An Introduction to Software Engineering by Prof. Mark Ramsey

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An Introduction to Software Engineeringby Prof.
Mark Ramsey

• Introductions
• Introduction to Software Engineering
• Software Specification
• Software Design
• Software Validation
• Software Management

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An Introduction to Software EngineeringIntroducti
on

• How Did We Get Here?
• Well-Engineered Software
• The Software Process
• Management Process Models

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An Introduction to Software EngineeringHow Did
We Get Here?

• Computer Hardware is decreasing while computer
  systems are being incorporated in more more
  products.
• Boehm states that in 1985 software costs 140
  Billion
• Growing at a rate of 12 per year - 763 Billion
  in 2000
• What is Software Engineering
• Software Systems built by teams rather than
  individuals.
• Includes Engineering Principles in development of
  these systems.
• Technical as well as Non-Technical Aspects

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An Introduction to Software EngineeringHow Did
We Get Here?

• Term Software Engineering first introduced in
  the late 1960s at a conference.
• Industry was trying to address the software
  crisis as a result of the introduction of 3rd
  Generation computer hardware.
• This new hardware made large software systems
  possible(needed).
• New techniques were needed to control the
  complexity inherent in large software systems
• Industry well ahead of Academia
• Computer Science vs Mathematics
• Information Systems vs Computer Science
• Software Engineering vs Computer Engineering

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An Introduction to Software Engineering
Well-Engineered Software

• Like all engineering, Software Engineering is not
  just about producing products, but producing
  products is a cost-effective way.
• Four key attributes which a well-engineered
  software system should possess
• Should be maintainable
• Should be reliable
• Should be efficient
• Should offer an appropriate User interface

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An Introduction to Software Engineering The
Software Process

• In 1970 the notion that software development is
  like other engineering processes resulted in
  Royce developing a model for Software
  Development. The first being the Waterfall Model
  (Software Life Cycle)

Requirements analyst and definition
System and Software Design
Implementation and Unit Testing
Integration and System Testing
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An Introduction to Software Engineering The
Software Process

• Detailed software process models are still the
  subject of research. But there are a number of
  different models or paradigms of software
  development
• The Waterfall Approach number of stages
• Exploratory Programming develop a working system
  as quickly as possible and modify as needed
• Prototyping Establish system requirements
• Formal transformation developing a formal
  specification of the software system and
  transforming into a program
• System assembly from reusable components
  assembling already existing software components
• The first 3 are used currently for all practical
  systems development

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An Introduction to Software Engineering The
Software Process

• Software Development Life Cycle
• Requirements Analysis and Definitions
• System and Software Design
• Implementation and Unit Testing
• Integration and System Testing
• Operations and Maintenance

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An Introduction to Software Engineering The
Software Process

• An aim of software engineering is to reduce
  overall software costs so the cost distribution
  across the software process must be known.
• System Type Req/Design Impl Testing
• Control Systems 46 20
  34
• Spaceborne Systems 34 20
  46
• Operating Systems 33 17 50
• Scientific Systems 44 26 30
• Business Systems 44 28 28

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An Introduction to Software Engineering
Management Process Models

• Project Management is one thing which
  distinguishes professional software engineering
  and no process model can be acceptable if it
  results in an unmanageable process.
• Activity Output documents
• Requirements Analysis Feasibility Study/ Outline
  Requirements
• Requirements Definition Requirements
  Specification
• System Specification Functional Specs/Acceptance
  Test Specs/Draft User Manual
• Architectural Design Design Architecture
  Specs/System Test Specs
• Interface Design Interface Specs/Integration
  Test Specs
• Detailed Design Design Specs/Unit Test Specs
• Coding Program Code
• Unit Testing Unit Test Result Report
• Module Testing Module Test Result Report
• Integration Testing Integration Test
  Report/Final User Manual
• System Testing System Test Report
• Acceptance Testing Final System

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An Introduction to Software Engineering Review
Point

• Software engineering involves technical
  non-technical issues. As well as knowledge of
  specification, design, and implementation
  techniques, software engineers must know
  something about human factors and software
  management.
• Well-Engineered software is software which
  provides the services required by its users. It
  should be maintained, reliable and efficient, and
  should provide an appropriate user interface.
• The waterfall model of software development
  suffers from inadequacies but will continue to be
  widely used because it simplifies management of
  the software process.
• Exploratory programming is not suited to the
  development of most large, long-lifetime software
  systems because it is likely to result in systems
  which are expensive to maintain.
• Document-driven management process models suffer
  from the disadvantage that they inhibit process
  iteration because documents are frozen and then
  become very expensive to change.

