Sviluppo dei sistemi di informazione: Appunti di Sistemi

Chapter 10. Developing Information Systems TIME, COST QUALITY

Every software development projects faces a tension among and and they imply a tradeoff 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)

(SOFTWARE to plan, structure and control the software development project. The

framework can be unique for the entire organization otherwise can be different depending on the projects.

SYSTEM DEVELOPMENT LIFE CYCLE (SDLC)

The traditional approach is the that provides a disciplined approach to system

development. This kind of approach is a waterfall method since the result of one phase flow 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 on the

project. There are different aspects of feasibility as technical, economic (system affordable and worth),

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 NONFUNCTIONAL

(how the system should interact with users and other systems) and (the

REQUIREMENTS ELICITATION

constraints of the system). The main task of this phase is the that is to gather

requirements from the stakeholders and they can change during the process. .

The output is a specification of F and NF req

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, database are created and

the hardware is installed. The new system has to be also integrated with the old one. In this phase also 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

DIRECT CHANGEOVER

to a new one there are different methods like: (old system no longer used and

PARALLEL OPERATION

immediately replaced // low time, high risk), (both new and old operate together // low

PHASED IMPLEMENTATION PILOT

risk, high cost and time), (new system is implemented in stages) and

OPERATION (new system is implemented in a business unit or location and then in the entire organization).

MAINTAINANCE PHASE

- = longest and most costly phase that ensures the system to operate correctly. This phase

involves fixing any problems and modifying or adding to the programs to meet new needs.

Alternative methodologies to approach the development of a new system are:

PROTOTYPING

- = it is an iterative process that begins with an investigation of the main requirements of the

system. Following, a prototype (a rough version of the system) is made and reviewed by the stakeholders. If the

system shows problems, a new prototype is made fixing the flaws otherwise the prototype is implemented fully.

It has advantages as more stakeholders’ involvement and more effective for uncovering system requirements

but it has drawbacks like poorly designed systems when scaled up, difficult to estimate time and so costs.