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Software Engineering Introduction - Computer Science · Introduction Department of Computer...
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Based on Presentation by Nurit Gal-oz, Department of Computer Science Ben-Gurion university Mira Balaban Department of Computer Science Ben-Gurion university Igor Potapov: http://www.csc.liv.ac.uk/~igor/COMP201
Ian Sommerville: http://www.comp.lancs.ac.uk/computing/resources/IanS/SE7/Presentations/index.htmlAlexander Borgida: http://www.cs.rutgers.edu/~borgida/431/
Software Engineering
Introduction
Department of Computer Science, Ben-Gurion University
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מנהלה
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What is software?
Computer programs and associated documentation
Software products may be developed for a particular customer or may be developed for a general market
Software products may be Generic - developed to be sold to a range of different customers
Bespoke (custom) - developed for a single customer according to their specification
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What is Engineering?
Application of a systematic, disciplined, quantifiable approach to
structures,
machines,
products,
systems,
processes.
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IEEE Standard Glossary of Software Engineering Terminology,” IEEE std 610.12-1990, 1990
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What is Software Engineering? Software Engineering is that form of engineering that applies
• a systematic disciplined quantifiable approach• the principles of computer science, design, engineering, management,
mathematics, psychology, sociology, and other disciplines as necessary• and sometimes just plain invention
tocreating, developing, operating and maintaining cost-effective, reliably correct, high-quality solutions to software problems
[Definition by Berry 92]
SE requires
the identification of a problem,
a computer to carry execute a software product, and
a user environment (composed of people, tools, methodologies, etc.)
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Software Engineering - Motivation
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The task of software engineers?
Software engineers should
adopt a systematic and organised approach to their
work
use appropriate tools and techniques depending on
the problem to be solved,
the development constraints and
the resources available
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Origin of Software Engineering?
Software engineering deals with the development ofhigh-quality software systems.
Software engineering is abstract – no physical limitations:
leads to unlimited complexity.
Software engineering – coined in 1968: within discussion of software crisis. The NATO conference, 1968 in Garmisch, Germany In response to the perception that computer programming had not kept up
with advances in computer hardware.
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HELP WANTED!
One of the most significant developments in
the computer industry during the 1960s was
the perceived shortage of skilled “computer
people”
The programmer personnel crisis is the first
of the many “software crises” that were
proclaimed over the next several decades.
The first published use of the phrase
“software crisis” appears in a 1966
Business Week article on the “shortage of
programmers”“Software Gap: A Growing Crisis for Computers,” Business Week, November 5, 1966, 127
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What is the “software crisis”?
Major projects are meaningfully late.
Software costs more than predicted.
Software is unreliable.
Software is difficult to maintain.
Poor performance.
While hardware costs were decreasing, software costs were rising.
requires techniques to control the
complexity of large software systems.
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Standish Group’s CHAOS 2009 Report
Successful -projects delivered on time, on budget, with required features and functions.
Challenged - late, over budget, and/or with less than the required features and functions.
Failed - cancelled prior to completion or delivered and never used.
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Standish Group’s CHAOS 2014 Report
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NASA’s Mars Climate Orbiter Project
In 1999 a Mars space probe from NASA was ‘lost’
Two teams involved in the space probe development were using different systems of measurement
Lockheed Martin engineering team used English units of measurement while the NASAs team used the more conventional metric system for a key spacecraft operation
Reasons: There had been inadequate consideration of the entire mission and its post-launch
operation as a total system
Communications and training within the project had been inconsistent
There was no complete end-to-end verification of navigation software and related computer models
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NASA's Mars Polar Lander
Actions taken subsequently for another project, NASA's Mars
Polar Lander
a new senior management leader was assigned
work plans were freshly reviewed and augmented
detailed fault tree analyses took place for pending mission events
daily teleconferences took place to evaluate technical
progress and plan work yet to be done
independent peer review of all operational and
contingency procedures was introduced
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Reasons
The scope of the project had not been matched to the
funding, leading to inadequate funding for defined
outcomes.
