RE: [ws-rx] Proposed NEW ISSUE: Alignment and Refinement of Definitions for Delivery Assurances

Title: RE: [ws-rx] Proposed NEW ISSUE: Alignment and Refinement of Definitions for Delivery Assurances

Tom:

Step #1 looks OK to me.

Step #2 I am not sure what we try to achieve here.

I see no harm having the DAs *defined*  as predicates, independently from the functions that support them. I have no issue with leaving out any mention of the protocol or other functions in these defs. If we try to identify RMS/RMD functions that support them, that may be useful as an implementation guide, but do they need to be part of the definition?

This said, I still think DAs could be defined more precisely - e.g. AtLeastOnce is vague as where the error should be raised - and whether these errors should translate into app notifications or some form of exposure to app (there does not seem to be any requirement here - yet this can be seen as part of the contract RMD-AD, and also maybe RMS-AS...)

Step #3: although the protocol seems to do unnecessary efforts when AtMostOnce DA alone is required, I must say that from the user viewpoint this DA still makes sense: the elimination of duplicates is the most important aspect of it. The inadequacy of the protocol to this DA is mostly an optimization issue (and also an unnecessary implementation burden for some cases). The other difference with AtLeastOnce DA, from the RMD-AD contract perspective, is that in the latter, an error must be raised if the message is dropped after reception.

I think the issue is a more general one: should this DA as well as other DAs be part of this spec, now that the protocol has a life of its own? I'd prefer to see DAs expressed in a different doc, or at least in a clearly separate section. Looks like another editorial issue.

Regards,

Jacques

-----Original Message-----

From: Tom Rutt2 

Sent: Wednesday, September 28, 2005 10:17 AM

To: wsrx

Subject: [ws-rx] Proposed NEW ISSUE: Alignment and Refinement of Definitions for Delivery Assurances

NEW ISSUE - Alignment and Refinement of Definitions for Delivery Assurances

Description:

I took an action Item to align the Delivery Assurance definition text in 

the body document with the resolution of Issue 009.

Source: Tom Rutt, Fujitsu

Justification:

The resolution of Issue 009 is documented at:

http://www.oasis-open.org/apps/org/workgroup/ws-rx/download.php/14682/ReliableMessagingIssues.xml#i009 

:

It is best if the Delivery assurances are defined in only one place in 

the document.

The definition of Delivery assurances is simplified by introducing the 

concept of Reliability Functions.

Proposals:

The proposal to resolve this ISSUE is presented in Three Steps.

Step 1) of Proposed Resoluton: Change the use of in line definitions in 

the proposal for Issue 009 to references to the definitions in section

Resulting text for Proposal for Issue 009:

"

<wsrm:DeliveryAssertion mode="[AtLeastOnce|AtMostOnce|ExactlyOnce]" 

ordered="[xs:boolean]"? ...="" >

/wsrm:DeliveryAssertion

A policy assertion that makes a claim as to the delivery assurance policy

observed by the destination endpoint.

/wsrm:DeliveryAssertion/@mode

This required attribute specifies which delivery assurance is asserted.

A value of 'AtMostOnce' means that the Delivery Assurance "at Most Once,

defined in section xxx, is asserted.

A value of 'AtLeastOnce' means that the Delivery Assurance "At Least Once",

defined in section xxx, is asserted..

A value of 'ExactlyOnce' means that the Delivery Assurance "Exactly Once",

defined in section xxx, is asserted.

/wsrm:DeliveryAssertion/@ordered

This attribute, of type xs:boolean, specifies whether, or not, the

"in order" reliability function defined in section xxx is asserted. .

A value of 'true' asserts that the "in order" reliability function is 

required.

A value of 'false' asserts that the "in order" reliability function is 

not required.

If omitted, the default implied value is 'false'.

"

Step 2) of Proposed Resolution: Clarify Definitions of Delivery 

assurances, using concept of reliability functions

The term "Delivery assurance" is used to refer to a set of engaged 

reliability functions associated with a Reliable Messaging Sequence.

Fundamental Reliability Functions:

* Guaranteed Receipt:

o RM-Source must buffer the message, to allow for potential 

re-transmission, until an acknowledgement is received from the 

RM-Destination for that message.

o RM-Destination must return an acknowledgment upon successful receipt 

of the message.

* Duplicate Elimination:

o No obligations on RM-Source.

o RM-Destination must not deliver to application destination any message 

which has the same ID as a previously delivered message.

In addition, to allow the definition of Delivery assurance "at most 

once", as in the resolution of Issue xx, the following "reliability 

function" is defined

* Best Effort Delivery

o No obligations on RM-Source

o RM-Destination is allowed to abort delivery of received messages to 

application destination if it cannot delivery the received message.

Note: the Best Effort Delivery function is really a function at all: it 

has no obligations, while it does have a contractual permission for not 

delivering a message which it has received. This does not seem to be a 

valid reliability function.

The following table specifies the delivery assurances in terms of 

engaged reliability functions.

Delivery Assurance |Guaranteed Receipt |Duplicate Elimination |Hold for 

Prior |Best Effort Delivery

At least once y n n n

Exactly once y y n n

'At most once' y y n y

The following reliability function may be asserted along with any of the 

above Delivery Assurances:

* In-order:

o Order is determined by the value of the RM message number. Ordered 

delivery would mean that the messages would be delivered in ascending 

order of the message number value.

o No obligations on RM-Source

o RM-Destination must hold a received message, for delivery to the 

application destination, until all messages with smaller message number 

within a sequence have been delivered to the application destination.

Note: The guaranteed delivery function is the only one which puts an 

obligation on the rm-source. All of the reliability functions defined 

above place obligations (or permissions in the case of "Best Effort 

Delivery") on the rm-destination.

------------------

Step 3) of Proposal: Refinement of DA Definitions Required to Resolve 

Discrepancy with traditional semantics of "At Most Once"

The delivery assurance "at most once", as defined in WS-rm spc, seems 

out of place. If the ws-rm spec is going to allow for "best effort 

Delivery" as a conformant behaviour contract for an RMD under special 

circumstances, why is it only allowed in combination with Guaranteed 

Delivery and Duplicate Elimination reliability functions.

I propose two ways to fix this discrepancy:

3 a) Remove the concept of "at most once" as defined in this spec.

The traditional use of the term "at most once" delivery assurance 

requires engagement of the duplicate elimination function without 

requiring the guaranteed delivery function. Since it has been agreed 

that the ws-rm protocol will always support the guaranteed Receipt 

function, this traditional concept of "at most once" is not compatible 

with this protocol.

2 b) define two new delivery assurances with Best effort Delivery (for 

consistency)

Delivery Assurance |Guaranteed Receipt |Duplicate Elimination |Hold for 

Prior |Best Effort Delivery

At least once BED y n n y

Exactly once BED y y n y

Approach 3b) adds complexity to the Delivery assurance assertion 

mechanism. It does not seem to go along with the concept of Reliable 

messaging, and systems which do this should be considered as acting 

outside the scope of the WS-rm specification.

I prefer proposal 3a).

-- 

----------------------------------------------------

Tom Rutt        email: ; 

Tel: +1 732 801 5744          Fax: +1 732 774 5133