system development life cycle

Software / Systems Development Life
Cycle (SDLC)
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INTRODUCTION TO SDLC
 Systems Development Life Cycle (SDLC) is a logical process used by
the software industry to develop software with the highest quality and
lowest cost in the shortest time. SDLC includes a detailed plan for how
to develop, alter, maintain, and replace a software system.
 The SDLC aims to produce a high-quality software that meets or
exceeds customer expectations.
 From the inception of an idea for a software system, until it is
implemented and delivered to a customer the system undergoes
gradual development and evolutions.
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 Software is said to have a life cycle. Related activities in the life cycle
are combined into phases, called the lifecycle phases.
 The activities that must be performed throughout the systems
development life cycle and the sequence in which they are performed
are well identified.
 Each of these phases results in the development of either a part of the
system or something associated with the system.
 Each phase has well-defined starting and ending points, with clearly
identifiable deliverables to the next phase.
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 SDLC should result in a high quality system
 within time and cost estimates
 works effectively and efficiently in the current and planned Information
Technology infrastructure
 Cheap to maintain.
 Although there is general agreement about what needs to be done different
authors name individual steps and deliverables differently.
 Phases are not necessarily sequential
 Each phase has a specific outcome and deliverable required by the next
phase in the life cycle
 Individual companies use customized life cycles. 4

 Strength:
o Monitoring large projects.
o Explain step by step.
o Sufficient documentation is provided.
o Ease of maintenance
 Weakness:
o Need more time for development
o Development cost is more
o Sometimes user input is limited.
o Difficult to estimate cost.
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It consists of six phases namely:
1.System Planning (Initiation and Feasibility Study)
2.System Analysis (Requirements Analysis and Project Planning)
3.System Design
4.System Coding (Implementation)
5.System Testing
6.Deployment and Maintenance
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Software Development Life Cycle (SDLC)

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Software Development Life Cycle (SDLC)

