Bounded Context

A Bounded Context can be considered as a miniature application, containing its own Domain, own code and persistence mechanisms. Within a Bounded Context, there should be logical consistency; each Bounded Context should be independent of any other Bounded Context.

Bounding Contexts gives team members a clear and shared understanding of what has to be consistent and what can be developped independently. Think of an e-Commerce system. Initially you can tell it is an application of shopping context. But if you look more closely, you will see there are other contexts too, like: Inventory, Delivery, Accounts etc.

As DDD book advises:

Explicitly define the context within which a model applies. Explicitly set boundaries in terms of team organization, usage within specific parts of the application, and physical manifestations such as code bases and database schemes. Keep the model strictly consistent within these bounds, but don’t be distracted or confused by issues outside.

Smaller models provide many benefits, allowing teams to define clear boundaries relating to design and development responsibilities. They also lead to better maintainability — because a context has a smaller surface area, you have fewer side effects to worry about when making modifications.

Interaction between Bounded Contexts

Bounded contexts are autonomous components, with their own domain models and their own ubiquitous language. They should not have any dependencies on each other at run time and should be capable of running in isolation. However, they are a part of the same overall system and do need to exchange data with one another. If you are implementing the CQRS pattern in a bounded context, you need to use a special type of events for this type of communication. In Spine we use term Integration Events.

Integration Events have the same nature as events within the bounded context. They are one-way, asynchronous messages that publish information about something that has already happened.

Your bounded context can respond to events that are raised outside of the bounded context, and your bounded context can publish events that other bounded contexts may subscribe to. This enables you to maintain the loose coupling between your bounded contexts.

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