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Re: Issue 6712 Discussion and Proposal

From: David Snelling <David.Snelling@UK.Fujitsu.com>
Date: Mon, 11 May 2009 10:16:43 +0100
Message-Id: <13ABC2E2-7AA1-4390-94AE-2A72D7E10249@UK.Fujitsu.com>
To: public-ws-resource-access@w3.org

Folks,

It is clear to me that there are 2 semantics inferred in the T-spec 
for create that a service may support.

1) Make the payload the resource.

2) Use the payload in some way to make the resource.

As Geoff pointed out the service gets to decide which it supports or 
if it supports both. The spec is not even clear which is the default 
mode, so a client should consult a policy framework before proceeding. 
So we at least need to define a pair of URIs to use in a policy 
framework. As it stands the service may behave contrary to the 
client's assumption and the client will remain totally unaware of what 
semantic the service acted on.

I prefer the Dialect proposal, but I see a couple of other solutions. 
a) We could mandate a single semantic only, probably (1) above. b) We 
could allow both but a service MUST advertise which it supports in a 
policy framework. c) Add another version of the create operation, d) 
Mandate that the service always send back the resulting 
representation, so the client can check it and retry if the result is 
not what was expected.

On 07 May 2009, at 14:20, Doug Davis wrote:

>
> Geoff,
>   I forgot to mention that your solution actually doesn't work.  As 
> a service there are two types of Creates I might support (both legal 
> and advocated in the T spec):
> 1) Create where I pass in the xml representation as a child of the 
> Create
> 2) an 'instruction based' Create where the QName of the Create tells 
> me the instruction
> Obviously the QName of the child element in case #2 is not defined 
> by T so it will be service specific.  However, case #1 is something 
> that should work across all implementations of Transfer.  As a 
> service provider if I want to offer up both, your solution would not 
> work for me.  You're asking me to remove case #1 and make my 
> implementation totally non-interoperable.  Yes, clearly, case #2 
> will only be interoperable with other endpoints that know about my 
> service specific QName and that's ok.  However, what's not ok is for 
> me to have to remove case #1 because that's the baseline for interop 
> that I need to ensure the broadest support.  So, in terms of "bad 
> architectural decisions" that one would be pretty high on my list.
>
> thanks
> -Doug
> ______________________________________________________
> STSM |  Standards Architect  |  IBM Software Group
> (919) 254-6905  |  IBM 444-6905  |  dug@us.ibm.com
> The more I'm around some people, the more I like my dog.
>
>
> Doug Davis/Raleigh/IBM@IBMUS
> Sent by: public-ws-resource-access-request@w3.org
> 05/06/2009 09:07 PM
>
> To
> public-ws-resource-access@w3.org
> cc
> Subject
> RE: Issue 6712 Discussion and Proposal
>
>
>
>
>
>
> I actually agree.  The WS-Transfer team that wrote the spec made a 
> very bad architecture decision by explicitly saying that something 
> can be done but not provide a way for it to actually happen.  Glad 
> we can finally agree on something.
>
> I accept your modified proposal to rename the attribute.
>
> thanks
> -Doug
> ______________________________________________________
> STSM |  Standards Architect  |  IBM Software Group
> (919) 254-6905  |  IBM 444-6905  |  dug@us.ibm.com
> The more I'm around some people, the more I like my dog.
>
> Geoff Bullen <Geoff.Bullen@microsoft.com>
> 05/06/2009 08:56 PM
>
>
> To
> Doug Davis/Raleigh/IBM@IBMUS, "public-ws-resource-access@w3.org" <public-ws-resource-access@w3.org
> >
> cc
> Subject
> RE: Issue 6712 Discussion and Proposal
>
>
>
>
>
>
>
> Doug,
> >From the email below, we assume that:
>
> <Body>
> <doit xmlns="urn:foo"/>
> </Body>
>
> Actually means:
>
> [Body]
> <create>
> <Body>
> <doit xmlns="urn:foo"/>
> </Body>
>            </create>
>
> The server is in complete control of definition and contents of the 
> first child element, in this case an element called “body”.
>
> The line of reasoning followed by IBM in the mail thread below seems 
> to be that the Server implementer deliberately chooses to use the 
> “body” element above, so that the Server code cannot tell the 
> difference between the incoming elements in a Create message.  The 
> implementer does this rather than choosing a different strategy such 
> as the one we suggest below, where the Server could easily tell the 
> difference.
>
> This same line of reasoning seems to continue that, because it is 
