System development involves the use of various methodologies, models, tools and techniques to build and implement an information system. Models used to develop a system include flow charts, data flow diagrams (DFD) and entity-relationship diagrams (ERD); models used to manage the development process include PERT and Gantt charts. Tools that help build a system include project management applications, drawing/graphics applications, word processors, IDEs, DBMS and CASE tools.
The SDLC is a structured, step-by-step approach used to develop and implement a new system, typically represented in six phases:
a. Planning phase
Discovers, identifies and defines the scope of the project: defining the problem/opportunity in unambiguous terms, assessing initial feasibility, and preparing a project plan.
b. Analysis phase
Investigates how the current system works (if it exists) and identifies weaknesses and opportunities to improve, using techniques such as data flow diagrams, interviews, questionnaires and observation. Activities: creating a logical model of the new system, specifying inputs/processing/outputs, preparing an implementation plan, and specifying performance criteria.
c. Design phase
Generates several alternative technical solutions for the new logical model: selecting the best technical alternative, developing detailed software specifications, and creating a detailed physical model.
d. Development phase
Actually creates the new system: acquiring and installing hardware, writing software, and testing it using integration testing (does everyone in the organization use the software correctly), acceptance testing (users verify it works under operational conditions) and beta testing (a limited audience of external users).
e. Implementation phase
Trains users, converts existing information to the new system, and carries out acceptance testing. Four conversion methods are commonly used:
- Parallel conversion: both old and new systems run until the new system is proven – safest, but expensive.
- Plunge (direct) conversion: the old system is unplugged and the new system used exclusively – high risk.
- Pilot conversion: only a selected group of users converts to the new system before the rest of the organization.
- Piecemeal conversion: only a portion of the new system runs at first, with the rest converted once it works correctly.
f. Support and maintenance
The organization provides a formal mechanism for periodic review of the system, users may suggest changes, and the organization evaluates which changes to undertake.
Some Popular SDLC Models
- Waterfall model: a breakdown of activities into linear sequential phases, where each phase depends on the deliverables of the previous one.
- Iterative model: focuses on an initial simplified implementation that iteratively enhances the evolving versions until the system is complete.
- V-shape model: an extension of the waterfall model where the process steps bend upwards to form a V shape.
- Prototyping: a prototype is built, tested and reworked as necessary until an acceptable outcome is achieved.
