[DFDL-WG] Direct dispatch choice clarifications (action 219)
Tim Kimber
KIMBERT at uk.ibm.com
Mon Sep 2 17:55:51 EDT 2013
I can see where you're going with this, but I don't find either option
very intuitive. My preference would be 'choiceDispatchKey' on the choice
group and 'choiceBranchKey' on the choice branch. I'm not too worried
about using the word 'key' - I don't think users will get confused by it
when it is combined with 'dispatch' and 'branch' in the property names.
regards,
Tim Kimber, DFDL Team,
Hursley, UK
Internet: kimbert at uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
From: Steve Hanson/UK/IBM at IBMGB
To: dfdl-wg at ogf.org,
Date: 02/09/2013 18:24
Subject: Re: [DFDL-WG] Direct dispatch choice clarifications
(action 219)
Sent by: dfdl-wg-bounces at ogf.org
I am leaning away from the use of 'key' because XML schema has xs:key and
xs:keyRef components and people might think they are related somehow.
I think a good analogy is with the switch statement in languages.
Suggestions:
1) 'dfdl:switch' on the choice and 'dfdl:case' or 'dfdl:switchCase' on the
element - con is clash with dfdl:ignoreCase.
2) 'dfdl:switch' on the choice and 'dfdl:switchWhen'' on the element.
Regards
Steve Hanson
Architect, IBM 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: Steve Hanson/UK/IBM
To: Mike Beckerle <mbeckerle.dfdl at gmail.com>,
Date: 30/08/2013 15:06
Subject: Re: [DFDL-WG] Direct dispatch choice clarifications
(action 219)
Updated errata 3.15 to answer the open comments against that errata. Also
updated errata 2.126 to add the properties to the list of
non-representation properties.
Regards
Steve Hanson
Architect, IBM 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: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: Steve Hanson/UK/IBM at IBMGB,
Date: 30/08/2013 00:10
Subject: Re: [DFDL-WG] Direct dispatch choice clarifications
(action 219)
Updated errata 3.15, so please review that in the errata doc also.
Corresponding changes are marked with OPEN bubbles, except in the Property
precedence part. (Did those by global search/replace).
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, Aug 21, 2013 at 12:21 PM, Steve Hanson <smh at uk.ibm.com> wrote:
Discussed this some more on the WG call.
The original proposal from Steve envisaged a single property,
choiceBranchRef, which was an expression that returned a QName. The
attraction of this is that no property is needed on the element. It
supports the use case where the 'tag' in the data corresponds closely to
the element name, which is the case for something like SWIFT. Further, it
is easy to extend this idea to xs:any wildcards in a future DFDL release.
However if the 'tag' is very different from the element name then the
expression can become a big 'if' statement and some of the performance
benefit is lost. Hence the current proposal for choiceBranchRef expression
returning a simple string, and the need for a property on elements. This
gets us into a problem with global elements and uniqueness.
What is needed for DFDL 1.0 is a mechanism that gives good performance for
the known use cases, and is local to a choice, and does not preclude the
provision of a QName based solution in a future DFDL release. What we have
now is a halfway house. So the following is proposed:
Change the name choiceBranchRef to choiceKey (or choiceTag or TBD).
Note that the use of 'Ref' is dropped as that implies QName in all other
properties that use 'Ref'.
Change the name elementID to branchKey (or branchTag or TBD).
Disallow branchKey on a global element, so it is allowed only on local
elements and element refs.
This removes the need for the special rule about choiceBranchKey on
element ref overriding that on a global element.
The mechanism is now entirely local to a choice, and will not clash with
any future QName based scheme.
Regards
Steve Hanson
Architect, IBM 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: Steve Hanson/UK/IBM
To: dfdl-wg at ogf.org,
Date: 19/08/2013 15:07
Subject: Fw: [DFDL-WG] Direct dispatch choice clarifications
OK, I can go with changing elementID to something less suggestive of XSDL.
I've spoken with Suman and changing it is not a big deal in our model.
Regards
Steve Hanson
Architect, IBM Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
----- Forwarded by Steve Hanson/UK/IBM on 19/08/2013 14:35 -----
From: Tim Kimber/UK/IBM at IBMGB
To: dfdl-wg at ogf.org,
Date: 17/08/2013 11:51
Subject: Re: [DFDL-WG] Direct dispatch choice clarifications
Sent by: dfdl-wg-bounces at ogf.org
I'm in general agreement with that.
