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Subject: Re: [wsrf] issue 127 - : MUST use RAP?
The WS-RAP text regarding the requirement that a resource resource
identifier MUST appear as part of the message is important as is the
requirement that WS-Resources MUST use WS-RAP when implementing the WS-RF
protocol messages. This is the normative means by which such protocol
messages can be interoperably targetted at specific WS-Resources (i.e
endpoints with specific RPDoc instances), since the protocol messages do
not themselves explicitly pass resource identifiers. From an
interoperability perspective, the WS-Resource spec defers to the
application and its compliance with WS-Addressing to define how and where
in the message that identifier appears and the form that the identifier
takes.
We have discussed the so-called "singleton resource" case before. In this
case the address of the WS-Resource is sufficient to identify the resource
and so the resource identifier may appear as part of (or as the entirety
of) the wsa:Address element information item of the endpoint reference, as
mentioned in section 2.4 of WS-Resource. The resource identifier (i.e the
information required to distinguish the resource) still appears in the
message in the wsa:Address serialization - for example, in a SOAP message
this is the wsa:To header. Earlier drafts of the WS-Resource specification
(prior to the Oct 2004 F2F) had a specific example of such an "embodiment"
for the singleton pattern. I think it would be useful to resurrect that
information in the AppNotes to specifically deal with the singleton pattern
case, but if we do that it should be a separate consideration from issue
127.
Regards,
Ian Robinson
STSM, WebSphere Messaging and Transactions Architect
IBM Hursley Lab, UK
ian_robinson@uk.ibm.com
David Snelling
<David.Snelling@U
K.Fujitsu.com> To
WSRF <wsrf@lists.oasis-open.org>
07/08/2005 20:02 cc
Subject
Re: [wsrf] issue 127 - : MUST use
RAP?
Folks,
Ian's proposal I believe addresses the issue a stated. We can go with
it but I think we should look at a few options before jumping in.
My understanding is that, when reduced to its most fundamental, the
only normative aspect of the WS-Resource Access Pattern is that the
identification of the target resource MUST appear in the *message*.
Note that since the resource (or a factory for it) provides the
reference to the resource, this normative statement is not strictly
required for interoperability. For example, if as a WS-Resource I
provide only a URL and do not require my identifier to appear in the
*message*, any client with my WSDL and this URL can contact me. I don't
see an interoperability need for the identifier to appear in the
*message*. The address alone should be sufficient.
We should consider dropping this requirement, as it would allow the
WSRF specs to compose more easily with other specifications.
Note: I am not opposed to Ian's proposal, I just would like to know it
it is actually required.
Thoughts?
On 5 Aug 2005, at 21:49, Ian Robinson wrote:
>
>
>
>
> This pulic review issue states:
> Line 372 (and others) says, "The GetResourcePropertyDocument request
> message MUST follow the WS-Resource Access Pattern." I'm not clear what
> requirement this normative MUST imposes on the implementer. RFC 2119
> says
> keywords "MUST only be used where it is actually required for
> interoperation or to limit behavior which has potential for causing
> harm
> (e.g., limiting retransmissions). For example, they must not be used
> to try
> to impose a particular method on implementers where the method is not
> required for interoperability." I assume, then, that the requirement to
> follow the WS-Resource Access Pattern has something to do with
> interoperability. But the definition in WS-Resource isn't much help
> when it
> says, "An identifier of the resource MUST appear as part of any
> message to
> a WS-Resource to allow the WS-Resource to disambiguate the resource
> targeted by the message. We refer to this pattern of access as the
> 'WS-Resource Access Pattern'." Would it be possible to spell out more
> clearly what an implementer needs to do to satisfy the interop
> requirements
> of WS-RAP?
>
>
>
> Use of the WS-Resource access pattern is a requirement for
> interoperability
> but, since we went back to a single embodiment, the description of what
> WS-RAP implies now looks a little obtuse. I propose this issue be
> resolved
> by retaining the MUST in WSRF-RP and by re-establishing a little of the
> text we lost from WS-Resource when removing the embodiments.
>
> Specifically, replace the bullet at line 127 of WS-Resource with:
>
> · "An identifier of the resource MUST be represented in any
> reference
> to a WS-Resource and MUST appear as part of any message to a
> WS-Resource to
> allow the WS-Resource to disambiguate the resource targeted by the
> message.
> We refer to this pattern of access as the “WS-Resource Access Pattern”
> (WS-RAP). The precise location of the resource identifier in a message
> to a
> WS-Resource depends on how the identifier is represented in the
> WS-Resource
> reference used to access the WS-Resource and also on the
> transport-specific
> bindings used to serialize the message."
>
> and update the definition of WS-Resource reference to:
>
> "A WS-Resource reference (or just reference) is a construct through
> which a
> single WS-Resource can be accessed. It is represented by an endpoint
> reference, or more precisely an XML element whose type is, or is
> derived
> (by extension) from the complexType named EndpointReferenceType
> defined by
> the [WS-Addressing] specification. The address of the Web service
> endpoint
> part of the WS-Resource is contained in the wsa:Address element
> information
> item of the endpoint reference. The resource identifier MUST appear
> either
> in the contents of the wsa:ReferenceParameter element information item
> of
> the endpoint reference or embedded as part of the wsa:Address element
> information item of the endpoint reference. In a message that is
> conformant
> to the WS-Resource Access Pattern the resource identifier of the
> resource
> must appear in the message according to binding-specific rules
> outlined in
> WS-Addressing. For example, in the SOAP binding defined by
> WS-Addressing,
> the Web service endpoint address is contained in the wsa:Address
> element
> information item in the endpoint reference and appears in the message
> as
> the contents of the wsa:To SOAP header, and each direct child element
> information item (if any) of the wsa:ReferenceParameter element
> information
> item appears in the message as a separate SOAP header.
>
>
> For a given resource identifier there may be many references. The way
> two
> references are compared for equality is implementation-specific and not
> defined by this specification."
>
>
>
>
>
> Attached is a version of WS-Resource with change tracking to
> illustrate the
> changes:
>
>
> (See attached file: wsrf-ws_resource-1.2-spec-issue127.doc)
>
>
>
> Regards,
> Ian<wsrf-ws_resource-1.2-spec-issue127.doc>
--
Take care:
Dr. David Snelling < David . Snelling . UK . Fujitsu . com >
Fujitsu Laboratories of Europe
Hayes Park Central
Hayes End Road
Hayes, Middlesex UB4 8FE
+44-208-606-4649 (Office)
+44-208-606-4539 (Fax)
+44-7768-807526 (Mobile)
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