Software Engineering CPCS351

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Software Engineering CPCS351

• Dr. Mai Fadel

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Software and Software Engineering

• The software engineers job is to solve problems
  economically by developing high-quality software.

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The Nature of Software

• Similarly to mechanical engineers who design
  mechanical systems, software engineers design
  software systems.
• Software differs from the types of artifacts
  produced by other types of engineers (how it
  affects s/w development)
• Software is largely intangible
• The mass-production of duplicate pieces of
  software is trivial
• The software industry is labour intensive
• It is all too easy for an inadequately trained
  software developer to create a piece of software
  that is difficult to understand and modify
• Software is physically easy to modify
• Software does not wear out with use

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Software Crisis

• Software crisis is the situation of software
  development in relationship with the expectation
  of the customers decades ago.
• Much of existing software is relatively poor
  quality, and is steadily becoming worse
• There is strong demand for new and changed
  software, which customers expect to be of high
  quality and to be produced rapidly
• The result of the poor development process
• Software engineers have not been able to live up
  to the expectations of their managers and
  customers
• Many software are either never delivered, or are
  delivered late and over budget
• Many software systems that are delivered are
  never put to use because they have so many
  problems
• Other systems require major modification before
  they can be used

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Software crisis- continued

• The challenges of developing software systems
• The complex nature of software
• The laws of economics (customer demands)
• The vagaries of human psychology
• In the authors opinion the situation is still
  going on
• Objective is to learn how to engineer software
  so that it meets expectations and doesnt
  contribute to the crisis

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Types of Software and their Differences

• Classification 1 of the types of software
• Custom software developed to meet the specific
  needs of a particular customer and tends to be of
  little use to others. e.g. web sites, air-traffic
  control systems
• Generic software/ (COTS)/ shrink-wrapped
  software is designed to be sold on the open
  market, to perform functions that many people
  need, and to run on general purpose computers.
  e.g. word processors, spreadsheets, web browsers,
  computer games.
• Embedded software run specific hardware devices
  which are typically sold on the open market. e.g.
  washing machines, DVD players, and automobiles
• It is possible to take generic software and
  customize it and vise versa.

condition in market Type of software
Highest number of copies in use Embedded S/W
Highest number of copies in use on general-purpose computers Generic S/W
What most developers work on Custom S/W
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Types of Software and their Differences -continue

• Classification 2 of the types of software
• Real-time software
• it has to react immediately (i.e. in real time)
  to stimuli from the environment (e.g. the pushing
  of a button, a signal from a sensor)
• Responsiveness must always be guaranteed- safety
  is a key concern in their design
• e.g. many of the embedded systems, custom systems
  that run industrial plants and telephone networks
• Data processing software
• is used to run businesses.
• It performs functions such as recording sales,
  managing accounts, printing bills etc.
• The design concern here is how to organize the
  data and provide useful information gathered to
  the users so they can perform their work
  effectively
• Accuracy and security of data are of major
  concern
• In traditional data processing tasks, data is
  gathered together in batches to be processed
  later.
• Some software has both real-time and data
  processing aspects.

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What is Software Engineering?

• Software Development and software engineering
• Definition software engineering is the process
  of solving customers problems by the systematic
  development and evolution of large, high-quality
  software systems within cost, time and other
  constraints
• Solving customers problems
• The goal of every software engineering project
• It is important to recognize activities that are
  not consistent with this goal, such as adding
  unnecessary features.
• Recognize situations when it would be most cost
  effective not to develop s/w at all, to develop
  simpler s/w or to purchase existing s/w.
• Software engineers must understand how people do
  their work, and understand what impact any
  proposed software may have on its users
  productivity (communicating negotiating with
  people)

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What is Software Engineering?-continue

