for discussion next week. Ensure proposal handles Mike's scenario where tag value to branch mapping is not 1-1.
05/04: Discussed Mike's review comments and Suman's concerns. Agreed that name should be elementID, should be a single DFDL String Literal value, and that matching of choiceBranchRef expression result should only be against elementID to avoid QName v String confusion. Steve to recirculate with a schema example.
17/04: Closed. Discussion on whether the choiceBranchRef expression should retiurn xs:string or something else. Agreed on xs:string. Discussed whether elemenID should be a pure xs:string or a DFDL String Literal. For consistency with other DFDL properties it should be a string literal, but raw byte entities and character classes should be disallowed to avoid complications. Discussed scope of uniqueness of elementIDs. Agreed that uniqueness is both local to a choice, and across all global elements in the same namespace (the latter is not strictly needed right now but accommodates any future addition of xs:any). Agreed that elementID should be on global element, local element, and element ref (in which case it overrides any elementId on the global element, which is ok as the property does not follow the usual scoping rules). Errata taken.

Regards

Steve Hanson
Architect, IBM Data Format Description Language (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-- dfdl-wg mailing list dfdl-wg@ogf.org
https://www.ogf.org/mailman/listinfo/dfdl-wg

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-- dfdl-wg mailing list dfdl-wg@ogf.orghttps://www.ogf.org/mailman/listinfo/dfdl-wg -- dfdl-wg mailing list dfdl-wg@ogf.org https://www.ogf.org/mailman/listinfo/dfdl-wg

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