Software development life_cycleDocument Transcript
Software Development Life Cycle
The software Life Cycle encompasses all activities required to define, develop, test
deliver, operate and maintain a software product. Planning the software development
process involves several important considerations. The first is to define a product life
cycle model. The SDLC activities are:
1. Feasibility: Determine if the software has significant contribution to business. It
includes market analysis if similar software is in demand in market. Software is
evaluated on the basis of cost, schedule and quality.
2. Requirements are determined such as functional properties desired by users,
system requirements such as availability, performance and safety, establishing set
of objectives the system should meet, characteristics that the system should not
exhibit. Such requirements are obtained by various methods such as interviews,
communication with stake holders, scenario discussions, use cases and
ethnography. These requirements are then verified and tested.
3. Project Planning, cost analysis, scheduling, quality assurance plans are made
4. Designing i.e. Architectural design, Interface design and detailed design
5. Implementation includes writing the code for the project as per the designs and
6. Testing ensures accuracy and reliability
7. Delivery, Installation, Training, Help Desk
8. Maintenance, software configuration management.
Another view of SDLC emphasizes the milestone, documents and reviews throughout
product development. It is difficult for project managers to assess progress or anticipate
problems. Establishing milestones, improves product visibility. The following are the
milestones for the project.
1. Feasibility report
2. System definition, project plan
3. Software requirement specification, Preliminary user manual
4. Architectural design document
5. Detailed design document
6. Software verification plan
7. Product Schedule
8. Software test plan, Acceptance test
9. Software quality assurance plan
10. User manual
11. Source code
12. Test results
13. Defect report
Every software engineering organization should describe a unique set of framework
activities for the software process it adopts. Various models have been developed over
the years to accommodate these activities.
Models for Software Development
1. Waterfall Model suggests a systematic sequential approach to software
development that begins with customer specification of requirements. The
principle stages of the model map onto fundamental development activities.
a. Requirement Analysis and definition
b. System and software design
c. Implementation and unit testing
d. Integration and system testing
e. Operation and maintenance
The verification at each stage ensures that the output is consistent with its input and
overall requirement of the system. These outputs are often called work products and can
be listed as:
a. Requirements documents
b. Project plan
c. Design documents
d. Test plan and test reports
e. Final code
f. Software manuals (e.g. user, installation, etc)
1. Simple method with clear steps
2. Easy to administer as it is systematic
3. Verification at each stage ensures early detection of errors / misunderstanding
4. Documentation helps in future maintenance and revisions
1. Unchanging requirements are not realistic
2. Document driven process
3. Change adaptability is very slow
2. Incremental Model: Customer identifies the services to be provided. The delivery
increments are then defined, with each increment providing a sub-set of the
system functionality. Once the system increments for the services have been
identified, the requirements to be delivered in the first increment are defined in
detail and the increment is developed.
Define Assign Design Develop
outline requirements System System
requirement to increments Architecture increment
Validate Integrate Validate
Increment Increment System Final System
3. Prototyping: First a working prototype of the software is developed instead of
developing the actual software. The developers use this prototype to refine the
requirements and prepare final specification document. After the finalization of
SRS document, the prototype is discarded and actual system is then developed
using the waterfall approach.
Quick Design / Prototype
Customer Evaluation Requirements as per
Implementation and Unit Testing
Integration and System Testing
Operation and Maintenance
There are 2 types of prototypes; throw-away, where the initial prototype is
discarded after the requirements are defined and the evolutionary prototype,
where the system is built further on the prototype itself. A prototype is built for
those requirements which are critical for the project and are not understood well.
If the number of requirements which need clarification is more, then a working
prototype is built for them. The importance or criticality of such requirements is
also a significant factor in determining the need of a prototype.
Advantages of Prototyping
1. Users are actively involved in the development
2. It provides a better system to users, as users have natural tendency to change
their mind in specifying requirements and this method of developing systems
supports this user tendency.
