Larger scale systems require higher-level abstractions

Over the past thirty years, abstraction techniques such as high level programming languages and abstract data types have improved our ability to specify and develop software. However, the increasing size and complexity of software systems have introduced new problems that are not solved by the current techniques. These new problems involve the system-level design of software, in which the important decisions are concerned with the kinds of modules and subsystems to use and the way these modules and subsystems are organized. This level of organization, the software archirecrure level, requires new kinds of abstractions that capture essential properties of major subsystems and the ways they interact.