On the Hourglass Model

The Hourglass Model The hourglass model of layered systems architecture [1] is a visual and conceptual representation of an approach to achieving a design that supports a great diversity of applications and admits a great diversity of implementations. At the center of the hourglass model is a distinguished layer in a stack of abstractions that is chosen as the sole means of accessing the resources of the system. This distinguished layer can be given implementations using components which are thought of as lying below it in the stack. The distinguished layer can be used to implement other services and applications that are thought of as lying above it. However, the components that lie above the distinguished layer cannot make direct access to the services that lie below it. The distinguished layer was called the “spanning layer” by Clark because it bridges the multiple implementation layers below it in the stack [2].