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Chapter Summary

  • In this chapter, we move forward with our metaphor of EDA as the enterprise nervous system and match the EDA components—event producers, listeners, processors, and reactors—to their equivalent in the nervous system. Event producers and consumers are likened to the sensory nerve endings that pick up and relay information about our senses to our brain, which is like an event processor. Reactions, such as physical movements, are like the event reactors. For additional context and framework, we look at event-driven programming, a core technology of most PCs, as a comparable example of events, event listening, and event processing on a lower level of functioning than an EDA.
  • To complete our understanding of how EDA works, we then carry this enterprise nervous system idea further and take an in-depth look at the characteristics of EDAs and their components. Again, our focus is on the EDA of the future: an implicit, complex, and dynamic EDA, one that can adapt easily to changes and continually expand its reach of event detection and event reaction.
  • EDA components must be loosely coupled to function dynamically. Loose coupling requires that EDA components have low levels of preconception about each other and maintainability. An EDA works best if each component functions independently, with little need to know about the other components it is communicating with, and few ramifications if one component is modified.
  • EDAs, unlike conventional applications, do not rely on central controllers.
  • Events (state change notifications) are central to an EDA. An event can take the form of a message and an EDA is a message-based idea. To work, an EDA’s loosely coupled components must be able to produce and consume messages. The messages could be related to event listening, processing, or reactions. The more easily the messages can flow across the EDA (which might span multiple enterprises), the better the EDA will work.
  • Asynchronous, or publish/subscribe (pub/sub) messaging, is one of the best foundations for an EDA. As the EDA components communicate with one another, they feed messages (events) into an event bus. Event listeners receive the events, and then EDA components process the event data as required by the EDA’s designed purpose. Pub/sub is ideal for EDAs because it removes a lot of message flow dependencies from individual components. It is simpler, for example, to connect event listeners using pub/sub than to tightly couple them together, where changes in configuration are costly and slow to accomplish.
  • To achieve loose coupling and asynchronous messaging, an EDA relies on message intermediaries. In some cases, these are known as service buses.
  • The ideal EDA, therefore, is a loosely coupled, pub/sub-based architecture, with low levels of preconception and high degrees of maintainability among the components.
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