SE_Lec 01_ Introduction to Software Enginerring

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 Introduction to Software
 Introduction to Software Engineering
 Software Components
 Software Process
 Classification of Programming Techniques

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 Definition of Software:
 Software includes
• Computer programs (Instructions) that when executed
provide desired functions and performance.
• Data structures that enable the programs to adequately
manipulate information.
• Documents that describe the operation and use of the
programs.
 Software is ~10x more expensive to produce than a
computer program [Brooks75]

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 Computer software has become a driving force.
 It is the engine that drives business decision making.
 It serves as the basis for modern scientific investigation
and engineering problem-solving.
 It is embedded in all kinds of systems, such as
transportation, medical, telecommunications, military,
industrial processes, entertainment, office products, etc.

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 Computer software is often divided into two categories:

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 Software is classified into the following two classes:
 Generic Software.
• Stand-alone systems that are marketed and sold to any
customer who wishes to buy them.
• Examples – PC software such as graphics programs, project
management tools; CAD software; software for specific
markets such as appointments systems for dentists.
 Customized Software.
• Software that is commissioned by a specific customer to
meet their own needs.
• Examples – embedded control systems, air traffic control
software, traffic monitoring systems.

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 Software Engineering is a discipline whose aim is the
production of fault free software that satisfies the
user’s needs and that is delivered on time and within
budget
 Software Engineering is a collection of techniques,
methodologies and tools that help with the production
of A high quality software system developed with a
given budget before a given deadline while change
occurs

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 The software crisis has been with us since the 1970s. As
per the latest IBM report,
 “31% of the projects get cancelled before they are
completed,
 53% over-run their cost-estimates by an average of 189% ,
 and for every 100 projects, there are 94 restarts.”

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 Size: large
 User is not the developer
 Lifespan: long (no ageing)
 Cost: development + operation/maintenance

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 Kitchen table: 5-10 components
 Bicycle: 20-100 components
 Car: 30.000 parts/components
 Airplane: 100.000 parts/components.
 Cell phone Software, printer driver Software : 1M Lines
of code
 Cellular network Software, operating system: several
Millions

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 Windows 7 about 50 millions lines of code.
 http://answers.yahoo.com/question/index?qid=200807121
32328AAwyert
 An Android operating system in a smart phone consists
of 12 million lines of code.
 https://docs.google.com/viewer?url=https%3A%2F%2Fptop.only.wip.la%3A443%2Fhttp%2Fwww.
rttonline.co
 Boeing’s new 787 Dreamliner requires about 6.5 million
lines of software code to operate its avionics and
onboard support systems.
 http://spectrum.ieee.org/green-tech/advanced-cars/this-
car-runs-on-co

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 Software engineering helps to reduce the programming
complexity.
 software products have to easy to
 Alter  Debug  Enhance
 Use resources optimally  Meet the user requirements.
 Software engineering principles use two important techniques
to deal with Complexity (reduce problem complexity):
 Abstraction.
 Decomposition
Increase in development time
and effort with problem size

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Decomposition of a large problem into a set of smaller
problems

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 Programs
 are developed by individuals for their personal use
 are Small in size
 have limited functionality
 the programmer himself is the sole user
 a single developer is involved
 the user interface may not be very important
 very little documentation is expected
 can be developed according to the programmer’s
individual style of development

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 Software is described by
 Its capabilities
• Functions it executes.
• Features it provides.
• Facilities it offers.
 The platform specifications that are required to run it.
• Certain hardware
• Certain operating system

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 Maintainability: software should be written in such a
way that it may evolve to meet the changing needs of
customer.
 Dependability: software dependability has a range of
characteristics, including reliability, security and
safety.
 Efficiency: efficiency includes responsiveness,
processing time, memory utilization etc…
 Usability: it should have an appropriate user interface
and adequate documentation.

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 Software is free
 a medium sized project with 50.000 LOC costs between
$400.000 to $1.600.000 in personnel
 Software is soft
 Changing it is difficult and costly than hardware.
 Cost of maintenance > cost of development.
 Maintenance becomes impossible at a certain point
 Software is produced
 Software is not mass produced (like machines)
 Software is developed
 Software ages
 Failures do not occur due to material fatigue (as with hardware)
but due to the execution of logical faults
 Software changes due to requirements changes, platform
changes.

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 Programming skill not enough
 Software engineering involves "programming-in the–
large"
 understand requirements and write specifications
• derive models and reason about them
 master software
 operate at various abstraction levels
 member of a team
• communication skills
• management skills

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 The job of software engineers is to
 produce quality products
 produce them on schedule
 and do this work for the planned costs
 In this class I hope we will learn some of this
 You will also need a lot of practice!!

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 Software costs often dominate computer system costs.
The costs of software on a PC are often greater than the
hardware cost.
 Software costs more to maintain than it does to
develop. For systems with a long life, maintenance costs
may be several times development costs.

