DE also supports application engineering which uses the models and architectures to build systems. The emphasis is on reuse and product lines. Domain models represent the set of requirements that are common to systems within a product line . There may be many domains, or areas of expertise, represented in a single product line and a single domain may span multiple product lines. A product line definition will describe the domains necessary to build systems in the product line.
Software architectures are the structures used to build systems in a product line.
The developer then uses the product line architecture to build the system. The SEI has developed a framework for product line practice . This framework describes product line practice essentials, accommodates the various starting points at which an organization might find itself, and outlines recommended steps and practices that an organization should adopt to move closer to sound, repeatable product line development.