Domainlogiikan

Domainlogiikan, or domain logic, refers to the part of software that encodes the business rules and behavior of a specific domain. It captures the concepts, constraints, and workflows intrinsic to the domain and is distinguished from user interface logic, application orchestration, and infrastructure concerns. In domain-driven design, domain logic resides in the domain layer and is expressed through a domain model that uses a ubiquitous language shared by developers and domain experts.

A domain model typically comprises entities, value objects, aggregates, domain services, and domain events. Entities have identity and evolve over time; value objects are immutable descriptors defined by their data; aggregates enforce consistency boundaries and invariants within the model; domain services implement operations that do not naturally belong to a single object; domain events announce state changes to other parts of the system. The aim is to model business concepts in a way that supports correct behavior and long-term maintainability.

The core objectives of domain logic include enforcing business invariants, encapsulating complex business rules, coordinating state changes across related objects, and maintaining model integrity under concurrency. Good domain logic is designed to be testable, with a preference for pure functions where feasible and controlled side effects confined to application services or infrastructure adapters.

Relation to other layers is essential: the domain logic sits at the core, while application logic coordinates use cases and user interactions, and infrastructure handles persistence, messaging, and external services. A common design consideration is the balance between a rich domain model and simpler, anemic models. The concept is central to domain-driven design, popularized by Eric Evans, and continues to influence enterprise software architecture.