REM in Agile Projects - Requirements Engineering and Management for Software Development Projects - page 210

15.2 Extreme Programming

Extreme Programming (XP) goes through six phases, namely the exploration,
planning, iterations to release, putting into production, maintenance and
death.
In the exploration phase two main activities are carried out. The customer
writes the story cards as the first activity. Each card describes a feature and all
cards put together include all the requirements for the first release of the software.
The second activity is carried out by the developers, who familiarize themselves
with the development environment.
In the planning phase, the developers prioritize and schedule the development
for the first phase. The schedule is usually limited to 2 months.
In the iterations to release phase, multiple iterations may take place for each of
the releases. Normally no iteration would exceed 4 weeks duration. The devel-
opment team selects the stories for development in consultation with the customer.
The putting into production phase would see that one release of the software is
released to the customer after a final round of testing. If the customer asks for any
changes in the software, they will be implemented. The release process could be in
iterations, each of which would normally be limited to a 1 week duration.
After putting one release into production, the team would take up the next
release of the proposed software product.
In the maintenance phase, the development team would support the customer in
effectively

utilizing the released software. Sometimes new people could be

inducted into the team for carrying out the maintenance.
The death phase begins when the customer has no more stories that need
development of software. It also requires the stable operation of the software that
was put into production, and the development team is no longer required to support
the system in production.
As you can see, the requirements are handled in the exploration phase and the
putting into production phase. In the exploration phase, the customer writes the
user story cards. Each card would contain one feature of the software. Any
shortfalls, ambiguities or vagueness in the story cards is resolved using a face-to-
face communication with the customer who is co-located with the development
team. During the putting into production phase, the customer may request changes
in the developed software, using the face-to-face communication.
The customer is chiefly responsible for defining the requirements for the pro-
posed project. The programmers develop programs realizing the user stories.
Programmers and testers can take clarifications from the co-located customer
about the user stories whenever they require clarification.