> possible for the Server implementer to make such a really bad 
> architectural decision, the WG should accommodate this use case by 
> creating an brand new attribute in the Transfer spec (just for 
> Create) to allow the client the specify which one is really meant.  
> But, of course, the Server implementer, having worked out that it is 
> a really bad architecture, now has to also add new Server code to 
> support this new attribute in order to “hack the fix in”, rather 
> than simply add code to correct the actual architectural issue.
>
> Perhaps we should call this new attribute <create 
> usingReallyBadImplementation=”1”> ?
>
> --Geoff
>
>
> From: public-ws-resource-access-request@w3.org [mailto:public-ws-resource-access-request@w3.org
> ] On Behalf Of Doug Davis
> Sent: Wednesday, May 06, 2009 3:45 PM
> To: public-ws-resource-access@w3.org
> Subject: RE: Issue 6712 Discussion and Proposal
>
>
> The server. If the server supports both (meaning it accept both an 
> instruction and storing of xs:any) and the Body looks like:
> <Body>
> <doit xmlns="urn:foo"/>
> </Body>
>
> is it a chunk of XML or is it the "doit" instruction?  It (the 
> server) can't tell.
>
> thanks
> -Doug
> ______________________________________________________
> STSM |  Standards Architect  |  IBM Software Group
> (919) 254-6905  |  IBM 444-6905  |  dug@us.ibm.com
> The more I'm around some people, the more I like my dog.
> Geoff Bullen <Geoff.Bullen@microsoft.com>
> Sent by: public-ws-resource-access-request@w3.org
> 05/06/2009 06:29 PM
>
>
> To
> Doug Davis/Raleigh/IBM@IBMUS, "public-ws-resource-access@w3.org" <public-ws-resource-access@w3.org
> >
> cc
> Subject
> RE: Issue 6712 Discussion and Proposal
>
>
>
>
>
>
>
>
>
>
> > … but doesn't provide a way to unambiguously know which it is.
>
> Doug,
> Who is it that has to unambiguously know?  The client?  The server?  
> Each of these does unambiguously know.
> --Geoff
>
> From: public-ws-resource-access-request@w3.org [mailto:public-ws-resource-access-request@w3.org
> ] On Behalf Of Doug Davis
> Sent: Wednesday, May 06, 2009 3:22 PM
> To: public-ws-resource-access@w3.org
> Subject: RE: Issue 6712 Discussion and Proposal
>
>
> Geoff,
> that solution, while technically possible, implies that we can not 
> use Transfer the way it was designed.  It says:
>
> [Body]/wst:Create
>  If this REQUIRED element contains children then the first child 
> MUST be the literal resource representation, a representation of the 
> constructor for the resource, or other instructions for creating the 
> resource.
>
> It allows for the immediate child of the Create element to be either 
> the XML or an instruction, but doesn't provide a way to 
> unambiguously know which it is.
>
> thanks
> -Doug
> ______________________________________________________
> STSM |  Standards Architect  |  IBM Software Group
> (919) 254-6905  |  IBM 444-6905  |  dug@us.ibm.com
> The more I'm around some people, the more I like my dog.
>
> Geoff Bullen <Geoff.Bullen@microsoft.com>
> 05/06/2009 05:56 PM
>
>
>
> To
> Doug Davis/Raleigh/IBM@IBMUS
> cc
> "public-ws-resource-access@w3.org" <public-ws-resource-
> access@w3.org>, "public-ws-resource-access-request@w3.org" <public-ws-resource-access-request@w3.org
> >
> Subject
> RE: Issue 6712 Discussion and Proposal
>
>
>
>
>
>
>
>
>
>
>
>
>
> > If I have a transfer service that is storing a blob of xml in a DB 
> and it allows the XML to be anything - how do I know if the client 
> meant for it to be stored "as is" or for the QName to indicate an 
> instruction?  Assuming of course that the service supports 
> instructions as well.
>
> Doug,
> The Transfer service is in control, it knows its own content, and it 
> knows the difference between blobs and instructions.  If the 
> situation quoted above arises for a particular Transfer service, 
> then it could easily distinguish between blobs and instructions 
> using some strategy such as:
>
> Request from client to transfer service to create a blob:
> [body]
> <create>
>   <blob>
>      … contents of blob to be stored in DB (any XML can be put here) …
>   </blob>
> </create>
>
> Request from client to transfer service to create resource using a 
> set of rules:
> [body]
> <create>
>   <MyInstructions>
>      … set of instructions defined here (only instruction specific 
> XML can be put here) …
>   </MyInstructions>
> </create>
>
>
> From: Doug Davis [mailto:dug@us.ibm.com]
> Sent: Wednesday, May 06, 2009 7:54 AM
> To: Geoff Bullen
> Cc: public-ws-resource-access@w3.org; public-ws-resource-access-request@w3.org
> Subject: RE: Issue 6712 Discussion and Proposal
>
>
> > Even HTTP itself has a "message format" flag - its called "Content-