System Planning
 This phase involves two steps: Recognition of need (Initiation Stage)
and the Feasibility Study.
 The initiation phase may begin in many different ways:
 A user may face a problem in the current system (manual or already
computerized) and hence recognizes a need for improving an
information system
 A user may work with the IS staff to produce a written request to
study a particular business problem.
 The IS staff may discover an opportunity to use information systems
beneficially and then try to interest users.
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System Planning
 A top manager may notice a business problem and ask the head of
IS to look into it.
 A computer crash or other operational problem may reveal a major
problem that can be patched temporarily but requires a larger project
to fix it completely.
 After recognizing the need, a formal request is made to the organization
either for a new system or modifying the current system.
 System Analyst receives the request and he begins preliminary
investigations to determine whether the system requested is feasible to
develop or not.
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System Planning
 During preliminary investigations, the analyst understands the major
requirements of the system by meeting with the users, asking a number
of questions regarding the current working system, problems of the
current system and their present needs.
Feasibility Study.
A system’s feasibility is typically considered from the following viewpoints:
o Operational Feasibility
o Economic Feasibility
o Technical Feasibility
o Legal/Political Feasibility
o Organizational Feasibility
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System Planning
Operational Feasibility
 How well does the proposed system solve the problems
 How does it fit in the existing business environment and objectives with
regard to development schedule, delivery date, corporate culture and
existing business processes.
Economic Feasibility
 Can the firm afford to build the system
 Do its benefits exceed its costs
 Does it have a higher priority than other projects that need the same
resources.
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System Planning
Technical Feasibility.
 Does the technology needed for the system exists
 Does the firm have enough experience using that technology.
Organizational feasibility
 Does the system have enough support to be implemented successfully
 Does it bring excessive amount of change
 Is the organization changing too rapidly to absorb it.
Legal feasibility
 Does the proposed system conflict with legal requirements
 Is the proposed system acceptable in accordance to the laws of the
land.
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System Planning
At first the Project Managers or team leaders visit the client side to:
1. Study different input data to the system and output data to be
produced by the system.
2. Study the type of processing needed and the various constraints on
the behavior of the system
3. Investigate the different solutions that are possible considering the
resources required, the cost of development and the development
time for each solution.
4. Pick the best solution depending on the customer budget and
availability of the technical expertise in the area of development.
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System Planning
 The project plan breaks the project into sub-projects with start and
completion times. It also identifies staffing, resource requirements, and
dependencies between project steps.
 The functional specification is approved by both user and IS personnel.
It clarifies the purpose and scope of the proposed project by describing
the business processes that will be affected and how they will be
performed using the system.
 Functional specifications do not explain exactly what data, reports, or
data entry screens will be included. This more detailed description is
produced in the development phase.
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System Planning
 In brief the Feasibility Study consists of statement of the problem,
summary of findings and recommendations, details of findings, and
recommendations and conclusions.
 After analyzing this data one of three choices will be taken:
 develop a new system
 improve the current system
 leave the system as it is
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System Analysis
This phase, also called the Requirements Analysis stage includes:
(i) Studying and understanding the existing system in detail (Problem
Analysis). “What don’t we want?”
 This involves identifying pros and cons of the current system in-
place, so as to carry forward the pros and avoid the cons in the new
system.
 It involves getting input from all stakeholders, including customers,
salespeople, industry experts, and programmers to help in learning
the strengths and weaknesses of the current system with
improvement as the goal
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System Analysis
(ii) Collecting data in order to find out the requirements of the
users.(Requirements Specification). “What do we want?”
 This phase is the main focus of the project managers, stake holders
and the users. The team defines the requirements of the new
software like:
 What will the System do?
 Who is going to use the system?
 How will they use the system?
 What data should be input into the system?
 What data should be output by the system?
 Where and When will the system be used?
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System Analysis
 The team also determines the cost and resources required, and it also
details the risks involved and provides sub-plans for softening those
risks.
 The gathered requirements are analyzed for their validity and the
possibility of incorporating them in the proposed system is also
studied.
 Every stakeholder should understand the scope of the work and how
each requirement is going to be fulfilled.
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System Analysis
The tools used to collect data and information during analysis include:
 Data flow diagrams
 Interviews,
 On-site observations
 Questionnaires.
 A Software Requirement Specification (SRS) document is finally
created where the analyst specifies all the requirements specifications
to be used in guiding the next phases.
 The important components of this document are functional
requirements, the nonfunctional requirements, and the goals of
implementation.
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System Design
“How will we get what we want?”
 The term design describes a final system and the process by which it is
developed. The major objective of this phase is to produce the best
model of the system based on the requirements specified in SRS
 A logical design of the system is developed which basically answers the
question as to what has to be done. On the contrary the physical design
specifies as to how it will be done.
 System Design helps in specifying hardware and system requirements
and also helps in defining overall system architecture.
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System Design
 The first step in system design is to determine the outputs to be
produced and in what format.
 Then, input data and master files (data base) have to be designed to
meet the requirements of the output.
 And finally, the operational (processing) phase handled through program
construction and testing, including a list of the programs needed to meet
the system‘s objectives and complete documentation.
 The design is usually kept in the Design Specification Document
(DSD)
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System Design
 Usually more than one design approach is proposed and documented in
a DSD. All the different designs are reviewed by all the important
stakeholders and based on various parameters as risk assessment,
product robustness, design modularity, budget and time constraints, the
best design approach is selected for the product.
 The design clearly defines all the architectural modules of the product
along with its communication and data flow representation with the
external and third party modules (if any).
 Two distinctly different approaches are available:
The traditional Structured Analysis Design approach and
The object-oriented design approach.
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System Design
Traditional Structured design approach
 A structured analysis of the requirements specification is carried out and
this is followed by a structured design activity. During structured design,
the results of structured analysis are transformed into the software
design.
Object-oriented design approach
 The various objects that occur in the problem domain and the solution
domain are first identified, and the different relationships that exist
among these objects are identified. The object structure is further
refined to obtain the detailed design.
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System Coding
“Let’s create what we want.”
 When the design is accepted by the organization, the analyst begins
developing the software using a programming language.
 This is the phase when the programmers play their role in development
of the system.
 Developers must follow the coding guidelines defined by their
organization and programming tools like compilers, interpreters,
debuggers, etc. are used to generate the code. Different high level
programming languages such as C, C++, Pascal, Java and PHP are
used for coding. The programming language is chosen with respect to
the type of software being developed.
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System Coding
 This phase can be categorized into two sub-phases:
 Database Design and
 Program Design
 Database design deals with the aspect of developing the databases.
 Program Design deals with writing of programs(coding),editing of
programs using a text editor or word processor and finally testing them.
 Each module is tested in isolation as this is the most efficient way to
debug the errors identified at this stage.
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System Testing
“Did we get what we want?”
 This stage is usually a subset of all the stages as in the modern SDLC
models, the testing activities are mostly involved in all the stages of
SDLC.
 However, this stage refers to the testing only stage of the product where
product defects are reported, tracked, fixed and retested, until the
product reaches the quality standards defined in the SRS.
 During testing, experienced testers use different techniques to test the
system against the requirements to ensure that the system is bug free.
 The testers aim to find defects within the system as well as verifying
whether the application behaves as expected and according to what was
documented in the requirements analysis phase.
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System Testing
 Once a defect is found, testers inform the developers about the details
of the issue and if it is a valid defect, developers will fix and create a new
version of the software which needs to be verified again.
 This cycle is repeated until all requirements have been tested and all the
defects have been fixed.
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System Testing
 System testing usually consists of three different kinds of testing
activities:
 α - testing: It is the system testing performed by the development
team.
 β - testing: It is the system testing performed by a friendly set of
customers.
 Acceptance testing: It is the system testing performed by the
customer himself after the product delivery to determine whether to
accept or reject the delivered product.
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System Testing
 Integration of different modules is undertaken once they have been
coded and unit tested. Integration is normally carried out incrementally
over a number of steps.
 When all the modules have been successfully integrated and tested,
system testing is carried out.
 System testing ensures that the developed system conforms to its
requirements laid out in the SRS document.
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Deployment and Maintenance
Deployment
“Let’s start using what we got.”
 The Deployment stage is concerned with user training, site
preparation, and file conversion.
 System testing checks the readiness and accuracy of the system to
access, updates, and retrieve data from the old files. Once the
programs become available, test data are read into the computer and
processed against the files provided for testing. If successful, the
program(s) is then run with actual data.
 The new system runs simultaneously with the old system to enable
the staff gain experience and learn the new system.
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Deployment and Maintenance
Maintenance
This involves performing any one or more of the following three activities:
1. Corrective Maintenance: Correcting errors that were not discovered
during the product development phase .
2. Perfective Maintenance: Improving the implementation of the system,
and enhancing the functionalities of the system according to the
customer’s requirements.
3. Adaptive Maintenance: Porting the software to work in a new
environment.
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Post-implementation and maintenance
“Let’s get this closer to what we want.”
 In the final stage of SDLC, the software that is developed is given to the
users. Periodic maintenance of hardware and software is carried out to
have a successful and trouble free working of the system
 It is obvious that changes occur once the project is handed over to the
end user. The software operation must not be affected by any changes.
The developers must develop the project in such a way that it is
adaptable to those changes.
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system development life cycle

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