Lect-4: Software Development Life Cycle Model - SPM

Lecture-4
Software Development Life
Cycle (SDLC) Models
Mr. Mubashir Ali
Lecturer(Dept. of Computer Science)
dr.mubashirali1@gmail.com

SDLC Model
A framework that describes the activities
performed at each stage of a software
development project.

Capability Maturity Model
(CMM)
• A bench-mark for measuring the maturity
of an organization’s software process
• CMM defines 5 levels of process maturity
based on certain Key Process Areas (KPA)

CMM Levels
Level 5 – Optimizing (< 1%)
-- process change management
-- technology change management
-- defect prevention
Level 4 – Managed (< 5%)
-- software quality management
-- quantitative process management
Level 3 – Defined (< 10%)
-- peer reviews
-- intergroup coordination
-- software product engineering
-- integrated software management
-- training program
-- organization process definition
-- organization process focus
Level 2 – Repeatable (~ 15%)
-- software configuration management
-- software quality assurance
-- software project tracking and oversight
-- software project planning
-- requirements management
Level 1 – Initial (~ 70%)

Life Cycle Model
 It provides a fixed generic framework that can be tailored to a
specific project.
 Project specific parameters will include:
 Size, (person-years)
 Budget,
 Duration
project plan = lifecycle model + project parameters

By changing the lifecycle model, we can
Improve
• Development speed (time to market)
• Product quality
• Project visibility
• Administrative overhead
• Risk exposure
• Customer relations, etc, etc.

The Waterfall Model
The waterfall model is the classic lifecycle model
It is widely known, understood and (commonly?) used.
In some respect, waterfall is the ”commonsense” approach.
Introduced by Royce in 1970.

Waterfall Model
• Requirements – defines needed
information, function, behavior,
performance and interfaces.
• Design – data structures, software
architecture, interface
representations, algorithmic details.
• Implementation – source code,
database, user documentation,
testing.

Waterfall Strengths
• Easy to understand, easy to use
• Provides structure to inexperienced staff
• Milestones are well understood
• Sets requirements stability
• Good for management control (plan, staff, track)
• Works well when quality is more important than cost or
schedule

Waterfall Deficiencies
1. Idealised, does not match reality well.
2. Doesn’t reflect iterative nature of exploratory development.
3. Unrealistic to expect accurate requirements so early in
project
4. Software is delivered late in project, delays discovery of
serious errors.
5. Difficult to integrate risk management
6. Difficult and expensive to make changes to documents,
”swimming upstream”.
7. Significant administrative overhead, costly for small teams
and projects.

When to use the Waterfall
Model
• Requirements are very well known
• Product definition is stable
• Technology is understood
• New version of an existing product
• Porting an existing product to a new platform.

V-Shaped SDLC Model
• A variant of the Waterfall
that emphasizes the
verification and validation
of the product.
• Testing of the product is
planned in parallel with a
corresponding phase of
development

V-Shaped Steps
• Project and Requirements
Planning – allocate resources
• Product Requirements and
Specification Analysis –
complete specification of the
software system
• Architecture or High-Level
Design – defines how software
functions fulfill the design
• Detailed Design – develop
algorithms for each
architectural component
• Production, operation and
maintenance – provide for
enhancement and corrections
• System and acceptance
testing – check the entire
software system in its
environment
• Integration and Testing – check
that modules interconnect
correctly
• Unit testing – check that each
module acts as expected
• Coding – transform algorithms
into software

V-Shaped Strengths
• Emphasize planning for verification and
validation of the product in early stages
of product development
• Each deliverable must be testable
• Project management can track progress
by milestones
• Easy to use

V-Shaped Weaknesses
• Does not easily handle concurrent events
• Does not handle iterations or phases
• Does not easily handle dynamic changes in
requirements
• Does not contain risk analysis activities

When to use the V-Shaped Model
• Excellent choice for systems requiring high reliability –
hospital patient control applications
• All requirements are known up-front
• Solution and technology are known

Structured Evolutionary
Prototyping Model
• Developers build a prototype during the requirements
phase
• Prototype is evaluated by end users
• Users give corrective feedback
• Developers further refine the prototype
• When the user is satisfied, the prototype code is
brought up to the standards needed for a final product.