> Type".
>
> Doug, it is good that you are wanting to model Transfer after HTTP.  
> The Content-Type field is used to indicate the media type of the 
> underlying data. The media type of a SOAP message is well defined. 
> The type of the first child element of a Create message can be 
> inferred from the QName of the first child element.
>
> I wouldn't assume that ;-)  I only mentioned it because I know you 
> like to make the comparison.  I actually am not fond of it because 
> you're being very selective about which bits of HTTP to mimic - 
> basically just the ones you like and ignoring the others.  For 
> example, HTTP has the notion of fragments - two different ways (# in 
> the URL and Range headers).
> As for the QName... see below.
>
> > the QName of the child can tell you most everything you need to 
> know - however, the one case of the resource being an xs:any is 
> still left ambiguous
>
> Why is this ambiguous and to whom is it ambiguous?  Even though it 
> has been defined as an xs:any in the Transfer schema, it is clearly 
> defined by the Service that implements it (this is stated by the 
> spec).  It is not ambiguous to the Service at all, nor the client, 
> since the client knows what the Service demands.
>
> If I have a transfer service that is storing a blob of xml in a DB 
> and it allows the XML to be anything - how do I know if the client 
> meant for it to be stored "as is" or for the QName to indicate an 
> instruction?  Assuming of course that the service supports 
> instructions as well.
>
> thanks
> -Doug
> ______________________________________________________
> STSM |  Standards Architect  |  IBM Software Group
> (919) 254-6905  |  IBM 444-6905  |  dug@us.ibm.com
> The more I'm around some people, the more I like my dog.
>
> Geoff Bullen <Geoff.Bullen@microsoft.com>
> 05/06/2009 10:39 AM
>
>
>
>
>
> To
> Doug Davis/Raleigh/IBM@IBMUS
> cc
> "public-ws-resource-access@w3.org" <public-ws-resource-
> access@w3.org>, "public-ws-resource-access-request@w3.org" <public-ws-resource-access-request@w3.org
> >
> Subject
> RE: Issue 6712 Discussion and Proposal
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> > Even HTTP itself has a "message format" flag - its called "Content-
> Type".
>
> Doug, it is good that you are wanting to model Transfer after HTTP.  
> The Content-Type field is used to indicate the media type of the 
> underlying data. The media type of a SOAP message is well defined. 
> The type of the first child element of a Create message can be 
> inferred from the QName of the first child element.
>
> > the QName of the child can tell you most everything you need to 
> know - however, the one case of the resource being an xs:any is 
> still left ambiguous
>
> Why is this ambiguous and to whom is it ambiguous?  Even though it 
> has been defined as an xs:any in the Transfer schema, it is clearly 
> defined by the Service that implements it (this is stated by the 
> spec).  It is not ambiguous to the Service at all, nor the client, 
> since the client knows what the Service demands.
>
> --Geoff
>
>
> From: Doug Davis [mailto:dug@us.ibm.com]
> Sent: Tuesday, May 05, 2009 3:11 PM
> To: Geoff Bullen
> Cc: public-ws-resource-access@w3.org; public-ws-resource-access-request@w3.org
> Subject: Re: Issue 6712 Discussion and Proposal
>
>
> This does not address the usecase that I'm worried about [1] nor the 
> issue.  Even HTTP itself has a "message format" flag - its called 
> "Content-Type".  In cases where there are multiple ways to interpret 
> the data (which is something that Transfer itself promotes) it only 
> seems logical for Transfer to provide the mechanism by which users 
> of the spec can do that.  We don't need to specify much since the 
> QName of the child can tell you most everything you need to know - 
> however, the one case of the resource being an xs:any is still left 
> ambiguous.
>
> [1] http://lists.w3.org/Archives/Public/public-ws-resource-access/2009Apr/0142.html
>
> thanks
> -Doug
> ______________________________________________________
> STSM |  Standards Architect  |  IBM Software Group
> (919) 254-6905  |  IBM 444-6905  |  dug@us.ibm.com
> The more I'm around some people, the more I like my dog.
>
> Geoff Bullen <Geoff.Bullen@microsoft.com>
> Sent by: public-ws-resource-access-request@w3.org
> 05/05/2009 01:05 PM
>
>
>
>
>
>
>
> To
> "public-ws-resource-access@w3.org" <public-ws-resource-access@w3.org>
> cc
> Subject
> Issue 6712 Discussion and Proposal
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> After further consideration of Issue 6712 (http://www.w3.org/Bugs/Public/show_bug.cgi?id=6712

