Discuss the reuse of software at a different levels

The reuse of software can consider at a number of different levels:

1. Application system reuse: The whole of an application system may be reused. The key problem here is ensuring that the software is portable; it should execute on several different platforms.
2. Sub-system reuse: Major sub-system of an application may be reused. For example, a pattern-matching system developed as part of a text processing system may be reused in a database management system.
3. Module or Object reuse: Components of a system representing a collection of function may be reused. For example, an Ada package or a C++ object implementing a binary tree may be reused in different applications.
4. Function reuse: Software components, which implement a single function, such as a mathematical function, may be reused.