Ntier

Ntier (often written N-tier) is a software architectural pattern that divides an application into multiple layers, or tiers, each encapsulating a distinct concern. Tiers communicate with adjacent tiers through well-defined interfaces, and the overall system behavior emerges from their collaboration. The designation N-tier emphasizes that the number of tiers can vary; common implementations include two-tier, three-tier, and other multi-tier configurations.

Typical tiers include: presentation tier (user interface), business logic tier (application processing, validation, workflow), and data tier (database or data services). In many web applications the presentation tier runs on the client, while the business logic and data access layers reside on one or more server-side tiers. Some architectures add additional tiers such as an integration or service tier, caching layer, or security/authentication layer.

Benefits of Ntier architecture include improved scalability, since tiers can be scaled independently; increased maintainability and reuse of components; clearer separation of concerns; and more flexible security boundaries. It also supports distributed development and easier testing of individual tiers.

Drawbacks include added complexity and deployment overhead, potential latency from cross-tier communication, and challenges in managing transactions and data consistency across tiers. Over time, teams may evolve toward service-oriented or microservice styles that preserve tiered boundaries while enabling finer-grained deployment.