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Software Engineering

Lecture1 - Introduction

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Contact Information

• Website: CS450.wikispaces.com

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Required Textbook

• “ Software Engineering”, by Ian Sommerville, The international Computer Science Series, The Latest Edition (9 th).

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Grading

Mid Term 1 Week 7 20 %

Mid Term2 Week 12 20 %

Assignments Week 5, 10 10 %

Final Exam After Week 15 50 %

Total 100 %

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Lecture Format

• Help you understand important and hard Media and Multimedia Systems concepts

• Lectures do not cover everything

• Students responsibility:o Attend lectureso Read textbooks o Download lectureso Assignments, Exams

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Course Content

• Introduction to software engineering.• Software processes and software process models.• Distinct between software validation and software verification.• Principal requirements of engineering activities.• Concepts of system modeling.• Decisions about the system architecture during the architectural design process.• Use and apply Unified Modeling Language (UML).

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Topics Covered

• Professional software development– What is meant by software engineering.

• Software engineering ethics– A brief introduction to ethical issues that affect software

engineering.

• Case studies– An introduction to three examples that are used in later

chapters in the book.

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Professional Software Development

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Why Software Engineering?

• The economies of ALL developed nations are dependent on software.

• More and more systems are software controlled.

•Software development is hard.

•Important to distinguish between:• “Easy” systems (one developer, one user, experimental use

only) and • “Hard” systems (multiple developers, multiple users,

products)

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Software Costs

• 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.

• Software engineering is concerned with cost-effective software development.

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Software Products

• Generic products– 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;

• Customized products– 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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Product specification

• Generic products– The specification of what the software should do is owned

by the software developer and decisions on software change are made by the developer.

• Customized products– The specification of what the software should do is owned

by the customer for the software and they make decisions on software changes that are required.

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FAQs about software engineering

• What is software?• What is software engineering?• What is the difference between software engineering

and computer science?• What is the difference between software engineering

and system engineering?• What is a software process?• What is a software process model?

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FAQs about software engineering

• What are the costs of software engineering?• What are software engineering methods?• What is CASE (Computer-Aided Software

Engineering)• What are the attributes of good software?• What are the key challenges facing software

engineering?

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What is software?

• Computer programs and associated documentation such as requirements, design models and user manuals.

• Software products may be developed for a particular customer or may be for a general market.

• Software products may be– Generic - developed to be sold to a range of different

customers (e.g. PC software such as Excel or Word).– Bespoke (custom) - developed for a single customer

according to their specification.• New software can be created by developing new programs,

configuring generic software systems or reusing existing software.

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What is software engineering?

• Software engineering is an engineering discipline that is concerned with all aspects of software production.

• Software engineers should adopt a systematic and organised approach to their work and use appropriate tools and techniques depending on the problem to be solved, the development constraints and the resources available.

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What is the difference between software engineering and computer science?

• Computer science is concerned with theory and fundamentals;

• Software engineering is concerned with the practicalities of developing and delivering useful software.

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What is the difference between software engineering and system engineering?

• System engineering is concerned with all aspects of computer-based systems development including (hardware, software and process engineering).

• Software engineering is part of this process concerned with (developing the software infrastructure, control applications and databases) in the system.

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What is a software process?

• A set of activities whose goal is the development or evolution of software.

• Generic activities in all software processes are:– Specification - what the system should do and its

constraints– Development - production of the software system– Validation - checking that the software is what the

customer wants– Evolution - changing the software in response to

changing demands.

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What is a software process model?

• A simplified representation of a software process, presented from a specific perspective.

• Examples of process perspectives are– Workflow perspective - sequence of activities;– Data-flow perspective - information flow;– Role/action perspective - who does what.

• Generic process models– Waterfall;– Iterative development;– Component-based software engineering.

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What are the costs of software engineering?

• Roughly 60% of costs are development costs, 40% are testing costs. For custom software, evolution costs often exceed development costs.

• Costs vary depending on the type of system being developed and the requirements of system attributes such as performance and system reliability.

• Distribution of costs depends on the development model that is used.

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What are software engineering methods?

• Structured approaches to software development which include system models, notations, rules, design advice and process guidance.

• Model descriptions– Descriptions of graphical models which should be produced;

• Rules– Constraints applied to system models;

• Recommendations– Advice on good design practice;

• Process guidance– What activities to follow.

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What is CASE (Computer-Aided Software Engineering)

• Software systems that are intended to provide automated support for software process activities.

• Upper-CASE– Tools to support the early process activities of

requirements and design;• Lower-CASE

– Tools to support later activities such as programming, debugging and testing.