Prototyping Steps
• A preliminary project plan is developed
• An partial high-level paper model is created
• The model is source for a partial requirements
specification
• A prototype is built with basic and critical attributes
• The designer builds
– the database
– user interface
– algorithmic functions
• The designer demonstrates the prototype, the user
evaluates for problems and suggests improvements.
• This loop continues until the user is satisfied

Prototyping Strengths
• Customers can “see” the system requirements as they are being gathered
• Developers learn from customers
• A more accurate end product
• Unexpected requirements accommodated
• Allows for flexible design and development
• Steady, visible signs of progress produced
• Interaction with the prototype stimulates awareness of additional needed
functionality

Prototyping Weaknesses
• Tendency to abandon structured program development
for “code-and-fix” development
• Bad reputation for “quick-and-dirty” methods
• Overall maintainability may be overlooked
• The customer may want the prototype delivered.
• Process may continue forever (scope creep)

When to use
Structured Evolutionary Prototyping
• Requirements are unstable or have to be clarified
• As the requirements clarification stage of a waterfall model
• Develop user interfaces
• Short-lived demonstrations
• New, original development
• With the analysis and design portions of object-oriented
development.

Rapid Application Model
(RAD)
• Requirements planning phase (a workshop utilizing structured
discussion of business problems)
• User description phase – automated tools capture information from
users
• Construction phase – productivity tools, such as code generators,
screen generators, etc. inside a time-box. (“Do until done”)
• Cut over phase -- installation of the system, user acceptance
testing and user training

RAD Strengths
• Reduced cycle time and improved productivity with fewer people
means lower costs
• Customer involved throughout the complete cycle minimizes risk of
not achieving customer satisfaction and business needs
• Focus moves from documentation to code (WYSIWYG).
• Uses modeling concepts to capture information about business,
data, and processes.

RAD Weaknesses
• Accelerated development process must give quick responses to the
user
• Risk of never achieving closure
• Hard to use with legacy systems
• Developers and customers must be committed to rapid-fire
activities in an abbreviated time frame.

When to use RAD
• User involved throughout the life cycle
• Project can be time-boxed
• Functionality delivered in increments

Timeboxing is a Planning technique common in planning projects (typically for
software development), where the schedule is divided into a number of
separate time periods (timeboxes, normally two to six weeks long), with each
part having its own deliverables, deadline and budget. Timeboxing is a core
aspect of rapid application development (RAD) software development
processes such as dynamic systems development method (DSDM) and agile
software development.
Timeboxes are used as a form of risk management, especially for tasks that
may easily extend past their deadlines. The end date (deadline) is one of the
primary drivers in the planning and should not be changed as it is usually linked
to a delivery date of the product. If the team exceeds the deadline, the team
failed in proper planning and / or effective execution of the plan. This can be the
result of: the wrong people on the wrong job (lack of communication between
teams, lack of experience, lack of commitment / drive / motivation, lack of
speed) or underestimation of the (complexity of the) requirements

Incremental SDLC Model
• Construct a partial
implementation of a total
system
• Then slowly add increased
functionality
• The incremental model
prioritizes requirements of the
system and then implements
them in groups.
• Each subsequent release of
the system adds function to the
previous release, until all
designed functionality has
been implemented.

Incremental Model Strengths
• Develop high-risk or major functions first
• Each release delivers an operational product
• Customer can respond to each build
• Uses “divide and conquer” breakdown of tasks
• Lowers initial delivery cost
• Initial product delivery is faster
• Customers get important functionality early
• Risk of changing requirements is reduced

Incremental Model
Weaknesses
• Requires good planning and design
• Requires early definition of a complete and fully
functional system to allow for the definition of
increments
• Well-defined module interfaces are required (some will
be developed long before others)
• Total cost of the complete system is not lower

When to use the Incremental
Model
• Most of the requirements are known up-front but are expected to
evolve over time
• A need to get basic functionality to the market early
• On projects which have lengthy development schedules
• On a project with new technology

Spiral SDLC Model
• Adds risk analysis,
and RAD prototyping
to the waterfall model
• Each cycle involves
the same sequence of
steps as the waterfall
process model

Spiral Quadrant
Determine objectives, alternatives and
constraints
• Objectives: functionality, performance,
hardware/software interface, critical success factors,
etc.
• Alternatives: build, reuse, buy, sub-contract, etc.
• Constraints: cost, schedule, interface, etc.

