Process

Programs consist of many thousands of statements about how a computer should usefully work in the future. We call individuals who make these statements programmers and those who decide what would be useful, customers. S1

Extreme programming exploits the modularity that became available in the '80s to allow programmers to make and remake decisions in a closed loop with the customer. S2

Programmers deliver to their customer new functionality at a regular tempo and simultaneously deliver to their future selves opportunity to further expand the program in unforeseen ways. Various counting strategies allows reporting a working "velocity". S3