To show domain-driven design bounded contexts, map each logical context boundary directly to a distinct UML Package. Inside each package, define classes strictly belonging to that domain. You must then explicitly document dependencies between these packages using a Context Map to illustrate the relationships and data flow between your bounded contexts.

Structural Mapping Strategy

The foundation of visualizing DDD in UML lies in the direct correlation between your architectural boundaries and your diagram packages. This ensures that the diagram accurately reflects the physical structure of the codebase you intend to build.

Step 1: Define Context Boundaries

Begin by identifying the distinct functional areas of your system. These are your bounded contexts. Each context represents a specific part of the business domain with its own language and logic.

Ensure that every concept, terminology, and data structure belongs to exactly one context. If a concept is shared, it must be translated into a different form for the receiving context. This step prevents ambiguity in your model.

1. List all major business processes.
2. Group related processes into logical boundaries.
3. Assign a unique name to each boundary, such as “Order Management” or “Customer Service”.

Step 2: Create Corresponding Packages

Once boundaries are defined, create a UML package for each context. Use the context name as the package name. This direct mapping makes the diagram readable for developers and architects alike.

Each package will serve as a container for the specific classes, components, and diagrams that belong to that domain. It acts as a namespace that enforces separation of concerns.

Step 3: Populate Package Contents

Move the domain entities, value objects, and aggregates from your analysis phase into the correct package. Do not mix classes from different contexts within the same package. This strict adherence maintains the integrity of the bounded contexts UML packages approach.

Ensure that each package contains only the specific interfaces required for that domain. If a class needs to interact with another context, define the interaction through the package boundary, not by direct class access.

Step 4: Document Dependencies

Use dependency arrows to show relationships between the packages. This creates the visual structure of the Context Map. Distinguish between different types of relationships, such as “Partnership,” “Customer-Supplier,” or “Open Host Service”.

Keep the number of dependencies low. A highly coupled package structure indicates a failure in the modularization strategy. Aim for high cohesion within packages and low coupling between them.

Managing Context Relationships

Visualizing the boundaries is only half the work. You must also clearly represent how these boundaries interact. A bounded context does not exist in isolation; it exchanges data and services with others.

Identifying Relationship Types

Not all dependencies are created equal. You need to classify the interaction between your contexts to understand the risk and complexity involved in the system.

• Corollary Relationships: One context depends on another, often for reference data. The direction is unidirectional.
• Upstream/Downstream: One context (upstream) provides an API that another (downstream) consumes. Changes upstream may break downstream logic.
• Shared Kernel: Two contexts share a common set of models or code. This is risky and should be minimized.

Visualizing the Context Map

Create a dedicated diagram that shows only the packages and the arrows between them. This high-level view helps stakeholders understand the flow of information without getting lost in class details.

Label the arrows with the relationship type. For example, label an arrow “Open Host Service” if one context exposes a well-defined API for others to use.

Advanced Implementation Patterns

In complex systems, simple package boundaries might not be enough. You may need to introduce additional structures to represent specific integration patterns or anti-corruption layers.

Implementing Anti-Corruption Layers

When an external system has a different model, you cannot simply import its classes into your package. Instead, create an “Anti-Corruption Layer” package.

This package acts as a translator. It contains the adapters and mappers that convert the foreign data model into your internal domain model. This prevents the external logic from polluting your bounded context.

Handling Shared Kernels

Sometimes, sharing code between contexts is necessary for efficiency. If you must share a common kernel, keep it in a separate, isolated package.

Mark this package as shared in your documentation. Clearly document the contract that both contexts must agree upon. Any changes to this shared package require careful coordination.

Managing Package Dependencies

Use UML package dependencies to enforce strict dependency rules. Ensure that “downstream” contexts do not depend on “upstream” contexts unless explicitly designed to do so.

This prevents the “spaghetti architecture” where all packages depend on everything. The structure should support independent deployment and testing of bounded contexts.

Solving Common Model Conflicts

Modeling large systems often leads to conflicts. These arise when domains overlap or when teams interpret the same concept differently. Structured packages help resolve these issues.

Resolving Name Collisions

Different contexts might use the same name for different concepts. For instance, one context might call an entity a “Customer” while another calls it a “Client”.

Keep these in separate packages to avoid confusion. Do not try to force them into a single global namespace. The package boundary acts as the qualifier for the name.

Preventing Domain Bleeding

Domain bleeding occurs when a class in one context directly references the internal details of another context. This breaks encapsulation and creates tight coupling.

Fix this by refactoring the code to use interfaces or data transfer objects (DTOs). Ensure that your UML packages only show these interface-based connections, hiding internal implementation details.

Validation and Verification

Once you have built your model, you must verify that it adheres to DDD principles. The structure of your bounded contexts UML packages should be evident and robust.

Checking Package Cohesion

Review each package to ensure that the classes within it are highly related. If a class feels out of place, move it to its correct context or create a new package.

A package should represent a single responsibility. If it tries to do too much, it is likely a sign that the context boundary is too wide.

Reviewing Dependency Cycles

Ensure there are no circular dependencies between your packages. A cycle between two bounded contexts indicates a lack of clear boundaries or a shared responsibility issue.

Break the cycle by introducing an intermediary interface or by refactoring the logic so that one context does not depend on the other.

Key Takeaways

• Map each DDD bounded context directly to a distinct UML package for clear structure.
• Use dependency arrows to visualize context maps and relationship types like Customer-Supplier.
• Keep packages isolated to prevent domain bleeding and maintain low coupling.
• Implement anti-corruption layers in packages when integrating with external systems.
• Verify that no circular dependencies exist between your bounded context packages.