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 A software component is a system element offering a
predefined service and is able to communicate with
other components.
 The Software component shall be
 Multiple-use
 Non-context-specific
 Composable with other components
 Encapsulated, i.e., non-investigable through its interfaces
 A unit of independent deployment and versioning

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 The component needs
 to be fully documented.
 to be more thoroughly tested.
 to have robust input validity checking.
 to pass back useful error messages as appropriate.
 to be built with an awareness that it will be put to
unforeseen uses.
 a mechanism for compensating developers who invest the
(substantial) effort implied above.

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 For success in large software development, It is
important to follow an Engineering approach, consisting
of a well-defined process.
 A process: is a series of steps involving activities,
constraints, and resources that produce an intended
output of some kind.
 A process involves a set of tools and techniques.
 A software process: is the related set of activities and
processes that are involved in developing and evolving a
software system.
 A Software process: deals with both technical and
management issues.

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 Process: activities, people, tools
 Products: documents, data, code.
 The quality of the product depends on the quality of the
process
Process
Product

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 Software specifications: The functionality of the
software and constraints on its operation must be
defined.
 Software development: Software that meets the
specifications must be produced.
 Software validation: The software must be validated to
ensure that it does what the customer wants.
 Software evolution: The software must evolve to meet
changing customer needs.

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 Unstructured programming. [use of GOTO ]
 Procedural programming.
 Modular programming.
 Object-oriented programming.

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 Structured programs are easier to
 easier to read and understand.
 easier to maintain.
 require less effort and time for development.
 easier debugging and usually fewer errors are made in the
course of writing such programs.

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 Assembly language.
 High-level language programming. (FORTRAN, ALGOL,
and COBOL )
 Control flow structure design, and the use of "GOTO"
statement  Jump.
 Control flow structure design, and the use of (selection,
sequence and iteration)
 Data structure-oriented design.
 Data flow-oriented design technique.
 Object-oriented design.

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 Exploratory software development style is based on
error correction
 developing a working system as quickly as possible and
then successively modifying it until it performed
satisfactorily.
 The software engineering principles are primarily based
on error prevention

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 A personal insulin pump
 An embedded system in an insulin pump used by diabetics
to maintain blood glucose control.
 A mental health case patient management system
 A system used to maintain records of people receiving care
for mental health problems.

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 Collects data from a blood sugar sensor and calculates
the amount of insulin required to be injected.
 Calculation based on the rate of change of blood sugar
levels.
 Sends signals to a micro-pump to deliver the correct
dose of insulin.
 Safety-critical system as low blood sugars can lead to
brain malfunctioning, coma and death; high-blood sugar
levels have long-term consequences such as eye and
kidney damage.

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Figure 1.4: Insulin pump hardware

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Figure 1.5: Activity model of the insulin pump

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 The system shall be available to deliver insulin when
required.
 The system shall perform reliably and deliver the
correct amount of insulin to counteract the current level
of blood sugar.
 The system must therefore be designed and
implemented to ensure that the system always meets
these requirements.

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 A patient information system to support mental health
care is a medical information system that maintains
information about patients suffering from mental health
problems and the treatments that they have received.
 Most mental health patients do not require dedicated
hospital treatment but need to attend specialist clinics
regularly where they can meet a doctor who has
detailed knowledge of their problems.
 To make it easier for patients to attend, these clinics
are not just run in hospitals. They may also be held in
local medical practices or community centres.

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 The MHC-PMS (Mental Health Care-Patient Management
System) is an information system that is intended for use
in clinics.
 It makes use of a centralized database of patient
information but has also been designed to run on a PC,
so that it may be accessed and used from sites that do
not have secure network connectivity.
 When the local systems have secure network access,
they use patient information in the database but they
can download and use local copies of patient records
when they are disconnected.

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 To generate management information that allows health
service managers to assess performance against local
and government targets.
 To provide medical staff with timely information to
support the treatment of patients.

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Figure 1.6: The organization of the MHC-PMS

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 Individual care management
 Clinicians can create records for patients, edit the
information in the system, view patient history, etc. The
system supports data summaries so that doctors can
quickly learn about the key problems and treatments that
have been prescribed.
 Patient monitoring
 The system monitors the records of patients that are
involved in treatment and issues warnings if possible
problems are detected.
 Administrative reporting
 The system generates monthly management reports
showing the number of patients treated at each clinic, the
number of patients who have entered and left the care
system, number of patients sectioned, the drugs
prescribed and their costs, etc.

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 Privacy
 It is essential that patient information is confidential and
is never disclosed to anyone apart from authorised medical
staff and the patient themselves.
 Safety
 Some mental illnesses cause patients to become suicidal or
a danger to other people. Wherever possible, the system
should warn medical staff about potentially suicidal or
dangerous patients.
 The system must be available when needed otherwise
safety may be compromised and it may be impossible to
prescribe the correct medication to patients.

SE_Lec 01_ Introduction to Software Enginerring

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SE_Lec 01_ Introduction to Software Enginerring