What Is Bottom Up Designing ?

Bottom-Up Design Model: 

   In this design, individual parts of the system are specified in detail. The parts are linked to form larger components, which are in turn linked until a complete system is formed. Object-oriented language such as C++ or java uses a bottom-up approach where each object is identified first. 

Advantage: 

▫️Make decisions about reusable low-level utilities then decide how there will be put together to create high-level construct.