COSC 4406 Software Engineering

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COSC 4406Software Engineering
Haibin Zhu, Ph.D. Dept. of Computer Science and
mathematics, Nipissing University, 100 College
Dr., North Bay, ON P1B 8L7, Canada,
haibinz_at_nipissingu.ca, http//www.nipissingu.ca/fa
culty/haibinz
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Lecture 2Process Models and Agile Development
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Prescriptive Models

• They define a distinct set of activities,
  actions, tasks, milestones, and work products
  that are required to engineering high-quality
  software. They are not perfect, but they do
  provide a useful roadmap for software engineering
  work.

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Prescriptive Models

• Prescriptive process models advocate an orderly
  approach to software engineering
• That leads to a few questions
• If prescriptive process models strive for
  structure and order, are they inappropriate for a
  software world that thrives on change?
• Yet, if we reject traditional process models (and
  the order they imply) and replace them with
  something less structured, do we make it
  impossible to achieve coordination and coherence
  in software work?

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The Waterfall Model
http//www.stsc.hill.af.mil/crosstalk/1995/01/Comp
aris.asp
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The Incremental Model
Communication Planning Modeling (analysis,
design) Construction Deployment (deliver,
feedback)
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The RAD Model
It is an incremental model that emphasizes a
short development cycle by using component-based
approach.
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Evolutionary Models Prototyping
Quick plan
communication
Modeling Quick design
Deployment delivery feedback
Construction of prototype
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Strengths and Weaknesses of Prototyping

• Strengths of Prototyping
• Early functionality.
• Provides a process to perfect the requirements
  definition.
• Provides risk control.
• Documentation focuses on the end product not the
  evolution of the product.
• Provides a formal specification embodied in an
  operating replica.
• Weaknesses of Prototyping
• Less applicable to existing systems than to new,
  original development.
• Bad reputation among conservatives as a "quick
  and dirty" method.
• Suffers from bad documentation.
• Sometimes produces a system with poor
  performance.
• Tendency for difficult problems to be pushed to
  the future so that the initial promise of the
  prototype is not met by subsequent products.

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Comparing the incremental model and the
prototyping model

• Same
• They are iterative
• Difference
• The former focuses on the delivery of an
  operational product with each increment.
• The latter focuses on a representation of those
  aspects of the software that will be visible to
  the customer/end-user.

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Evolutionary Models The Spiral
It couples the iterative nature of prototyping
with the controlled and systematic aspects of
the waterfall model.
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STRENGTHS Water-fall Incremental Spiral
Allows for work force specialization X X X
Orderliness appeals to management X X X
Can be reported about X X X
Facilitates allocation of resources X X X
Early functionality X X
Does not require a complete set of requirements at the onset X X
Resources can be held constant X
Control costs and risk through prototyping X
The incremental model may be used with a complete set of requirements or with less defined general objectives.
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WEAKNESSES Waterfall Incremental Spiral
Requires a complete set of requirements at the onset X
Enforcement of non-implementation attitude hampers analyst/designer communications X
Beginning with less defined general objectives may be uncomfortable for management X X
Requires clean interfaces between modules X
Incompatibility with a formal review and audit procedure X X
Tendency for difficult problems to be pushed to the future so that the initial promise of the first increment is not met by subsequent products X X
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Evolutionary Models Concurrent
For each framework activity of the waterfall
model, there is a state transition diagram. Each
activity follows the diagram. Therefore, all
these activities are in concurrency.
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Still Other Process Models

• Component based developmentthe process to apply
  when reuse is a development objective
• Formal methodsemphasizes the mathematical
  specification of requirements
• AOSDprovides a process and methodological
  approach for defining, specifying, designing, and
  constructing aspects
• Unified Processa use-case driven,
  architecture-centric, iterative and incremental
  software process closely aligned with the Unified
  Modeling Language (UML)

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The Unified Process (UP)
inception
elaboration
Introduce agile features into The activities of
the waterfall model. Iterative, incremental.
inception
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UP Phases
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UP Work Products
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Agile Software Engineering

• It combines a philosophy and a set of development
  guidelines.
• The philosophy encourages
• customer satisfaction and early incremental
  delivery of software
• small, highly motivated project teams
• informal methods
• minimal software engineering products and
• overall development simplicity.
• The development guidelines stress delivery over
  analysis and design and active and continuous
  communication between developers and customers.

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The Manifesto for Agile Software Development

• We are uncovering better ways of developing
  software by doing it and helping others do it.
  Through this work we have come to value
• Individuals and interactions / processes and
  tools
• Working software / comprehensive documentation
• Customer collaboration / contract negotiation
• Responding to change / following a plan
• That is, while there is value in the items on the
  right, we value the items on the left more.

