Key Learnings - Using EDA to implement the core SOA principle of "loose-coupling"!!!

A lot has been said about how SOA and EDA are unique "architecture styles". It seems like only one or the other architectural principle is considered in proposing architectural solutions. However, there is a distinct benefit to using both paradigms in unison in solving business problems!!


Business events are the "core concept" that drive any EDA implementation. On the other hand, decoupling business applications and the business functions/ business processes embedded in these business applications is the core theme of SOA. SOA implementations rely on the use of standards based web services technology stack and that of canonical business documents (XML) .

However, it is my contention that an enterprise that does not invest in the web services or ESB technology can still leverage EDA style business events to implement loosely coupled business services provided it makes an effort to analyze its' business events and creates canonical representations of these key business events. This could mean defining business events that encapsulate a business concept that have an associated business concept state indicator or a business action indicator. Further, these business events can be used to trigger constructs such as event handlers that act as a facade or layer of indirection to execute a business function via the use of an application API.

It must be noted that the terms event producers and event consumers or publishers/ subscribers are being used loosely to denote the initiator of the event and the owner of the business behavior that "knows" how to deal with the event. In a SOA realm this would be the service consumer and the service provider respectively.

The key to this model in leveraging SOA is the use of self-describing canonical business events that are subscribed to by independent event listeners. These event listeners and/or event handlers that are delegated to by these event listeners help insulate the event producers and event consumers from the complexity of knowing how to interpret the events. Here the event producers/ publishers and event consumers/ subscribers are decoupled from one another via the use of canonical business events as well as messaging technologies.

Either of the two layers i.e. the event publisher or event subscribers can be altered long as the contract is adhered to in terms of the canonical business events. Also, messaging technology oriented configuration consoles allow the definition of the event publisher/ subscribers to be connected via metadata as opposed to hard-wiring these in code. Event handlers act as event adapters in that these could translate the event and invoke the required API call to deal with the event. The event handlers act as a business facade that hide the workings of the business application and allows the business application to change without affecting the event producers.

To recap, if loose-coupling is a core SOA principle that promotes business agility then the use of event handlers invoked using messaging technology and canonical business events can be used to deliver this goal. The enterprise does not need to invest in a SOAP stack right away to achieve this goal. If desired technology standardization and interoperability can be introduced at a later phase by turning these event handlers into web services. This two phased approach defined above enables the enterprise in pushing off investment in the technology stack to a future phase without sacrificing business agility and/or offering novel business capabilities.

 
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surekha -