Conceptual, Logical, and Physical Views
For all architectural perspectives there are various views of the architecture that are often classified as conceptual, logical, and physical views. Conceptual views are the most abstract and tend to be described in terms that are most familiar to the (non-IT professional) users of the system. The conceptual view is used to define the functional requirements and the business users' view of the application to generate a business model. Logical views show the main functional components and their relationships within a system independently of the technical details of how the functionality is implemented. Architects create application models, which are logical views of the business model, as they determine how to meet business objectives and requirements. The application models represent the logical view of the architecture for an application. Physical views are the least abstract and illustrate the specific implementation components and their relationships. Each of the elements in the physical view is implemented, normally by a design and development process, as a software or hardware system. This implementation view is normally owned by the development or operations organizations within an organization and so is outside the scope of this document.

Enterprise Architecture
Defining the overall form and function of systems (business and IT) across an enterprise (including partners and organizations forming the extended enterprise), and providing a framework, standards and guidelines for project-level architectures. The vision provided by the Enterprise Architecture allows the development of consistent and appropriate systems across the enterprise with the ability to work together, collaborate, or integrate where and when required.

Project-Level Architecture.
Defines the form and function of the systems (business and IT) in a project or programme, within the context of the enterprise as a whole and not just the individual systems in isolation. This project-level architecture will refine, conform to and work within the defined Enterprise Architecture.

Application Architecture.
Defines the form and function of the applications that will be developed to deliver the required functionality of the system. Some of this architecture may be defined in the Enterprise and Project-level Architecture (as standards and guidelines) to ensure best-practice and conformance to the overall architecture.