• Systematic development and evolution
• Developing software by applying well-understood
  techniques in an organized and disciplined way.
• Software engineering is a young field
• There are many accepted practices that have been
  formally standardized by bodies such as IEEE, ISO
• Ensuring that the maintenance and evolution of
  existing systems is done in a systematic way is
  an integral part of software engineering
• Large, high-quality software systems
• Large systems with many functions and components
  , and thousands lines of code are too complex,
• difficult to understand, take too long to develop
  by one person, and challenging in dividing up the
  work among teams
• Software engineering techniques are essential for
  large system, and may be useful for small systems
• The end product must be of sufficient quality
  (there are techniques for improving quality and
  ensuring the product is of sufficient quality)

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What is Software Engineering?-continue

• Cost, time and other constraints
• One of the essential characteristics of
  engineering is that you have to consider economic
  constraints as you try to solve each problem
• There are 3 main economic constraints
• Software engineers must ensure their systems can
  be produced within a limited budget and by a
  certain due date
• Achieving this requires careful planning and
  sticking to the plan in a disciplined way, and
  creating a realistic plan in the first place
• Why many software engineering projects fail to
  stick to the specified time and cost constraints?

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Software Engineering as a Branch of the
Engineering Profession

• People have talked about software engineering
  since 1968 when the term was coined at a NATO
  conference
• Only since the mid-1990s has there been a shift
  towards recognizing software engineering as a
  distinct branch of the engineering profession
  (i.e. have a license to legally perform
  consulting or self-employed work)
• How to obtain a license? Licensing agencies
• Ensures sufficient engineering education
  experience
• Accredits educational institutions
• Licensed profession impose adherence to codes of
  ethics and taking responsibility for the produced
  work
• Universities have been establishing academic
  programs that focus on software engineering
  (distinct from computer science or computer
  engineering)

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Stakeholders in Software Engineering

• Stakeholders are the people involved in a
  software engineering project (who are they and
  what do they look for in interacting with the
  software? Figure 1.1 page12)
• Users people who will use the software. They
  will likely appreciate new software, but some may
  fear it would jeopardize their jobs
• Customers/clients people who make the decisions
  about ordering and paying for the software. They
  may or may not be users.
• Software Developers people who develop and
  maintain the software (such as software
  engineers). Special roles in a s/w engineering
  project include requirements specialists,
  database specialists, technical writers,
  configuration management specialists, etc.
• Development Managers people who run the
  organization that is developing the software,
  they usually have an educational background in
  business administration.
• In some cases, two, three or even all four of the
  stakeholders may be held by the same person

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Software Quality

• There is no single answer for the question what
  quality means? But the goal is to produce
  software with high quality
• Attributes of software quality (what is its
  impact on the software? How to measure it? what
  to do to improve it?)
• Software engineers try to balance the relative
  importance of these attributes towards the best
  overall quality
• Usability, efficiency, reliability,
  maintainability, and reusability
• The importance of these attributes varies from
  stakeholder to another and form system to system.
  (examples)
• Often, software engineers improve one quality at
  the expense of another trade-offs
• Good engineering practice sets objectives for
  quality that satisfies all stakeholders, and then
  designing the system to meet these objectives

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Software Engineering Projects

• S/w engineering work is normally divided into
  projects.
• For small s/w systems there may be a single team
  of three or four developers working on the
  project
• Evolutionary projects (those that involve
  modifying an existing system) corrective,
  adaptive, enhancement, re-engineering or
  perfective
• Greenfield projects (those that involve starting
  to develop a system from scratch)
• Projects that involve building on a framework or
  a set of existing components (those that involve
  building most of a new system from existing
  components, while developing new software only
  from missing details)

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Evolutionary Projects

• Most s/w projects are of this type- maintenance
• For many people, maintenance implies keeping
  something running by simply fixing problems, but
  without adding significant new features
• There is constant pressure from users and
  customers not only to fix problems but to make
  many other kinds of changes
• Radical modifications/ evolution should be
  applied after several years of frequent changes
  resulting in software that barely resembles their
  original state

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Types of Evolutionary Project

