Applying Domain-Driven Design: A Restaurant Case Study for Architecture and Domain Modeling

1. Domain Design

The core of domain design is business‑driven decomposition, aiming to narrow the gap between the software system and real business, thereby reducing complexity and confusion.

First, thoroughly analyze the business and then design a software model that corresponds to the business model, which is the essence of DDD.

1.1 Macro Process

Using a restaurant as a virtual scenario, the macro process identifies major functional areas such as the "Dish Domain", "Order Domain", "Kitchen Domain", and "Dining Domain".

1.2 Unified Language

A consistent language throughout the development lifecycle clarifies roles, behaviors, and entities, forming the basis for clear domain concepts.

1.3 Use‑Case Analysis

Focus on the relationships between roles and behaviors to guide domain partitioning and service design.

1.4 Domain Partitioning

Domains are divided based on functional relevance (the primary criterion) and, when necessary, role relevance, ensuring each domain remains autonomous.

1.5 Domain Services

Domain services implement use‑cases and should be defined per role, mapping each role to a corresponding service (e.g., chef service, procurement service).

1.6 Domain Modeling

Modeling centers on business concepts rather than data structures, avoiding over‑emphasis on entities and ensuring the model reflects real business actions.

1.7 Aggregation and Composition

Aggregation denotes a weak relationship, while composition denotes a strong, lifecycle‑shared relationship; both are illustrated with restaurant examples.

1.8 Upstream/Downstream Relationships

These relationships describe data flow and logical influence between domains, guiding the order of data availability and reducing unnecessary dependencies.

2. Architecture Design

Architecture addresses system complexity by defining clear layers: Interface Layer, Domain Use‑Case Layer, Domain Model Layer, Dependency Layer, and Infrastructure Layer.

2.1 Layered Architecture

Each layer has distinct responsibilities, with the interface layer exposing services, the domain use‑case layer handling business logic, the domain model layer containing entities and value objects, the dependency layer managing external integrations, and the infrastructure layer providing technical utilities.

2.2 Architecture Mapping

Domain partitions are mapped to architectural elements at matching levels (system → application → module → sub‑module), ensuring consistent naming and alignment.

2.3 Constraints

Key constraints include keeping lower layers stable, adhering to object‑oriented principles for rich models, separating business‑related layers from technical layers, and maintaining domain autonomy.

2.4 Microservice Division

Microservices are defined by domain boundaries; for the restaurant example, separate services for Kitchen, Dish, and Order are recommended, with a façade service for external access and a base service for shared utilities.

3. Functional Design (Use‑Case Implementation)

Functional design translates the architectural and domain decisions into concrete implementations, ensuring that each function follows the "open for extension, closed for modification" principle.

3.1 Concept of Function

Functions evolve over time; therefore, they must be abstracted to higher‑level concepts (e.g., from "make fried rice" to "cook dish").

3.2 Position of Use‑Cases

Use‑cases are placed within the appropriate domain based on functional relevance and role relevance.

3.3 Event Storming

Event storming helps decompose complex business processes into steps, roles, events, and entity dependencies.

3.4 Use‑Case Analysis

Identify commonalities and differences to enable reuse and extensibility.

3.5 Use‑Case Implementation Classes

Design domain service class structures that map roles to service classes and methods.

3.6 Use‑Case Flow Diagram

Assign each step to a method in the appropriate service class, linking steps with domain events.

3.7 Activity/Sequence Diagrams

Sequence diagrams illustrate internal interactions within domain services and their dependencies on domain entities.

Overall, the article demonstrates how DDD can be systematically applied to turn a real‑world scenario into a well‑structured software system where business and technical concerns are cleanly separated and mapped.