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An Introduction to Software Engineering Exercise
1

• A university intends to procure an integrated
  student management system holding all details of
  registered students including personal
  information, courses taken, and examination marks
  achieved. The alternative approaches to be
  adopted are
• Buy a database management system and develop an
  in-house system based on this database.
• Buy a comparable system from another university
  and modify it to local requirements
• Join a consortium of other universities,
  establish a common set of requirements and
  contract a software house to develop a single
  system for all the universities in the
  consortium
• Identify two possible risks in each of these
  strategies and suggest techniques for risk
  resolution which would help in deciding which
  approach to adopt.

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An Introduction to Software Engineering Exercise
2

• Write a plausible requirements definition for the
  following functions
• An unattended petrol (gas) pump system which
  includes a credit card reader. The customer
  swipes the card through the reader then specifies
  the amount of fuel required. The fuel is
  delivered and the customers account is debited.
• The cash dispensing function in a bank
  auto-teller machine.
• The spell checking and correcting function in a
  word processor.

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An Introduction to Software Engineering Software
Design

• Design is a creative process. Although methods
  guidelines are helpful, judgement flair on the
  part of the software engineer are still required
  to design a software system.
• The main design activities in the software
  process are architectural design, system
  specification, interface design, component
  design, data structure design and algorithm
  design.
• Functional decomposition involves considering a
  system as a set of interacting functional units.
• Object-oriented decomposition considers the
  system as a set of objects where an object is an
  entity with state and functions to inspect and
  modify that state.
• A decision on whether a system should be
  implemented as a single sequential process or as
  a number of parallel processes is a detailed
  design decision. The design process should
  partition the system into logical, interacting
  units which may be realized as either sequential
  or parallel components.
• The most important design quality attribute is
  maintainability. Maximizing cohesion in a
  component minimizing the coupling between
  components is likely to lead to maintainable
  design.
• The use of inheritance in object-oriented systems
  can improve the quality of a design but may make
  the design more difficult to understand.

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An Introduction to Software Engineering Exercise
3

• Explain why sequential software designs are
  easier to validate than designs which involve
  parallel processes

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An Introduction to Software Engineering
Verification Validation

• Verification Validation are not the same thing.
  Verification is intended to show that a program
  meets its specification. Validation is intended
  to show that the program does what the user wants
  it to do.
• Testing has a dual function it is used to
  establish the presence of defects in a program
  and it is used to estimate whether or not the
  program is operationally usable.
• Testing can only be demonstrated the presence of
  errors. It cannot prove their absence.
• The testing process involves unit testing, module
  testing, sub-system testing, integration testing
  and acceptance testing.
• Testing should be scheduled as part of the
  project planning process. Adequate resources must
  be made available for testing.
• Testing strategies which may be adopted include
  top-down testing, bottom-up testing, thread
  testing of real-time systems and stress testing.

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An Introduction to Software Engineering Exercise
4

• Describe four classes of systems encountered in
  everyday life which might be subject to stress
  testing.

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An Introduction to Software Engineering Software
Management

• Good software project management is essential if
  software engineering projects are to be developed
  on schedule and within budget.
• Software management is different from other
  engineering management because software is
  intangible, because we dont understand the
  software process and because many projects are
  novel and innovative.
• A software manager has diverse roles but the most
  significant activities are project planning,
  estimating, and scheduling.
• Various development team organizations have been
  adopted. Democratic teams work well with
  experienced and competent staff. Chief programmer
  teams try to make best use a scarce resource,
  namely, programming skills.
• The dominant factor in programming productivity
  is the aptitude of the individual programmer.
• Existing measures of programming productivity do
  not take the quality of the finished product into
  account.

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An Introduction to Software Engineering Exercise
5

• Explain why the productivity of programmers
  working on embedded systems is usually very much
  lower than that of programmers developing
  business information systems.