Subsystem is generally said that there is a certain function of the system, and the usual "module" concept similar
For example, for a monitoring system, we can say that "data acquisition subsystem", then the subsystem is to complete the data collection task of a relatively complete combination of functions.
In order to avoid the large number of things intersecting each other, we need to consider a large number of relative relationships. Sub-Systems We usually divide a complex system into several independent subsystems so that we can consider these subsystems independently And then independently consider the relationship between the various things in each subsystem.
Subsystems and components
The component belongs to the implementation category; Sub-Systems in order to represent the component in the design, the subsystem can be used as a proxy for the component.
Each part of the system should be as independent as possible from the rest of the system. In theory, it should be possible to replace any part of the system with new parts, provided that the new part must support the same interface. Should be able to make the different parts of the system independently evolved, Sub-Systems without being affected by other parts of the system. To this end, the design subsystem provides an ideal way to represent components in a design model: they are design elements that are used to encapsulate many classes of behavior (as if a component encapsulates many instances of an instance) and can only pass them The implementation of the interface to access their behavior (component is the case).
A subsystem that represents an existing product
If the existing product is a product that is used to export the interface (that is, it is possible to export), but it hides all the details of the implementation, Sub-Systems the product can be modeled as a subsystem in a logical view. You can use the subsystem to represent the products used by the system, for example:
Communication software (middleware). Database Access Support (RDBMS Mapping Support). Application-specific products. Some existing products, such as type collections and data structures (for example, stacks, lists, queues) are best represented by packages, because they show more than just behavior. Both important and useful is the specific content of the package, not the package itself, but it is a container.
For commonly used utilities (such as math libraries), Sub-Systems if they only export the interface, they can be expressed as a subsystem, but whether it is necessary or meaningful, but also depends on the designer to determine the nature of the modeling object. Subsystems are object-oriented constructs that are not only classifiers, but also packages: subsystems can have instances (if the designer makes such a designation). With UML, you can also create models of multiple sets of global variables and procedures in the utility as a constructor class (no examples of the utility).
When defining a subsystem to represent a product, define one or more interfaces to represent the product interface.