Spiral Quadrant
Evaluate alternatives, identify and
resolve risks
• Study alternatives relative to objectives and constraints
• Identify risks (lack of experience, new technology, tight
schedules, poor process, etc.
• Resolve risks (evaluate if money could be lost by
continuing system development

Spiral Quadrant
Develop next-level product
• Typical activities:
– Create a design
– Review design
– Develop code
– Inspect code
– Test product

Spiral Quadrant
Plan next phase
• Typical activities
– Develop project plan
– Develop configuration management plan
– Develop a test plan
– Develop an installation plan

Spiral Model Strengths
• Provides early indication of insurmountable risks, without much cost
• Users see the system early because of rapid prototyping tools
• Critical high-risk functions are developed first
• The design does not have to be perfect
• Users can be closely tied to all lifecycle steps
• Early and frequent feedback from users
• Cumulative costs assessed frequently

Spiral Model Weaknesses
• Time spent for evaluating risks too large for small or low-risk projects
• Time spent planning, resetting objectives, doing risk analysis and
prototyping may be excessive
• The model is complex
• Risk assessment expertise is required
• Spiral may continue indefinitely
• Developers must be reassigned during non-development phase activities
• May be hard to define objective, verifiable milestones that indicate
readiness to proceed through the next iteration

When to use Spiral Model
• When creation of a prototype is appropriate
• When costs and risk evaluation is important
• For medium to high-risk projects
• Long-term project commitment unwise because of potential changes to
economic priorities
• Users are unsure of their needs
• Requirements are complex
• New product line
• Significant changes are expected (research and exploration)

Agile SDLC’s
• Speed up or bypass one or more life cycle phases
• Usually less formal and reduced scope
• Used for time-critical applications
• Used in organizations that employ disciplined methods

Some Agile Methods
• Adaptive Software Development (ASD)
• Feature Driven Development (FDD)
• Crystal Clear
• Dynamic Software Development Method (DSDM)
• Rapid Application Development (RAD)
• Scrum
• Extreme Programming (XP)
• Rational Unify Process (RUP)

Dynamic Systems Development Method
(DSDM)
Applies a framework for RAD and short time frames
Paradigm is the 80/20 rule
– majority of the requirements can be delivered in a
relatively short amount of time.

DSDM Principles
1. Active user involvement imperative (Ambassador users)
2. DSDM teams empowered to make decisions
3. Focus on frequent product delivery
4. Product acceptance is fitness for business purpose
5. Iterative and incremental development - to converge on a solution
6. Requirements initially agreed at a high level
7. All changes made during development are reversible
8. Testing is integrated throughout the life cycle
9. Collaborative and co-operative approach among all stakeholders essential

DSDM Lifecycle
• Feasibility study
• Business study – prioritized requirements
• Functional model iteration
– risk analysis
– Time-box plan
• Design and build iteration
• Implementation

Adaptive Steps
1. Project initialization – determine intent of project
2. Determine the project time-box (estimation duration of the project)
3. Determine the optimal number of cycles and the time-box for each
4. Write an objective statement for each cycle
5. Assign primary components to each cycle
6. Develop a project task list
7. Review the success of a cycle
8. Plan the next cycle

Tailored SDLC Models
• Any one model does not fit all projects
• If there is nothing that fits a particular project, pick a model that
comes close and modify it for your needs.
• Project should consider risk but complete spiral too much – start
with spiral & pare it done
• Project delivered in increments but there are serious reliability
issues – combine incremental model with the V-shaped model
• Each team must pick or customize a SDLC model to fit its project

Readings & References
• Software Project Management by Bob Hughes &
Mike Cotterell (Chapter 4)

Lect-4: Software Development Life Cycle Model - SPM

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