• Corrective projects involve fixing defects
• Adaptive projects involve changing the system in
  response to changes in the environment in which
  the software runs (a new version of Operating
  system, database, a new set of tax laws)
• Enhancement projects involves adding new features
• Re-engineering/ perfective projects involve
  changing the system internally so that it is more
  maintainable, without making significant changes
  that the user will notice
• Most evolutionary projects involve more than one
  of the above
• Legacy systems are software systems that require
  maintaining when a lot of the design information
  is missing

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Greenfield Projects

• Green projects are less common than evolutionary
• Developers have a wider freedom to be creative
  about the design no constraints of design
  decisions errors made by predecessors
• Take a lot of work to build

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Projects that involve reusing design/ code

• Starts with a framework or involves plugging
  together several components that are already
  developed and provide significant functionality
• A framework is a software system especially
  designed to be reused in different projects, or
  in various products in product line. A framework
  contains important functionality, but must be
  adapted to handle the requirements of particular
  customers or products
• e.g. framework for ticketing
• Basic functionality for reserving and printing
  tickets
• It can be used for theatres, cinema, sports
  events, a holiday package
• e.g. of the use of components (gluing an
  accounting package and a package for tracking
  meetingsgt a product for a lawyers office to
  create bills for clients meetings)
• Advantages
• Benefit from software that has been shown to be
  reliable, since the framework is tested
• Gives the freedom to innovate as with the case
  with Greenfield projects

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Activities Common to Software Projects

• Requirements and specification
• Design
• Modeling
• Programming
• Quality assurance
• Deployment
• Managing software configuration
• Managing the process

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Requirements and Specification

• It is important to, first, understand the
  problems, the customers business environment,
  and the available technology which can be used to
  solve the problems
• After that, meet with the customers and users to
  decide on a course of action that will solve the
  problems (development or modification)
• Then decide in detail what facilitates the
  software should provide
• Involved activities domain analysis, defining
  the problem, requirement gathering, requirement
  analysis, requirement specification (pp. 16-17)
• Important principle of requirement is to separate
  the what from the how i.e. requirements
  from design and implementation

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Design

• Design is the process of deciding how the
  requirements should be implemented using the
  available technology
• Some of the important activities during design
  system engineering, determining the software
  architecture, detailed designs, user interface
  design, etc.
• For large systems, software engineers work on
  architectural design in conjunction with
  high-level requirements to effectively divide the
  system into subsystems
• For small systems, requirement precede design to
  avoid re-doing the design if requirements change
  

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Modeling

• Modeling is the process of creating a
  representation of the domain or the software
• Various modeling approaches can be used during
  both requirements analysis and design.
• e.g. Use case, structural, and dynamic/
  behavioural modeling
• Modeling can be performed visually, using
  diagrams, or else using semi-formal or formal
  languages that express the information in a
  systematically or mathematically.
• e.g. UML with a semi-formal notation diagrams

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Programming

• It involves the translation of higher-level
  designs into particular programming languages
• The final stage of design since it involves
  making decisions about the appropriate
  constructs, variable declarations, etc.
• Programmers people who do higher-design
  activities and programming
• Coders perform only programming with no design
• Research is done on automating programming, e.g.
  code generators. However there will still be a
  need for manual programming

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Quality Assurance (QA)

• QA encompasses all the processes needed to ensure
  that the quality objectives discussed in Section
  1.5 are met
• Occurs throughout the project
• Involved activities reviews and inspection, and
  testing
• Validation and Verification (V V)
• Validation the process of determining whether
  the requirements will solve the customers
  problem
• Verification the process of making sure the
  requirements have been adhered to

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Other activities

• Deployment involves distributing and installing
  the software and any other components of the
  system such as databases, special hardware, etc.
• Managing software configurations involves
  identifying all the components that compose a
  software system, including files containing
  requirements, design, and source code.
• Managing the Process managers lead the other
  activities, and undertake the following task
• Estimating the cost of the system
• Planning
• Periodically Revising the expected estimates and
  planning