AR-8: Extract Shared Kernel

Extracts a new Bounded Context from a Shared Kernel relationship. It further established two upstream-downstream relationships so that the existing Bounded Context can use the ‘shared’ functionality.

Context & Rationales

The Shared Kernel pattern describes a close relationship between two Bounded Contexts which share a certain part of their domain models. The pattern is typically implemented as a shared library which is maintained by both teams. However, both teams depend on that shared code and each team has to deal with changes of the other one. If such a shared library gets very big and difficult to maintain it may be better to create a separate Bounded Context for it. A dedicated team may maintain the model within this new Bounded Context.

Goal

This Architectural Refactoring (AR) extracts a Shared Kernel into a new Bounded Context. The resulting Context Map will no longer contain the Shared Kernel relationship, but two new upstream-downstream relationships between the new and the existing two Bounded Contexts. This AR can be applied if a Shared Kernel gets big, difficult to maintain, and it may be better to have a new team maintaining this shared part of the domain model in a separate Bounded Context. This may increase the autonomy of all involved teams.

Extract Shared Kernel Illustration

Preconditions

  • Your model needs at least two bounded contexts which are in a Shared Kernel relationship.

Input

  • The Shared Kernel relationship.

Output

  • A new Bounded Context for the shared domain model parts and two new upstream-downstream relationships between the new and the existing two Bounded Contexts.

Example

The following example illustrates how this AR can be applied. The corresponding sources can be found in our examples repository.

Input

The following model contains a Shared Kernel relationship. Therefore the AR is available with a right-click on the relationship (arrow):

Extract Shared Kernel Example Input

Result

The resulting model contains an additional Bounded Context for the Shared Kernel (shared model parts) and two new upstream-downstream relationships between the new and the existing Bounded Contexts:

Extract Shared Kernel Example Output

Example Sources

  • You can find the CML sources for this AR example here.