Multitier architecture

In software engineering, multitier architecture (often referred to as n-tier architecture) is a client–server architecture in which presentation, application processing and data management functions are physically separated. The most widespread use of multitier architecture is the three-tier architecture. N-tier application architecture provides a model by which developers can create flexible and reusable applications. By segregating an application into tiers, developers acquire the option of modifying or adding a specific tier, instead of reworking the entire application. A three-tier architecture is typically composed of a presentation tier, a logic tier, and a data tier. While the concepts of layer and tier are often used interchangeably, one fairly common point of view is that there is indeed a difference. This view holds that a layer is a logical structuring mechanism for the conceptual elements that make up the software solution, while a tier is a physical structuring mechanism for the hardware elements that make up the system infrastructure. For example, a three-layer solution could easily be deployed on a single tier, such in the case of an extreme database-centric architecture called RDBMS-only architecture or in a personal workstation. The "Layers" architectural pattern has been described in various publications. In a logical multilayer architecture for an information system with an object-oriented design, the following four are the most common: Presentation layer (a.k.a. UI layer, view layer, presentation tier in multitier architecture) Application layer (a.k.a. service layer or GRASP Controller Layer ) Business layer (a.k.a. business logic layer (BLL), domain logic layer) Data access layer (a.k.a. persistence layer, logging, networking, and other services which are required to support a particular business layer) The book Domain Driven Design describes some common uses for the above four layers, although its primary focus is the domain layer. If the application architecture has no explicit distinction between the business layer and the presentation layer (i.