Software Life Cycle

Software Life Cycle 
                           (or)
                 Software Development Life Cycles(SDLC)

• Software life cycle (or software process):

-        series of identifiable stages that a software product undergoes during its life time:

*        Feasibility study

*        requirements analysis and specification,

*        design,

*        coding,

*        testing

*        maintenance

Explain about Feasibility study?

Ans: Feasibility Study

• Main aim of feasibility study:determine whether developing the product

-         financially worthwhile

-         technically feasible.

• First roughly understand what the customer wants:

-        different data which would be input to the system,

-        processing needed on these data,

-        output data to be produced by the system,

-        various constraints on the behavior of the system.

Activities during Feasibility Study

• Work out an overall understanding of the problem.
• Formulate different solution strategies.
• Examine alternate solution strategies in terms of:

*        resources required,

*        cost of development, and

*        development time.

• Perform a cost/benefit analysis:
• to determine which solution is the best.
• you may determine that none of the solutions is feasible due to:

high cost,

resource constraints,

technical reasons.

Explain about Requirements Analysis and Specification?

• Aim of this phase:

-         understand the exact requirements of the customer, 

-         document them properly.

• Consists of two distinct activities:

-         requirements gathering and analysis

-         requirements specification.

Goals of Requirements Analysis

• Collect all related data from the customer:

-         analyze the collected data to clearly understand what the customer wants,

-         find out any inconsistencies and incompleteness in the requirements,

-         resolve all inconsistencies and incompleteness.

Requirements Gathering

• Gathering relevant data:

-         usually collected from the end-users through interviews and discussions.

-         For example,  for a business accounting software:

*         interview all the accountants of the organization to find out their requirements.

• The data you initially collect from the users:

-         would usually contain several contradictions and ambiguities:

-         each user  typically has only a partial and incomplete view of the system.

• Ambiguities and contradictions:

-         must be identified

-         resolved by discussions with the customers.

• Next, requirements are organized:

-         into a Software Requirements Specification (SRS) document.

• Engineers doing requirements analysis and specification:

-         are designated as  analysts.  

Explain about Design?

• Design  phase transforms  requirements  specification:

-          into a  form suitable for implementation in some programming language.

• In technical terms:

-         during design phase,  software architecture is derived from the SRS document. 

• Two design approaches:

-         traditional approach,

-         object oriented approach.

Traditional Design Approach

• Consists of  two activities:

-         Structured analysis

-         Structured design

Structured Analysis Activity

• Identify all the functions to be performed.
• Identify data flow among the functions.
• Decompose each function  recursively into sub-functions. 

-         Identify data flow among the  sub functions as well.

• Carried out using Data flow diagrams (DFDs).
• After structured analysis, carry out structured design:

-         architectural design (or high-level design)

-         detailed design (or low-level design).

Structured Design

• High-level design: 

-         decompose the system into modules, 

-         represent invocation relationships among the modules.

• Detailed design:

-         different modules designed in greater detail:

*         data structures and algorithms for each module are designed.

Object Oriented Design

• First identify various objects (real world entities)  occurring in the problem:

-         identify the relationships among the objects.

-         For example, the objects in a pay-roll software may be:

*         employees,

*         managers,

*         pay-roll register,

*         Departments, etc.

• Object structure

-         further refined to obtain the detailed design.

• OOD has several advantages:

-         lower development effort,

-         lower development time,

-         better maintainability.

Explain about Implementation?

• Purpose of implementation phase (aka coding and unit testing phase):

-         translate(converting) software design into source code.

• During the implementation phase:

-         each module of the design is  coded,

-         each module is unit tested

·         tested independently as a stand alone unit, and debugged,

-         each module is documented.

• The purpose of  unit testing:

-         test if individual modules work correctly. 

• The end product of implementation  phase:

a set of program modules that have been  tested individually.

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Life Cycle Model

                                                   **********************

Before learning Life Cycle Models first lets we discuss environment in the Software Organisations.

                                            Designation in Software Organisations

• Whenever we enter into the software organisation as a Trainee(fresher)
• after some couple of time we will be Software Engineer
• later Senior Software engineer
• After gaining Experience we may become as a Tech Lead/Team Lead./Module Leader
• Next designation is we have choice either we may try for Project Manager or Business Analysists
• BA(Business Analysists) involves in the Analysis phase

• A software life cycle model (or  process model):

-        a descriptive and diagrammatic model of software life cycle:

-        identifies all the activities required for product development,

-        establishes a precedence ordering among the different activities,

-        Divides life cycle into phases. 

• Several different activities may be carried out in each life cycle phase.

-        For example, the design stage might consist of:

*        structured analysis activity followed by 

*        structured design activity.

Why Model  Life Cycle ?

Ans:

• A written description:

-        forms a common understanding of activities among the software developers.

-        helps  in identifying inconsistencies, redundancies, and omissions in the development process.

-        Helps in tailoring a process model for specific projects.

• Processes are tailored for special projects.

-        A documented process model

·         helps to identify where the tailoring is to occur.

• The development team must identify a suitable life cycle model:

-        and then adhere to it.

-        Primary advantage of adhering to a life cycle model:

·        helps development of software in a systematic and  disciplined manner.

• When a program is developed by a single programmer ---

-        he has the freedom to decide his exact steps.

• When a software product is being developed by a team: 

-        there must be a precise understanding among team members as to when to do what,

-        otherwise it would lead to chaos and project  failure.

• A software project will never succeed if:

-        one engineer starts writing code,

-        another concentrates on writing the test document first,

-        yet another engineer first defines the file structure

-        another defines the I/O for his portion first.

• A life cycle model:

-        defines  entry and exit criteria for every phase.

-        A phase is considered to be complete:

·        only when all its exit criteria are satisfied.

• The phase exit criteria for the software requirements specification phase:

-        Software Requirements Specification (SRS) document is complete, reviewed, and approved by the customer.

• A phase can start:

-        only if its phase-entry criteria have been satisfied.

• It becomes easier for software project managers:

-        to monitor the progress of the project.

• When a life cycle model is adhered(undertaken) to,

-        the project manager can at any time fairly accurately tell,

·        at which stage  (e.g., design, code, test, etc. ) of the project is.

-        Otherwise, it becomes very difficult to track the progress of the project 

·        the project manager would have to depend on the guesses of the team members.

• This usually leads to a problem:

-        known as the  99% complete syndrome.

• Many life cycle models have been proposed.
• We will confine our attention to a few important and commonly used models.

-        classical waterfall model

-        iterative waterfall,

-        evolutionary,

-        prototyping, and

-        spiral model