Subsystems are generally said to have a certain function of the system, and the commonly said "module" concept is similar
For example, for a monitoring system, we can say that there is a "data acquisition subsystem", then this subsystem is to complete the data acquisition task of a relatively complete function of the combination.
In the process of analyzing the problem, in order to avoid a large number of things intersect, so we need to consider a large number of relative relationships, Sub-Systems we usually divided a complex system into several separate subsystems, so that we can independently consider the relationship between these subsystems, Sub-Systems and then independent of each subsystem within the relationship between the things.
A subsystem is a model element that has the semantics of a package (which can contain other model elements) and a class (its behavior). The behavior of a subsystem is provided by the classes or other subsystems it contains. Subsystems implement one or more interfaces that define the behavior that a subsystem can perform. Subsystems can be used in a variety of complementary methods to use the subsystem, the system is divided into several units, these units: can be independently scheduled, configuration or delivery can be developed independently (as long as the interface remains unchanged) can be deployed independently on a set of distributed compute nodes without destroying the rest of the system to make changes in addition, subsystems can be divided into several units to provide limited security for critical resources in a design that represents an existing product or external system