RE: [ebxml-msg] MOU on intermediate support by conformance profile and o

Here are some reasons why I would prefer to use ebMS headers for routing rather than WS-Addressing Reference Parameters:

Conformance to v3.0 Core

The ebMS 3.0 Part 1 Core does not specify the use of WS-Addressing.

<JD> Right, although we know the use of RM (WS-RX) automatically requires some level of support to wsa. RM Acks need be routed based on the content of wsrm:CS/ AcksTo, which is an EPR. It will be expected this EPR has enough value to either directly send the Acks, or to route them. The associated ref parameters are supposed to be put in the header and are a natural fit for routing... All this was not so crucial for point-to-point exchanges where an "anonymous" value is expected most of the times in the AcksTo

Our engineering believes it is easier to do an "wsa extension" to a Core MSH vs. to add generating a (dummy) eb:header in some cases and is a bit cleaner from architecture viewpoint.

Avoid yet another standard to support

Requiring support for WS-Addressing in a multihop context adds a burden to implement ebMS 3.0 in general and the multihop profile in particular.It is also true that the counterproposal requires adding ebMS headers in some situations where v3.0 Core does not require them, but any ebMS 3.0 implementation needs to know how to construct or handle ebMS 3.0 headers anyway, so this is just a reuse of that general functionality.

<JD> WS-addressing support is greatly facilitated by current WS stacks which provide APIs to add / consume wsa headers.

We need to look at the corner cases as well, where I think wsa may have an edge:

- if an ebMS intermediary has to generate an eb:Error, the routing of this error cannot always rely on a "reverse reading" of the eb:Header of the faulty message for back routing. Wsa provides wsa:From and wsa:ReplyTo headers that contain the same value type (EPR) as the wsrm:AcksTo, and that could be used for this.

- we still have the problem of routing eb:Signals (Receipts, Errors) that originate from the ultimate receiver. Although we can generally assume the eb:header of the related User message can be used for reverse-routing of these, I feel more comfortable with an alternate capability that allows for different routing data including a direct URL when possible (in same way as wsrm:AcksTo does for RM Acks). wsa:ReplyTo and wsa:From support this.

- what if some User messages have new header data that are intended to the same MSH as others, but for which I-Cloud routing functions have not yet been updated (e.g. a business partner behind a MSH decides that its sub-departments will now have their own PartyId). I like the idea that one can still reuse an old EPR data that is known to route properly, assuming that when both wsa ref param headers AND eb:header are present, routers look first at wsa ref param headers.

- bundling: as discussed in F2F, it could be that several UserMessage elements have to be bundled. Relying on eb:headers for routing in such cases, imposes several restrictions on how bundling can be done. Giving precedence to wsa ref param headers for routing is an unambiguous solution (see previous case of not up-to-date routing functions).

Inconsistency

If we start using WS-Addressing reference parameters in the multihop context, the question comes up why we did not use them in ebMS 3.0 Core. There are already elements in the ebMS header that are also in WS-Addressing, such as MessageId. Nevertheless, v3.0 Core does not use WS-Addressing even for these header fields, let alone use reference parameters for the information types that are in an ebMS 3.0 header but are not regular WS-Addressing field. I think the ebMS 3.0 header is richer than WS-Addressing header, so that this decision was right at the time. But even if it were not, I think a multihop profile should stick to the approach taken in v3.0 Core.

<JD> we discussed a lot about wsa:MessageId in the past. One of the reasons to not rely on it was in case of bundling: the identity has to be per message unit (eb:UserMessage or eb:SignalMessage). We already have in Core V3 some limited cases of bundling Signal + User units. eb:Errors may need to selectively refer to these based on eb:messageId.

Limited reuse

It might look as if using WS-Addressing is an instance of reusing a more general specification instead of defining ebMS specific mechanisms. But unlike the reuse of WS-Security or WS-Reliability/WS-ReliableMessaging, this reuse is only a syntactic issue. We would just be adding information to some defined extension points in the schema. Any processing of that information would require ebMS-specific processing, rather than using generic WS-Addressing functionality. Any intermediary that provides WS-Addressing functionality and wants to conform to this profile would still need to have ebMS-specific functionality.

<JD> But we could say as well that it is in the nature of wsa to be a "syntactic specification", i.e. unlike WS-RM or WSS it does not define precise mechanisms: only some mappings between EPR construct and header content, as well as some limited control of the HTTP binding and some cross-message correlation features. Now, besides the header aspect, the notion of EPR appears to be a convenient modeling construct that can be reused in PModes, and is able to wrap up all data needed for routing, with ref parameters.

