Saturday, July 02, 2011

Business Event Subscriber Responsibility?

Thought I would write a comment about what are some of the expectations of a business event subscriber.  These would be rules that the business event publisher could depend on.  These sets of rules form the basis for Event Driven Architecture (EDA) based implementations.

Subscribers of business events and business alert notifications often assume that the business event publisher is responsible for insuring that duplicate events and any repeat alert notifications are suppressed. However, to protect itself the subscriber has to be able to "analyze" the business event to determine if the erroneous event/ alert was sent by the business event provider, messaging architecture or the enterprise service gateway. The subscriber (business application, business process) would have to "know" when to discard the business event as being a duplicate event, as well as when to re-apply the same business event, which could have been issued as a result of change in the business policy or due to an increase in the business alert thresholds.  Knowing when an event transmission is real versus a false notification insures that the outcome of the EDA implementations are valid.

For instance, if a "low inventory alert" is received by the Purchasing Process it may react to this alert notification by transmitting a PO to the supplier. However, if the same Purchasing Process gets a second alert a few seconds or a few minutes later chances are the Purchasing Process may choose to ignore this. Not examining the alert more closely may cause it to erroneously discard the alert.  It is possible that in order to optimize and tune the response processing the subscription process just looks at the product and quantity to de-dup alerts received within a certain period thus causing the second alert to be discarded. The business impact of ignoring the second alert was failure to increase in the "minimum product level". The bottom line, the subscribing process has to know how to differentiate between fundamental business rule changes and duplicate alerts and not have a compute process optimization overrule business policies.

In general, in an event driven architecture realm the disconnectedness of the publisher/ subscriber pair places a burden on both parties to insure that there exists a mechanism and rules to enable "semantic" translation of the message payload that carries the business event or the business alert.  Without investing in the definition and analysis of these semantics benefits of the loose coupling EDA architecture would deliver a scalable technical architecture model but would not yield the right business outcome.

It must be noted that standards such as WS Eventing, WS Base Notificaitons and WS Notification help to define WSDL and XML Schemas for defining the mechanics of loosely coupled and inter-operable EDA implementations but the business semantics and rules in constructing and consuming the events are not really well laid out.  Not having had exposure to specifications such as ebXml and OAGIS business documents I assume some of the B2B interactions may have more mature semantic definition but for the most part I think these rules of engagement may still need to be fleshed out by the participating parties.

Thoughts and feedback on this topic would be very useful.
surekha -

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