RE: [wsrf] Identifying WS-Resources: ReferenceProperties or ReferenceParameters?

["Djaoui, A (Abdeslem) " <A.Djaoui@rl.ac.uk>]

  Here is an extract from an article

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnwebsrv/html/introwsa.asp

than throws some light on when to use reference properties and reference parameters.

 

"The distinction between reference properties and reference parameters is in how they relate to a service's metadata. The policy and contract of a Web service is based on its base address and reference properties only. Typically, the base address and reference properties identify a given deployed service and the reference parameters are used to identify specific resources that are managed by that service.

 

There are many uses for reference properties. Two simple examples are classes of service and private entity identifiers. In the class of service example, reference properties may be used to differentiate between a Web service for standard customers and one for "gold" customers that provides a higher quality of service and enhanced capabilities, logically forming two different endpoints. Properties such as these are set only once in a session and then reused throughout the rest of the interaction.

An example of a second kind of use of a reference property is a mechanism to identify a customer in a manner private to the originating system.

A combination of these two types of reference properties could enable efficient message dispatch to the appropriate collection of servers and efficiently finding the application state that relates to a particular user. These examples also show how data that refers to instances of services and data that refers to instances of users can be represented in reference properties.

 

Two kinds of uses for reference parameters are infrastructural and application-level. An infrastructural example of a reference parameter can be a transaction/enlistment ID sent to a Transaction Processing monitor. In a book-purchase scenario, the ISBN number of a book can be an application-level example of a reference parameter."

-----Original Message-----
From: A Djaoui [mailto:a.djaoui@rl.ac.uk]
Sent: 13 August 2004 15:18
To: Steve Graham
Cc: Anish Karmarkar; Ugo Corda; wsn@lists.oasis-open.org; wsrf@lists.oasis-open.org
Subject: [wsrf] Identifying WS-Resources: ReferenceProperties or ReferenceParameters?

Hi Steve

I copied and pasted into a new thread since it looks this topic belongs on its own.

Steve Graham wrote:

Hi Abdeslem:


"Djaoui, A (Abdeslem) " <A.Djaoui@rl.ac.uk> wrote on 08/13/2004 07:34:34 AM:


> The introduction of Reference Parameters and the clarification on EPR comparison
> will benefit WSRF and help eradicate some of the question on how WS-addressing is
> used in WSRF. I never was comfortable with the way ReferenceProperties were used to
> identify WS-Resources. Reference Parameters seem to be more appropriate for that.
This is where we need further debate.
First, the EPR comparison section is somewhat helpful, but not terribly so.  For example,
it says nothing on reasoning about EPRs that are different. It is quite possible that
two EPRs differ, but still refer to the same resource. This situation is much more interesting
and happens quite a bit in systems management scenarios.  This is where the heart of
the matter actually lies.

Now, on the preference for Ref Parms to identify (disambiguate) resources, I am not sure
that is the right approach.
The WS-Addressing (Aug 2004) spec says (section 2.1):
[reference properties] : xs:any (0..unbounded).
A reference may contain a number of individual properties that are required to identify the entity or resource being conveyed.
So, (avoiding the grumbling about the use of the word identify) the spec suggests Ref Props,
not Ref Parms, are more appropriate for the sorts of things we are doing in WSRF.

sgg

Isn't this then in contradiction with the new WS-Addressing spec that suggests "A consuming application should assume that different XML schema, WSDL definitions and policies apply to endpoint references whose address or reference properties differ"? The way it is used now, we have  different referenceproperties associated with the same schema, wsdl and policy.

I concluded from the above statement that referenceproperties are used to allow the use of the same address by many different services (endpoints) (potentially different in schema, wsdl or policy). An example is a load balancing service that is a front for a server farm where different requests are routed to different machines depending on their policy requirements for example.
Now where does the reference parameters come in.
The spec says

[reference parameters] : xs:any (0..unbounded).
A reference may contain a number of individual parameters which are associated with the endpoint to facilitate a particular interaction

Each enpoint in the server farm can additionally use reference parameters to identify/disabiguatre WS-resources (subscriptions for example). So we have some sort of two level referencing. The first allows the use of one adress by many endpoints and the second allows the use of one endpoint by many ws-resources.

Abdeslem
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