Duplication in message structure

Having to store or retrieve the same type of information in two different locations usually smells of missed generalizations, and I think that is true here too. We looked at putting the equivalent of an ebMS header in a URL (the earlier HTTP URL query parameters), I don’t find putting it in WS-Addressing parameters a lot more elegant. It also raises issue like how to handle any inconsistencies in situations where there is both a WS-Addressing structure and an ebMS header. Also, the WS-Addressing specification says that using reference parameters to store information that would otherwise be in other SOAP headers could cause “unintended or erroneous semantics in the resultant SOAP message".

<JD> this is a possibility. But if we make it clear what the routing precedence rules are, we have to consider the good side of discrepancies: in some cases - e.g. delay in updating the routing functions: you don't want to or can't rely on the eb:header. So discrepancy may be intentional. Given taht the eb:header is primarily intended for message binding after reception, while wsa ref params are only for routing, having an exact map should not be always expected or required.

Generalized routing

This is related to duplication. When using just ebMS headers, assuming routing is done on destination PartyId, any message (user, signal, WS-* helper, bundles, piggy backs) can be routed based on the single following XPath expression:

S:Envelope/S:Header/eb3:Messaging/eb3:UserMessage[1]/eb3:PartyInfo/eb3:To/eb3:PartyId

<JD> assuming the use of dummy eb:headers, yes. But again, there are seveal other factors to consider.

Yes, I agee that adding metadata to ebMS signals or to other messages used in WS protocols is what is agreed upon as a MOU item.

The way or ways to do this is apparently TBD J

I think that since we have several ways to attach the metadata, we probably want to prune these down into a simple convention to do it in a standard way.

(Incidentally, would we then provide CPPA support for these messages? Would they be treated as msh level messages from the default packaging and delivery channel standpoint?)

From: Pim van der Eijk [mailto:pvde@sonnenglanz.net]
Sent: Wednesday, May 07, 2008 1:04 PM
To: Moberg Dale; ebxml-msg@lists.oasis-open.org
Subject: RE: [ebxml-msg] MOU on intermediate support by conformance profile and other auxiliary documents for ebMS 3.0

We agreed to add ebMS metadata also to signals and helper messages. And we also looked in some detail at one option for adding this metadata, by adding it to a WSA header. Imo we did not fully compare this option to using a an eb:Messaging header (containing an eb:UserMessage but one that has no eb:PayloadInfo) to convey the ebMS metadata. I want to fully understand both options and compare their pros and cons. Unfortunately, due to travel I will not be able to attend next week's meeting.

Pim

From: Moberg Dale [mailto:dmoberg@axway.com]
Sent: 07 May 2008 19:42
To: ebxml-msg@lists.oasis-open.org
Subject: [ebxml-msg] MOU on intermediate support by conformance profile and other auxiliary documents for ebMS 3.0

Goals

Transparency where feasible

Signature intact where feasible (important aspect of transparency)

WSI Conformance where feasible (especially with respect to WSI RSP policy that WS-RX Reliable Messaging headers be signed, including WS-Addressing elements where used within ReliableMessaging)

Spoke configuration to services within an I-Cloud should have simplicity of configuration change management.

Specifically, rerouting to services (within the I-Cloud ) can be accomplished without spoke configuration changes”)

Hub service destinations and spoke clients have “vanilla” ebMS 3 conformance where feasible. (Some specializations of general functionality and of extension points is allowed.)

Additional Implicit Constraints

The internal addresses within an I-Cloud can have private IP addresses and DNS names that are not publicly reachable or resolvable in the Internet.

Proposed

Rerouting by intermediaries can be based on ebMS “metadata” both in forward and return paths.

This functionality is referred to as a “table” mapping ebMS metadata to next hop URLs so that the HTTP POST (or other?) command can be rewritten.

TBD: This map may be augmented for return paths by keeping a map involving Message-Id and Relates-To values.

For ebMS user messages, no special treatment is needed (so far anyway).

For ebMS signal messages and for WS clerical messages (such as CreateSequence, CreateSequenceResponse, etc.) several approaches are under consideration

1. Define a ebMS Reference Parameter that allows the wsa attribute “isReferenceParameter” applied and that contains the metadata needed for routing.

2. Allow use of WS-Addressing headers such as From or ReplyTo or FaultTo that have an EndpointReference model (and include ReferenceParameter within the EPR).

3. For return path, if WS-Addressing Messaging-Id was present in incoming message, require use of RelatesTo in response message.

4. For using the request connection for a response, some read-only access to ReplyTo is needed to check for the “anonymous” URL value.

In this case, all intermediaries would be expected to hold the connection open (?) to allow the final service to use the HTTP backchannel for its response.

For Pull MEP-binding, allow first intermediary to handle MPC requests and let internal I-Cloud arrangements for this option be implementation specific.

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