Difference between the Domain Services and Application Services

Domain Services vs. Application Services

Characteristic	Domain Services	Application Services
Purpose	Handles complex business rules not easily categorized within a specific part of the business. Implements the core domain logic, including business rules, calculations, and validations. Not focused on typical CRUD operations.	Coordinates the execution of domain services to fulfill application use cases. Provides an API for external consumers to interact with the application's domain logic. May handle tasks like authentication, authorization, and auditing.
Scope	Implements core, use case-independent domain logic. Manages intricate business rules that do not naturally fit within a domain object.	Implements use case-specific logic. Manages the order of domain service executions to achieve specific application functionalities.
Inputs and Outputs	Typically deals with domain objects (entities, value objects). Returns results in the form of domain-specific entities or value objects.	Typically involves Data Transfer Objects (DTOs) for input and output. Returns results in a format suitable for external interactions.
Consumers	Typically consumed by other Domain Services or Application Services. Can be utilized by different parts of the system to access specific domain functionalities.	Typically consumed by the Presentation Layer or Client Applications. Serves as an interface for external systems to interact with the application's features.
Dependencies	Independent of external concerns, such as infrastructure or presentation. Focuses solely on encapsulating and executing domain logic.	Aware of infrastructure and presentation concerns but abstracts them away from the domain model. Bridges the gap between the domain logic and external components.
Responsibilities	Manages complex business rules that cross multiple use cases. Ensures the integrity and consistency of the core domain logic.	Coordinates the sequence of domain service executions to accomplish specific tasks. Handles cross-cutting concerns like security and auditing.

Examples for each difference for better understaing:

1. Purpose:

• Domain Service:

  1. Managing and calculating risk factors in an insurance underwriting system.
  2. Validating and processing complex medical billing codes in a healthcare application.
  3. Handling intricate inventory allocation logic in a supply chain management system.
  4. Executing sophisticated fraud detection algorithms in a financial transaction system.

• Application Service:

  1. Coordinating the user registration and authentication process in a web application.
  2. Coordinating the workflow for processing customer orders and managing order fulfillment.
  3. Providing an API for external systems to interact with a recommendation engine in an e-commerce platform.
  4. Handling user session management and access control in a content management system.

2. Scope:

• Domain Service:

  1. Implementing generic business rules for handling internationalization and localization.
  2. Managing and enforcing compliance with industry-specific regulations across the application.
  3. Handling complex currency exchange rate calculations in a financial application.
  4. Implementing rules for determining eligibility and benefits in an insurance claims system.

• Application Service:

  1. Managing the workflow for user profile creation and account settings in a social networking platform.
  2. Coordinating the process of generating and sending invoices to customers in a billing system.
  3. Handling the registration and authentication process for users in a mobile banking application.
  4. Coordinating the approval process for user-generated content in an online community platform.

3. Inputs and Outputs:

• Domain Service:

  1. Receiving and processing complex financial transactions and returning updated account balances.
  2. Handling input data related to scientific experiments and returning analyzed results in a research application.
  3. Processing and validating legal documents to update the state of legal entities in a legal management system.
  4. Receiving complex configuration data for manufacturing processes and returning optimized production plans.

• Application Service:

  1. Receiving user registration data and returning authentication tokens for access to the application.
  2. Handling input data from an online shopping cart and returning order confirmation details.
  3. Receiving and validating user input for a search query and returning relevant search results.
  4. Processing user input for flight booking details and returning a confirmed booking status.

4. Consumers:

• Domain Service:

  1. Consumed by other Domain Services for advanced statistical analysis in a data analytics platform.
  2. Used by backend processes for handling complex order processing logic in an e-commerce system.
  3. Accessed by reporting services to generate detailed financial reports based on historical data.
  4. Utilized by decision-making modules for processing complex scenarios in a simulation environment.

• Application Service:

  1. Consumed by the presentation layer for orchestrating user interactions in a web-based CRM application.
  2. Accessed by mobile applications to coordinate the submission and tracking of service requests.
  3. Utilized by external partners via API to integrate with a recommendation engine in an online streaming service.
  4. Consumed by external systems to access user authentication and authorization services in a cloud-based platform.

5. Dependencies:

• Domain Service:

  1. Independent of infrastructure concerns, focusing solely on encapsulating business logic for complex mathematical calculations.
  2. Not reliant on presentation layer details, ensuring the integrity of core domain logic for regulatory compliance checks.
  3. Free from dependencies on external APIs, maintaining autonomy in processing industry-specific rules.
  4. Not coupled with specific database technologies, allowing flexibility in handling diverse data sources.

• Application Service:

  1. Aware of infrastructure details to abstract them from the core domain logic, facilitating scalability in user authentication.
  2. Dependent on external services for sending notifications and managing communication with users.
  3. Informed about presentation layer requirements, abstracting them to provide a consistent interface for external consumers.
  4. Tied to specific data storage solutions for managing user sessions and access control in a scalable manner.