The System Definition Model (SDM) provides the basis for the underlying metamodel used by DSD. The SDM describes distributed systems as four layers:
- Application hosts
- Network Topology
- OS and physical hardware or devices.
For each layer, the model describes the connections between systems and their configurations. By adopting a common model for all these layers, the model makes it possible for you to define and express requirements and policies across these layers. For example, an application can require a certain authentication mode or that other resources need to exist on the logical server that hosts the application. A logical server can also require that the application it hosts must support a certain authentication mode and that it disable specific features that present a security risk.
The SDM offers the following benefits:
- Provides a common language to describe the design and configuration of all aspects of a distributed system.
- Provides familiar abstractions that make it possible for developers and operations groups to communicate on common ground.
- Makes it possible for developers to communicate application requirements of the run-time environment.
- Makes it possible for operations groups to communicate application run-time, security, and connectivity requirements that result from the policies defined in the target deployment environment.
The SDM is intrinsically extensible and makes it possible for the addition of new abstract definitions at each layer.