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What are the attributes of good software?

The software should deliver the required functionality and

performance to the user and should be maintainable, dependable

and acceptable.

• Maintainability– Software must evolve to meet changing needs;

• Dependability– Software must be trustworthy;

• Efficiency– Software should not make wasteful use of system resources;

• Acceptability– Software must be acceptable to the type of users for which it is designed.

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What are the key challenges facing software engineering?

• Heterogeneity– Developing techniques for building software that can cope

with heterogeneous platforms and execution environments;

• Delivery– Developing techniques that lead to faster delivery of

software;

• Trust– Developing techniques that demonstrate that software can be

trusted by its users.

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Software Engineering Diversity

• There are many different types of software system and there is no universal set of software techniques that is applicable to all of these.

• The software engineering methods and tools used depend on the type of application being developed, the requirements of the customer and the background of the development team.

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Application Types

• Stand-alone applications

– These are application systems that run on a local computer, such as a PC. They include all necessary functionality and do not need to be connected to a network.

• Interactive transaction-based applications

– Applications that execute on a remote computer and are accessed by users from their own PCs or terminals. These include web applications such as E-commerce applications.

• Embedded control systems

– These are software control systems that control and manage hardware devices.

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Application Types

• Batch processing systems– These are business systems that are designed to process data

in large batches. They process large numbers of individual inputs to create corresponding outputs.

• Entertainment systems– These are systems that are primarily for personal use and

which are intended to entertain the user.

• Systems for modelling and simulation– These are systems that are developed by scientists and

engineers to model physical processes or situations, which include many, separate, interacting objects.

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Application Types

• Data collection systems– These are systems that collect data from their

environment using a set of sensors and send that data to other systems for processing.

• Systems of systems– These are systems that are composed of a number

of other software systems.

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Software engineering fundamentals

• Some fundamental principles apply to all types of software system, irrespective of the development techniques used:

– Systems should be developed using a managed and understood development process.

– Dependability and performance are important for all types of system.

– Understanding and managing the software specification and requirements (what the software should do) are important.

– Where appropriate, you should reuse software that has already been developed rather than write new software.

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Software Engineering Ethics

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Professional and ethical responsibility

• Software engineering involves wider responsibilities than simply the application of technical skills.

• Software engineers must behave in an honest and ethically responsible way if they are to be respected as professionals.

• Ethical behaviour is more than simply upholding the law but involves following a set of principles that are morally correct.

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• Confidentiality – Engineers should normally respect the

confidentiality of their employers or clients irrespective of whether or not a formal confidentiality agreement has been signed.

• Competence – Engineers should not misrepresent their level of

competence. They should not knowingly accept work which is out with their competence.

Professional and ethical responsibility

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• Intellectual property rights – Engineers should be aware of local laws governing the use

of intellectual property such as patents, copyright, etc. They should be careful to ensure that the intellectual property of employers and clients is protected.

• Computer misuse – Software engineers should not use their technical skills to

misuse other people’s computers. Computer misuse ranges from relatively trivial (game playing on an employer’s machine) to extremely serious (dissemination of viruses).

Professional and ethical responsibility

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ACM/IEEE Code of Ethics

• The professional societies in the US have cooperated to produce a code of ethical practice.

• Members of these organisations sign up to the code of practice when they join.

• The Code contains eight Principles related to the behaviour of and decisions made by professional software engineers, including practitioners, educators, managers, supervisors and policy makers, as well as trainees and students of the profession.

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Ethical principles

1. PUBLIC - Software engineers shall act consistently with the public interest.

2. CLIENT AND EMPLOYER - Software engineers shall act in a manner that is in the best interests of their client and employer consistent with the public interest.

3. PRODUCT - Software engineers shall ensure that their products and related modifications meet the highest professional standards possible.

4. JUDGMENT - Software engineers shall maintain integrity and independence in their professional judgment.

5. MANAGEMENT - Software engineering managers and leaders shall subscribe to and promote an ethical approach to the management of software development and maintenance.

6. PROFESSION - Software engineers shall advance the integrity and reputation of the profession consistent with the public interest.

7. COLLEAGUES - Software engineers shall be fair to and supportive of their colleagues.

8. SELF - Software engineers shall participate in lifelong learning regarding the practice of their profession and shall promote an ethical approach to the practice of the profession.

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Case Studies

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Case studies

1. A personal insulin pump– An embedded system in an insulin pump used by

diabetics to maintain blood glucose control.

2. A mental health case patient management system– A system used to maintain records of people

receiving care for mental health problems.

3. A wilderness weather station– A data collection system that collects data about

weather conditions in remote areas.

