W3C home > Mailing lists > Public > public-ws-resource-access@w3.org > May 2009

RE: Issue 6712 Discussion and Proposal

From: Geoff Bullen <Geoff.Bullen@microsoft.com>
Date: Thu, 7 May 2009 16:33:13 -0700
To: Doug Davis <dug@us.ibm.com>, "public-ws-resource-access@w3.org" <public-ws-resource-access@w3.org>
Message-ID: <5AAAA6322448AA41840FC4563A30D6E843A081CD6E@NA-EXMSG-C122.redmond.corp.microsoft.com>
Doug,

> 1) Create where I pass in the xml representation as a child of the Create

The spec uses the term "literal resource representation"

> 2) an 'instruction based' Create where the QName of the Create tells me the instruction

Actually, the spec does not talk about QName's at all, nor what their purpose is, this is just an implementation assumption that is being made here.

> 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.

There seems to be an assumption being made here that the Transfer specification in some way "defines" what the literal resource representation (case #1) actually looks like, and that therefore, if the first child element does not "conform" to this definition there is an interop issue.  It is our understanding that the literal resource representation (case #1) can be any XML representation, and is service specific (i.e. defined by the service), just as in case #2.  Can you please point to the normative language in Transfer that defines what a literal resource representation should look like?  Again, it is our understanding that:
<Resource>  ... definition... </Resource>
and
<MyWrapper> <Resource>  ... definition... </Resource> </MyWrapper>
are both valid resource representations.  Can you explain why the second example is NOT a valid resource representation?

> You're asking me to remove case #1 and make my implementation totally non-interoperable.

It is also unclear what is meant here by interoperable.  Can you please explain the scenario in which interop is broken?  That would help a great deal.  If this is such a major interop issue, we are surprised that Transfer has been implemented by so many and achieved such a high level of interop to date.  Perhaps there is a vital new interop example that needs to be added to everyone's test cases?

--Geoff


From: public-ws-resource-access-request@w3.org [mailto:public-ws-resource-access-request@w3.org] On Behalf Of Doug Davis
Sent: Thursday, May 07, 2009 6:20 AM
To: public-ws-resource-access@w3.org
Subject: RE: Issue 6712 Discussion and Proposal


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<mailto:dug@us.ibm.com>
The more I'm around some people, the more I like my dog.
Geoff Bullen <Geoff.Bullen@microsoft.com<mailto:Geoff.Bullen@microsoft.com>>

05/06/2009 10:39 AM






To

Doug Davis/Raleigh/IBM@IBMUS

cc

"public-ws-resource-access@w3.org<mailto:public-ws-resource-access@w3.org>" <public-ws-resource-access@w3.org<mailto:public-ws-resource-access@w3.org>>, "public-ws-resource-access-request@w3.org<mailto:public-ws-resource-access-request@w3.org>" <public-ws-resource-access-request@w3.org<mailto: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]<mailto:[mailto:dug@us.ibm.com]>
Sent: Tuesday, May 05, 2009 3:11 PM
To: Geoff Bullen
Cc: public-ws-resource-access@w3.org<mailto:public-ws-resource-access@w3.org>; public-ws-resource-access-request@w3.org<mailto: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<mailto:dug@us.ibm.com>
The more I'm around some people, the more I like my dog.
Geoff Bullen <Geoff.Bullen@microsoft.com<mailto:Geoff.Bullen@microsoft.com>>
Sent by: public-ws-resource-access-request@w3.org<mailto:public-ws-resource-access-request@w3.org>

05/05/2009 01:05 PM








To

"public-ws-resource-access@w3.org<mailto:public-ws-resource-access@w3.org>" <public-ws-resource-access@w3.org<mailto: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
Received on Thursday, 7 May 2009 23:34:00 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Saturday, 18 December 2010 18:17:59 GMT