> ), which concerns the Create message in Transfer, we don’t really 
> think it matters if the spec is inferring that a given service or 
> resource can support more than one format of Create Message or not.  
> First, a few assumptions:
> a)     Each Service is ultimately responsible for deciding what type 
> and format of information is sent in a Create message.
> b)     Each Service will define its own set of “creation rules” (if 
> any) which will be used to create its resources.  That is, the WG 
> will not define some common creation rules language that will be 
> used by all resources.  A Service may even support more than one 
> format of creation rules if it wants to.
>
> Since the service is responsible for providing the definition of 
> each Create message format it supports, it is also responsible for 
> demining how it will tell the difference between those multiple 
> formats when they occur in a Create message.   One way that the 
> service might easily do this is as follows:
>
> Defining the literal Resource to create:
> [Header]
>           <wsam:Action>…/ws-tra/Create</wsam:Action>
> [Body]
> <Create>
>           <xxx:MyResource>
>                          Resource Definition here
>           </xxx:MyResource>
> </Create>
>
> Defining a set of rules to create a Resource:
> [Header]
>           <wsam:Action>…/ws-tra/Create</wsam:Action>
> [Body]
> <Create>
>           <xxx:MyRules>
>                          Rules here
>           </xxx:MyRules>
> </Create>
>
> In the end, there is no real difference between these two examples. 
> It is not clear then what the value is in providing a means within 
> the protocol for determining the message format (e.g. a resource or 
> rule flag).  Since the resource (service) is responsible for the 
> definition of both “MyResource” and “MyRules” there is literally 
> nothing extra in the Transfer protocol that is needed to help the 
> resource understand the type of “instructions” it has been sent in a 
> Create message.  To add some flag to the Transfer protocol seems 
> purely redundant and unnecessary.
>
> Based on the feedback from the WG, it does seem like some clarifying 
> text is required, we propose:
>
> [Body]/wst:Create
>
> This REQUIRED element MAY contain zero or more child elements. If 
> this element does not contain a child element then the resource will 
> be created using default values. The first child element, if 
> present, is service-specific (or the interpretation of the first 
> child element is defined by the resource to which the create message 
> is addressed) and MUST be the literal resource representation, a 
> representation of the constructor for the resource, or other 
> instructions for creating the resource. Additional extension 
> elements MAY be included only after the mandated first child element.
>
> --Geoff
>
>
>
>

Take care:

     Dr. David Snelling < David . Snelling . UK . Fujitsu . com >
     Fujitsu Laboratories of Europe Limited
     Hayes Park Central
     Hayes End Road
     Hayes, Middlesex  UB4 8FE
     Reg. No. 4153469

     +44-7590-293439 (Mobile)






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