A publish-subscribe channel aligns with the event-driven messaging model, promoting loose coupling and scalability. The event source (IoT gateway) is decoupled from the consumer (microservice), allowing the microservice to process events asynchronously at its own pace and scale independently based on the event volume, which is ideal for high-volume, variable IoT streams.

A process agent is a non-human program that automates a process step. Its primary role in service composition is to ensure the correct order of message exchanges (e.g., sending a request, waiting for a response, triggering the next step) to complete a larger, cross-service task, thereby enforcing the required sequence logic.

Fine-grained operations often require consumers to make multiple calls to perform a single business task. This intertwines the consumer’s logic with the service’s internal data model and operation structure. If the service changes its model, it may break all consumers that built complex logic around these fine-grained calls, leading to a form of tight coupling.

The event-driven pattern (publish-subscribe) excels when a single state change is relevant to multiple, unknown subscribers. If several services need the update, having Service B publish an event decouples it from all of them. New services can subscribe later without any changes to Service B, promoting scalability and flexibility.

A service composition is an aggregate of services collectively coordinated by a composition initiator (like an orchestration engine or a parent service) to automate a larger business process. A collaboration is a simpler, often peer-to-peer interaction between services without this centralized, coordinated control flow to achieve a composite task.

Postponed orchestration involves a service performing its core task and then emitting an event to announce its completion. The responsibility for determining and coordinating the next steps in the overall business process is ‘postponed’ to a dedicated coordinator (the process agent) that reacts to the event. This keeps the Inventory service simple and decoupled from the overall order process logic.

A service candidate is an abstract representation of a potential service. It is used during analysis to model capabilities, assess their alignment with business processes, evaluate reuse potential, and define functional boundaries without committing to implementation details. This helps ensure the future physical service is well-justified and designed for effective composition.

A central orchestration engine typically acts as the state manager for the long-running process. It knows which steps have completed (e.g., credit check passed) and which have failed (valuation). This centralized state management allows it to implement sophisticated failure handling, like pausing the process, retrying the valuation step later, or triggering compensation for previous steps if needed, providing clear control and recoverability.

Logic-to-Contract coupling is the preferred type. It means a consumer only depends on the service’s public contract (its interface, message schemas, and policies). The service’s underlying implementation, technology, and logic can change freely as long as the contract is honored. This minimizes the impact of change and maximizes service autonomy and evolvability.

A publish-subscribe channel aligns with the event-driven messaging model, promoting loose coupling and scalability. The event source (IoT gateway) is decoupled from the consumer (microservice), allowing the microservice to process events asynchronously at its own pace and scale independently based on the event volume, which is ideal for high-volume, variable IoT streams.0