Just to avoid any possible confusion:
I think the important thing is to stop thinking of elementID as any sort
of XSD/DFDL language ID. It is not. It is a DFDL String Literal, meaning
but it must describe a simple string value and it's value is matched
against the return value of the choiceBranchRef expression. data.
regards,
Tim Kimber, DFDL Team,
Hursley, UK
Internet: kimbert at uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: Steve Hanson/UK/IBM at IBMGB,
Cc: "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>, "dfdl-wg-bounces at ogf.org"
<dfdl-wg-bounces at ogf.org>, Tim Kimber/UK/IBM at IBMGB
Date: 16/08/2013 18:54
Subject: Re: [DFDL-WG] Direct dispatch choice clarifications
I am ok with leaving the name elementID as is purely due to our schedule.
However, I really do think it would be good to change it now.
I think it is that name which is creating all the confusion, and we really
ought to be more careful.
I think the important thing is to stop thinking of elementID as any sort
of XSD/DFDL language ID. It is not. It is a DFDL String Literal, meaning
it's value is matched against data.
For example: It could be dfdl:elementID="%NUL;%NUL;%NUL;%NUL;" meaning 4
null chars. So that when the choiceBranchRef="{ ../hdr/tag }" evaluates to
a 4 character string, then if they are all nul the branch is taken by
direct dispatch. This character NUL isn't allowed in any namespaced
identifiers in XSD or DFDL. It isn't even allowed in XML.
If I had dfdl:termnator="%NUL;" you wouldn't ask "what namespace is that
%NUL; in?"
So I think elementID is not, in anyway, a namespace-qualified identifier
any more than a delimiter is.
So I think uniqueness of the elementID within the alternatives of a choice
should be the only requirement. This stuff about unique within a namespace
if on a global element should be dropped.
The other argument for changing the name from elementID to something more
choice-dispatch specific is that this workgroup seems to be speculating
about using elementID for some sort of future wildcard-oriented feature. I
think we should reserve names we want for that future by NOT using them
now. If we use them now, we lock down part of the semantics in a way which
may just not work properly with some future addition to DFDL. Do we really
want elementID which is about direct dispatch choices but is not an
identifier, and then in the future have dfdl:wildcardElementID which is
about wildcards and IS an identifier. That's a mess.
If you think elementID is a really good name for some future wildcard
feature, then you should be advocating to NOT use it now for direct
dispatch choices. That is, unless you have a complete design in mind for
the wildcard stuff and are confident that elementID can be overloaded in a
backward compatible way. I've seen nothing like this articulated.
...mike
On Fri, Aug 16, 2013 at 12:32 PM, Steve Hanson <smh at uk.ibm.com> wrote:
IBM has started to implement choiceBranchRef, in so far as the XML schemas
for DFDL have been updated to include elementID and we have regenerated
all our model code. I'd like to stick with elementID please.
Regards
Steve Hanson
Architect, IBM 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: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: Steve Hanson/UK/IBM at IBMGB,
Cc: Tim Kimber/UK/IBM at IBMGB, "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>, "
dfdl-wg-bounces at ogf.org" <dfdl-wg-bounces at ogf.org>
Date: 16/08/2013 17:09
Subject: Re: [DFDL-WG] Direct dispatch choice clarifications
I think we need to stay out of identifiers and namespaces and qnames for
this feature.
The elementID should have to be locally unique within the alternatives of
the choice that is dispatching to it. If that elementID lives on a global
element declaration, that means nothing at all alone. In the context of a
choice that has an element ref to that global element, then it has to be
unique within the arms of that choice.
This means it is possible to have two global element decls which have
elementID="X", and there is no conflict unless they are both used via
element refs from the same choice.
I think this handles every use case I know of. The "namespace" requirement
for elementID is only "unique within alternatives of a choice".
Since nobody has implemented this feature yet, I would posit that we
should change elementID to something less suggestive of an XSD
identifier/QName-ish thing. Such as choiceDispatchTag.
