Unit 4
Computer software system
A computer cannot do anything on its own. We need to give instructions to it to
make it do a job desired by us. Hence, it is necessary to specify a sequence of
instructions a computer must perform to solve a problem. Such a sequence of
instructions written in a language understood by a computer is called a computer
program. A program controls a computer’s processing activity, and the computer
performs precisely what the program wants it to do. When a computer is using a
program to perform a task, we say, it is running or executing that program. The
term software refers to a set of computer programs, procedures, and associated
documents (flowcharts, manuals, etc.) describing the programs, and how they are
to be used.
Software development process
Software Development Life Cycle (SDLC) is a process used by the software
industry to design, develop and test high quality software. The SDLC aims to
produce high quality software that meets customer expectations. It covers the
detailed plan for building, deploying and maintaining the software.
Software development for business applications is not an easy task. In developing a
large software (e.g., MIS), many people are involved and many months or even
years are spent. However, a small application (e.g., Payroll) can be developed in
few weeks or months by a single or few programmers. For such small systems,
software development activities may be done implicitly without proper
documentation. But, for large systems, these activities must be done explicitly with
proper planning and documentation. Whether a system is small or large, software
development revolves around a life cycle that begins with the recognition of users'
needs and understanding their problem. A plan is made for solving the problem
and then a sequence of activities are performed step by step. The basic activities or
phases, that are performed for developing a software are:
,1. Requirement Specification
2. System Analysis and Design
3. Implementation (also known as Construction or Code Generation)
4. Testing and Debugging
5. Deployment (also known as Installation)
6.Maintenance
Development process proceeds from one phase to the next in a purely sequential
manner. Hence, the next phase in the life cycle starts only after the defined set of
goals are achieved for its previous phase and it is completed fully, perfected, and
frozen. This model is also known as waterfall model because it is a sequential
development process, which flows steadily downwards (like a waterfall) through
the various phases of the process.
1. Requirement specification. The team defines all possible requirements of the
software in this phase. These include functionality, capability, performance, user
interface, inputs, and outputs requirements. The team records the defined
requirements in a requirement specification document.
, 2. System analysis and design. The team studies the requirements specified in the
first phase with respect to available hardware and software technologies and
prepares a system design document. The system design document defines the
overall system architecture. It specifies the various hardware and software
components of the system and the interfaces between the components
3. Implementation. This phase is also known as construction or code generation
because in this phase, the team constructs (codes in selected programming
languages) the various software components specified in the system design
document. To construct a software component, the team first divides it into
modules, and then codes each module separately. The team codes and tests each
module independently. This type of testing of a module done by the programmer
who developed the module is referred to as unit testing.
4. Testing and debugging. In this phase, the team integrates the independently
developed and tested modules into a complete system. The team then tests the
integrated system to check if all modules coordinate properly with each other and
the system as a whole behaves as per the specifications. They debug (correct) any
bug (error) that they find during integrated system testing, and repeat testing of that
functionality of the system. After the team completes this phase, the software is
ready for release and deployment.
5. Deployment. Once the team tests the software and removes all known errors, the
team deploys the software at user(s) site on associated hardware for use by the
intended user(s). The team also evaluates the system against the specified
requirements in this phase.
6. Maintenance. Some problems with the system, which the team is unable to find
during various phases of the development life cycle of the system, surface only
after the team deploys the system and puts it in operation. The team fixes these
problems in the system in its maintenance phase. Additionally, the team needs to
make changes in the system from time-to-time to take care of new user
requirements, changes in technology, changes in organizational policies, etc.
