The purpose of a piece of software is the starting point for the analysis phase. The purpose and functional requirements can be defined in terms of inputs, processes and outputs.
Analysis is the first phase of software development. A client will ask a software development team to develop a piece of software. To begin with, a systems analyst will meet with the client to determine:
the purpose of the software
the functional requirements of the software
The purpose of a piece of software is often expressed as a description of what the software will be used for. The functional requirements will specify inputs, processes and outputs.