...mike
On Fri, Aug 16, 2013 at 5:18 AM, Steve Hanson <smh at uk.ibm.com> wrote:
You are right about the xs:QName constructor, it takes a string which is
prefix plus name. If we supplied a dfdl:QName constructor that took a URI
and a name, that would simplify things.
For example, the choiceBranchRef expression for SWIFT would be as below.
(The element name is always Document and the namespace is used to
distinguish the different messages).
{dfdl:QName(fn:concat(fn:concat('urn:swift:xsd:fin.',
/FinMessage/Block2/MessageType), ".2011"), 'Document')}
If we stick with elementID for DFDL 1.0, then I agree with your 3 bullets,
but not the defaulting to element name as it is setting a behaviour that
may not be where we want to go for 2.0.
Regards
Steve Hanson
Architect, IBM 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: Tim Kimber/UK/IBM at IBMGB
To: dfdl-wg at ogf.org,
Date: 15/08/2013 20:34
Subject: Re: [DFDL-WG] Direct dispatch choice clarifications
Sent by: dfdl-wg-bounces at ogf.org
The other problem with using a QName is that it involves using namespace
prefixes. That means that there needs to be a mapping between prefixes and
namespace URIs. I can see that getting very problematic if the choice
group is located in a different xsd from the global elements that it
references.
I think we should
- keep the elementID as a simple string
- insist that all branches of a choice have different elementIDs
- remove the global uniqueness constraint, for the reasons explained in
this email chain
I think it would be easier for modellers if the elementID defaulted to the
local name of the element. I understand that name clashes can, in
principle, occur. If users want to avoid that then they can be explicit
about elementIDs and they could even define a naming convention for their
elementIDs to make them look very much like QNames. Sounds like a lot of
work, but DFDL models that are complex enough to need that approach will
often be code-genned anyway.
regards,
Tim Kimber, DFDL Team,
Hursley, UK
Internet: kimbert at uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
From: Steve Hanson/UK/IBM at IBMGB
To: dfdl-wg at ogf.org,
Date: 15/08/2013 18:37
Subject: Re: [DFDL-WG] Direct dispatch choice clarifications
Sent by: dfdl-wg-bounces at ogf.org
The more I think it through, the more I see the use of a string elementID
(or local element name) causing problems when/if we extend to support
xs:any in the future. In my original proposal for direct dispatch choice
I proposed that choiceBranchRef returned a QName which therefore
automatically selected the element, and coped with any namespace issues.
The problem with QName though is that the expression to build it can
become a big case statement negating some of the performance gain, if
there is no automap way of getting from the 'tag' to the QName. Hence why
we introduced elementID.
Regards
Steve Hanson
Architect, IBM 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: Steve Hanson/UK/IBM
To: Suman Kalia <kalia at ca.ibm.com>,
Cc: dfdl-wg at ogf.org, dfdl-wg-bounces at ogf.org, Tim
Kimber/UK/IBM at IBMGB
Date: 15/08/2013 17:20
Subject: Re: [DFDL-WG] Direct dispatch choice clarifications
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 at uk.ibm.com
tel:+44-1962-815848
From: Suman Kalia <kalia at ca.ibm.com>
To: Tim Kimber/UK/IBM at IBMGB,
Cc: dfdl-wg at ogf.org, dfdl-wg-bounces at ogf.org
Date: 15/08/2013 15:31
Subject: Re: [DFDL-WG] Direct dispatch choice clarifications
Sent by: dfdl-wg-bounces at 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 at ca.ibm.com
For info on Message broker
http://www.ibm.com/developerworks/websphere/zones/businessintegration/wmb.html
From: Tim Kimber <KIMBERT at uk.ibm.com>
To: dfdl-wg at ogf.org,
Date: 08/15/2013 09:58 AM
Subject: Re: [DFDL-WG] Direct dispatch choice clarifications
Sent by: dfdl-wg-bounces at ogf.org
See comment in <TK> tags.
regards,
Tim Kimber, DFDL Team,
Hursley, UK
Internet: kimbert at uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
From: Steve Hanson/UK/IBM at IBMGB
To: dfdl-wg at ogf.org,
Date: 15/08/2013 12:57
Subject: [DFDL-WG] Direct dispatch choice clarifications
Sent by: dfdl-wg-bounces at 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 at uk.ibm.com
tel:+44-1962-815848
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www.tresys.com
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