3. Since in this methodology a working model of the system is provided, the
users get a better understanding of the system being developed.
4. Errors can be detected much earlier as the system is mode side by side.
5. Quicker user feedback is available leading to better solutions.
1. Leads to implementing and then repairing way of building systems.
2. Practically, this methodology may increase the complexity of the system as
scope of the system may expand beyond original plans.
4. Spiral Model: Boehm tried to incorporate the ‘project risk’ factor into a life cycle
model. Each phase is split roughly into four sections namely planning, risk
analysis, development and assessment. There are 4 phases namely feasibility,
requirements analysis, design and coding and testing.
The development spiral consists of four quadrants as shown in the figure above
The first step in each phase is to identify the objective, alternatives and constraints of that
phase. The next stage involves identifying the best alternative, by comparing all and
performing risk analysis. One the alternative is chose, prototypes are built using
simulation and benchmarks. Each phase is completed with a review by the people
concerned with the project.
Specialized process models
1. Extreme programming includes creating a set of stories and assigning their
priority. The commitment defines the order for development. The objects are
organized for development. Designing occurs both after and before programming,
in the form of design and refactoring. Programming happens in the form of pain
programming where two people work together at one workstation. Writing test
cases before starting the coding is a key feature of extreme programming.
Acceptance testing is followed by system testing.
2. Component-Based Development uses commercial-off-the-shelf (COTS) software
3. Unified Process is a use-case driven, architecture centric, iterative and
incremental software process.
4. Dynamic Systems Development Method (DSDM) suggests an iterative software
process. After the feasibility study follows the business study that establishes the
functional and information requirements for the application. The iteration steps
include Functional model iteration which creates a prototype. New requirements
might be generated through the prototype, by the user. Subsequently or
simultaneously designs are built or rebuilt. Implementation iteration places the
latest software increments.
5. Feature driven development emphasizes project management guidelines and
techniques. The processes defined for such development are to develop an overall
model, build a feature list, plan by feature, design by feature, build by feature..
Process improvement is about understanding existing processes and introducing
process changes to improve product quality reduce costs or accelerate schedules.
Most process improvement work so far has focused on defect reduction. This reflects
the increasing attention paid by industry to quality. However, other process attributes
can also be the focus of improvement. Feedback is important for process
improvement to initiate.
Why is it difficult to improve a software process?
1. Not enough time: Developers, because of unrealistic schedules are left with no
time to explore problems of development and find solutions.
2. Lack of knowledge: many developers are not aware of best practices
3. Wrong motivation: The basic motivation should be to eradicate current difficulties
and not just to achieve a higher CMM level.
4. Insufficient commitment
Begins Improved future state
Do not quit here
Process improvement stages
Attributes of the current process are measured. These are a baseline for
The current process is assessed and bottlenecks and weaknesses are identified.
Changes to the process that have been identified during the analysis are
Process used should depend on type of
product which is being developed
• For large systems, management is usually the principal problem so you
need a strictly managed process;
• For smaller systems, more informality is possible.
There is no uniformly applicable process which
should be standardised within an organisation
• High costs may be incurred if you force an inappropriate process on a
• Inappropriate methods can also increase costs and lead to reduced quality.
Process analysis and modelling
1. Study an existing process to understand its activities.
2. Produce an abstract model of the process. You should normally represent this
graphically. Several different views (e.g. activities, deliverables, etc.) may be
3. Analyse the model to discover process problems. This involves discussing process
activities with stakeholders and discovering problems and possible process
Process analysis techniques
• Published process models and process standards: It is always best to start
process analysis with an existing model. People then may extend and change
• Questionnaires and interviews: Must be carefully designed. Participants may
tell you what they think you want to hear.
• Ethnographic analysis: Involves assimilating process knowledge by
observation. Best for in-depth analysis of process fragments rather than for
Process change stages
• Improvement identification.
• Improvement prioritization.
• Process change introduction.
• Process change training.
• Change tuning.