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1-A personal insulin pump

• A personal insulin pump is an external device that mimics the function of the pancreas.

• It uses an embedded sensor to measure the blood sugar level at periodic intervals and then injects insulin to maintain the blood sugar at a ‘normal’ level.

• I will draw on this example at various points in the course to illustrate aspects of critical systems engineering

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Insulin pump control system

• 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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Insulin pump hardware architecture

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Activity model of the insulin pump

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Concept of operation

• Using readings from an embedded sensor, the system automatically measures the level of glucose in the sufferer’s body.

• Consecutive readings are compared and, if they indicate that the level of glucose is rising (see next slide) then insulin is injected to counteract this rise.

• The ideal situation is a consistent level of sugar that is within some ‘safe’ band.

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Sugar Levels

• Unsafe– A very low level of sugar (arbitrarily, we will call this 3 units) is

dangerous and can result in “hypoglaecemia” which can result in a diabetic coma and ultimately death.

• Safe– Between 3 units and about 7 units, the levels of sugar are ‘safe’

and are comparable to those in people without diabetes. This is the ideal band.

• Undesirable– Above 7 units of insulin is undesirable but high levels are not

dangerous in the short-term. Continuous high-levels however can result in long-term side-effects.

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System Specification

• Functional specification– How to carry out the computation to determine if

insulin should be administered

• Dependability specification– Requirements to ensure safe operation of the pump

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Functional Specification

• If the reading is below the safe minimum, no insulin shall be delivered.

• If the reading is within the safe zone, then insulin is only delivered if the level of sugar is rising and the rate of increase of sugar level is increasing.

• If the reading is above the recommended level, insulin is delivered unless the level of blood sugar is falling and the rate of decrease of the blood sugar level is increasing.

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Dependability Specification

• Availability– The pump should have a high level of availability but the nature

of diabetes is such that continuous availability is unnecessary• Reliability

– Intermittent demands for service are made on the system• Safety

– The key safety requirements are that the operation of the system should never result in a very low level of blood sugar. A fail-safe position is for no insulin to be delivered

• Security– Not really applicable in this case

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Essential high-level requirements

• 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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2- A patient information system for mental health care

• 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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MHC-PMS

• 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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The organization of the MHC-PMS

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MHC-PMS key features• 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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MHC-PMS Concerns

• 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.

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Concern decomposition

• Concerns are decomposed into sub-concerns:• Concerns are decomposed into sub-concerns:

Information quality Information accuracy

Information timeliness

Information integrity

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The safety concern

Safety

Patient safety

Staff safety

Public safety

Mental Health Act

Accidental self-harm

Deliberate self-harm

Incorrect treatment

Adverse reaction to medication

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MHCPMS requirements

• The system shall provide fields in each patient record that allow details of incidents or threats of deliberate self-harm to be maintained

• The records of patients with a record of deliberate self-harm shall be highlighted to bring them to the attention of clinical system users

• The system shall only permit the transmission of personal patient information to accredited staff and to the patient themselves

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3- Wilderness weather station

• The government of a country with large areas of wilderness decides to deploy several hundred weather stations in remote areas.

• Weather stations collect data from a set of instruments that measure temperature and pressure, sunshine, rainfall, wind speed and wind direction.

• The weather station includes a number of instruments that measure weather parameters such as the wind speed and direction, the ground and air temperatures, the barometric pressure and the rainfall over a 24-hour period. Each of these instruments is controlled by a software system that takes parameter readings periodically and manages the data collected from the instruments.

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The weather station’s environment

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Weather information system

• The weather station system– This is responsible for collecting weather data, carrying out

some initial data processing and transmitting it to the data management system.

• The data management and archiving system– This system collects the data from all of the wilderness

weather stations, carries out data processing and analysis and archives the data.

• The station maintenance system– This system can communicate by satellite with all wilderness

weather stations to monitor the health of these systems and provide reports of problems.

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Essential system functionality

• Collect weather information from instruments at regular intervals

• Transmit this information, on request, to the weather information system over the satellite link

• Store information if communications are not available

• Monitor external conditions and shut down power generation/instruments if threat of damage from extreme weather

• Run regular diagnostic tests to assess overall health of system

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Additional software functionality

• Monitor the instruments, power and communication hardware and report faults to the management system.

• Manage the system power, ensuring that batteries are charged whenever the environmental conditions permit but also that generators are shut down in potentially damaging weather conditions, such as high wind.

• Support dynamic reconfiguration where parts of the software are replaced with new versions and where backup instruments are switched into the system in the event of system failure.

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The End