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Re: Issue 6712 Discussion and Proposal

From: Doug Davis <dug@us.ibm.com>
Date: Thu, 28 May 2009 18:29:55 -0600
To: Gilbert Pilz <gilbert.pilz@oracle.com>
Cc: David Snelling <David.Snelling@UK.Fujitsu.com>, public-ws-resource-access@w3.org, public-ws-resource-access-request@w3.org
Message-ID: <OF3AD1C835.FA7D9E60-ON852575C5.00020229-852575C5.0002C15E@us.ibm.com>
That's right.  Since Transfer itself doesn't define any "instructions" 
(aka extensions) to go into the Create then the default case is the one 
where the XML represents the literal representation of the resource.  And 
since the spec itself calls out the use of instructions (aka defines the 
extension point) it must provide a means for an implementation to know 
when those extensions are being used - like we cleared up in [1].  But 
Dave is also correct that one option is to simply remove this extension 
point.  Those really are the only two options I see.

[1] http://www.w3.org/Bugs/Public/show_bug.cgi?id=6594

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.



Gilbert Pilz <gilbert.pilz@oracle.com> 
Sent by: public-ws-resource-access-request@w3.org
05/28/2009 07:23 PM

To
David Snelling <David.Snelling@UK.Fujitsu.com>
cc
public-ws-resource-access@w3.org
Subject
Re: Issue 6712 Discussion and Proposal






Dave,

W/respect to (d) it seems to me that the client can always turn around and 
do a Get on /wst:CreateResponse/wst:ResourceCreated and check to see if 
what got created was what it expected but this seems like an awfully 
inefficient and error prone way of solving this problem.

I agree with you about the @Dialect attribute. I think it is the cleanest 
way to solve this problem. It should also be accompanied by a class of 
nested policy assertions that the resource manager can use to advertise 
which dialects it supports. Since @Dialect and these policy assertions are 
optional, the base case collapses to your solution (a), which is to use 
the 'literal resource representation'.

- gp

On 5/11/2009 2:16 AM, David Snelling wrote: 
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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