Sviluppo dei sistemi di informazione: Appunti di Sistemi

Chapter 10. Developing information systems

Every software development project faces a tension among time, cost, and quality, and they imply a trade-off among the three elements. Usually, it is true the saying: "You want it fast, good, and cheap? Pick any two.” Developing a software is a complex, time-consuming, and costly endeavor, and so it is crucial to use a framework.

Development methodology

A software development methodology is used to plan, structure, and control the software development project. The framework can be unique for the entire organization or it can be different depending on the projects.

System development life cycle (SDLC)

The traditional approach is the system development life cycle (SDLC) that provides a disciplined approach to system development. This kind of approach is a waterfall method since the result of one phase flows as inputs into the next phase. Sometimes you need to go back and refine an earlier phase based on new information that emerges. The steps are:

Planning phase

• Define the overall goal and scope of the new system and determine the feasibility of the project. There are different aspects of feasibility: technical, economic (system affordable and worthwhile), organizational, legal, and ethical.

Requirements phase

• Uncover and document the functions that the system should provide and desired levels of performance (figure out and document what the system should do). There are two kinds of requirements: functional (how the system should interact with users and other systems) and non-functional (the constraints of the system).
• The main task of this phase is the requirements elicitation, which is to gather requirements from the stakeholders and they can change during the process. The output is a specification of functional and non-functional requirements.

Design phase

• Describe in detail how the system will meet the requirements specified earlier and specify the plans for implementing and testing the system. The final output will be a document describing the system requirements, operating environment, database design, user interface, and processing logic.

Development phase

• The system is actually constructed, so the software is written, databases are created, and the hardware is installed. The new system has to be integrated with the old one. In this phase, the testing happens to check and fix eventual errors. The outcome will be the software, data, and files for testing.

Implementation phase

• Make the system operational in the production environment. Support because of the new system, implementation schedule, and recommendation for future improvements are all tasks of this phase. The outcome of this step is the system itself, installed and running correctly. To change from an existing system to a new one, there are different methods like direct changeover.