Proposal for i008

[Tom Rutt <tom@coastin.com>]

Discussion around Issue 008: Granularity of policy attachment

For this discussion lets investigate the potential attachment of policy 
at a finer level than enpoint-subject.

Assume a default semantics associated with attaching policy at the 
operation level would be such that they apply only to the input message 
of that operation. There may be some benefit in resource utilization for 
an RMD, if it could support different DA levels for each operation 
supported by that endpoint. However this would require multiple 
sequences to be set up between the source and destination, one for each 
level of DA required (even thought the protocol is the same on each 
sequence, the actions of the RMD may be different due to DA requirments, 
such as buffering messages while waiting for prior).

Since the protocol is the same on every reliabile messaging sequence, 
irregardless of the agreed destination DA level, there is no great 
benefit in having multiple sequences between the same source and 
destination in order to support differing DA levels for different 
operations.

The use case of the broker interface can be served by applying exactly 
once in order delivery assurance for each operation on that endpoint. 
The extra cost of buffering messages for ordered delivery, even when it 
is not required, will only come into play during times of message loss.

During normal circumstances there would actually be no extra resources 
required to support ordered exactly once delivery, since each message 
will be received in proper order.

If each operation on the endpoint is be given the same DA support for 
their input messages, the endpoint has to support the most stringent DA 
level requirement over that endpoint’s operations..

As a design principle, the most stringent DA level required over the 
endpoint’s operations should be attached to that endpoint’s wsdl 
description.

If this design principle is adhered to, the default semantics associated 
with the proposal for Issue 21 are sufficient.

Lets assume that the following default semantics apply:

As a default, when rm policy assertions are attached to a WSDL 
description only at endpoint subject level, the implied semantics for 
all operations served by that endpoint can be interpreted as:
• each of those operations require reliable delivery only for their 
input messages.
• client relevant policy types (such as retransmission interval) apply 
to the RMS invoking on that Endpoint,
• server relevant policy types (such as DA levels and Ack interval) 
apply to the RMD at the service Endpoint.

Supporting expression of reliability policy different for each operation 
of a WSDL defined endpoint, would require attaching RM policy at the 
operation-subject level.

Supporting the expression of reliability policy for the output message 
of a wsdl request/response operation would require attaching rm policy 
at the message-subject level.

Such fine grained policy attachments can be left as extension points to 
the specification..

Proposed text change for Issue 008:

Add the following text after the text added for resolution of Issue 021:

“
Attaching reliability policy to a wsdl description at a finer level than 
endpoint-subject level is outside the scope of this version of the 
specification. Such out-of-scope policy attachments are considered 
extension points.

“

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Tom Rutt	email: tom@coastin.com; trutt@us.fujitsu.com
Tel: +1 732 801 5744          Fax: +1 732 774 5133