Friday 8 August 2014

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.

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


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