Kent Beck et al
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Human Factors

• Competence
• Common Focus
• Collaboration
• Decision-making ability
• Fuzzy problem-solving ability
• Mutual trust and respect
• Self-organization

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What is Agility?

• Effective (rapid and adaptive) response to change
• Effective communication among all stakeholders
• Drawing the customer onto the team
• Organizing a team so that it is in control of the
  work performed
• Yielding
• Rapid, incremental delivery of software

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An Agile Process

• Is driven by customer descriptions of what is
  required (scenarios)
• Recognizes that plans are short-lived
• Develops software iteratively with a heavy
  emphasis on construction activities
• Delivers multiple software increments
• Adapts as changes occur

• Assumptions
• It is difficult to predict in advance the
  requirements
• Phases are interleaved.
• All the phases are not predictable.

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Extreme Programming (XP)

• The most widely used agile process, originally
  proposed by Kent Beck
• XP Planning
• Begins with the creation of user stories
• Agile team assesses each story and assigns a cost
• Stories are grouped for a deliverable increment
• A commitment is made on delivery date
• After the first increment project velocity is
  used to help define subsequent delivery dates for
  other increments

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Extreme Programming (XP)

• XP Design
• Follows the KIS principle
• Encourage the use of CRC cards (see Chapter 8)
• For difficult design problems, suggests the
  creation of spike solutionsa design prototype
• Encourages refactoringan iterative refinement
  of the internal program design
• XP Coding
• Recommends the construction of a unit test for a
  store before coding commences
• Encourages pair programming
• XP Testing
• All unit tests are executed daily
• Acceptance tests are defined by the customer
  and excuted to assess customer visible
  functionality

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Extreme Programming (XP)
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Adaptive Software Development

• Originally proposed by Jim Highsmith
• ASD distinguishing features
  Self-oraganisation
• Mission-driven planning
• Component-based focus
• Uses time-boxing (See Chapter 24)
• Explicit consideration of risks
• Emphasizes collaboration for requirements
  gathering
• Emphasizes learning throughout the process

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Adaptive Software Development
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Dynamic Systems Development Method

• Promoted by the DSDM Consortium (www.dsdm.org)
• Provides a framework for building systems that
  meet tight time constraints through the use of
  incremental prototyping in a controlled project
  environment.
• DSDMdistinguishing features
• Similar in most respects to XP and/or ASD
• Nine guiding principles
• Active user involvement is imperative.
• DSDM teams must be empowered to make decisions.
• The focus is on frequent delivery of products.
• Fitness for business purpose is the essential
  criterion for acceptance of deliverables.
• Iterative and incremental development is
  necessary to converge on an accurate business
  solution.
• All changes during development are reversible.
• Requirements are baselined at a high level
• Testing is integrated throughout the life-cycle.

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Dynamic Systems Development Method
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Scrum

• Originally proposed by Schwaber and Beedle
• Scrumdistinguishing features
• Development work is partitioned into packets
• Testing and documentation are on-going as the
  product is constructed
• Work occurs in sprints and is derived from a
  backlog of existing requirements
• Meetings are very short and sometimes conducted
  without chairs
• demos are delivered to the customer with the
  time-box allocated

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Scrum
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Crystal

• Proposed by Cockburn and Highsmith
• Crystaldistinguishing features
• Actually a family of process models that allow
  maneuverability based on problem
  characteristics
• Face-to-face communication is emphasized
• Suggests the use of reflection workshops to
  review the work habits of the team

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Feature Driven Development

• Originally proposed by Peter Coad et al
• FDDdistinguishing features
• Emphasis is on defining features
• a feature is a client-valued function that can
  be implemented in two weeks or less.
• Uses a feature template
• ltactiongt the ltresultgt ltby for of togt a(n)
  ltobjectgt
• A features list is created and plan by feature
  is conducted
• Design and construction merge in FDD

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Feature Driven Development
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Agile Modeling

• Originally proposed by Scott Ambler
• Suggests a set of agile modeling principles
• Model with a purpose
• Use multiple models
• Travel light
• Content is more important than representation
• Know the models and the tools you use to create
  them
• Adapt locally

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Summary

• Prescriptive Models
• The Waterfall Model
• The Incremental Model
• The RAD Model
• Evolutionary Models
• Prototyping
• The Spiral Model
• The Current Development Model
• UP Phase
• Agile Development
• Agile processes
• Agile process models
• XP, ASD, DSDM, Scum, Crystal, FDD, AM