Poor communication between, rather than within, different
teams.
There was inadequate risk management and issue control.
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HealthCar.gov
Now
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HealthCar.gov
Two Years ago
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מה קורה אצלנו
:מקור 2014, הטכניון, ר עמיר תומר"ד, ניהול פרויקטי תוכנה
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מביכים נוספים הקשורים בתוכנהאירועים
טכניון, 2014תוכנה שיטות בהנדסת , עמיר תומר' פרופ: מקור20
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Unrealistic or unarticulated project goals
Inaccurate estimates of needed resources
Badly defined system requirements
Poor reporting of the project’s status
Unmanaged risks
Poor communication among customers, developers, and users
Use of immature technology
Inability to handle the project’s complexity
Sloppy development practices
Poor project management
Stakeholder politics
Commercial pressuresCharette, R. N., Why Software Fails?, IEEE Spectrum, Vol. 42,
Issue 9, Sept. 2005
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Programming in the small
One programmer
understands everything from top to bottom.
Main problem is the
development of algorithms
Programming in the large
System is developed by a
large teams of programmers
Main problems are management of details and
communication between software subsystems
Defines software system in terms of components and interactions among those components
Programming in the Small and
Programming in the Large
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Why Software Engineering is Needed?
Software development is hard !
Important to distinguish “easy” systems (one developer, one user, experimental use only) from“hard” systems (multiple developers, multiple users, products).
Experience with “easy” systems is misleading: One person techniques do not scale up.
Analogy with bridge building: Over a stream = easy, one person job.
Over a big River … ? (the techniques do not scale) `
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Why is SE hard? real world problems:
Requirements are not clear and “acceptability” is defined by user satisfaction
For example: “software to help people control nuclear reactors”
As opposed to problems where there are pre-stated specifications (e.g. ,“write a program to find the shortest path...”), where it makes sense to talk about the correctness of a solution
wicked problems: define and solve concurrently no unique definition or solution always room for improvement in def’n and sol’n new problem, not previously encountered many stakeholders, with different goals
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Success Factors
Size of team
Type of Development
Methodologies, Process, Staff Skill, Tools and delivery
Highly skilled executive sponsor
Highly engaged users who thoroughly know their subject Matter
Focus on high value items instead of providing on low value
items just for the sake of political appeasement
Quick Decision making and cooperative peers who can
ensure working together as team to achieve a common goal
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BUT: The Software Werewolf
Software is like a werewolf—it looks normal until the moon
comes out and it turns into a monster
Missed deadlines
Blown budgets
Buggy software
We want the silver bullet to kill the
monster
something to make software costs drop as
rapidly as computer hardware costs do.
Frederick P. Brooks:No Silver Bullaet: Essence and Accidents of Software Engineering
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There Is No Silver Bullet! Frederick P. Brooks: “As we look to the horizon of a decade hence, we see no silver bullet.
There is no single development, in either
essence, technology or in management technique,
that by itself promises even one order-of-magnitude improvement in productivity, in reliability, in
simplicity”
Frederick P. Brooks, No Silver Bullet: Essence and Accidents of
Software Engineering
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Essential Difficulties of SE: [Brooks] COMPLEXITY:
• software is more complex for its size than any other human construct;
no two parts are alike (vs. car, microchips,...);
• science advances by simplifying, while software cannot ignore/simplify details of real world
• CONFORMITY:• among {hardware, software, people, organizations} it is software which is chosen to bend or
adapt because it is more malleable, last to arrive on the scene, usually only one developed on site,...
• CHANGEABILITY:• once delivered, most engineered products (hardware, cars, buildings) are rarely changed
because the cost to change would be a large fraction of the cost to make. The (unfortunate) perception is that software is cheap to change. And pressure to change comes from successful use, and aging hardware platform.
• INVISIBILITY:• since it has no physical reality, software is not properly visualizable with diagrams, etc. in the
way in which houses, circuits, etc are.
Frederick P. Brooks:No Silver Bullaet: Essence and Accidents of Software Engineering
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Complexity
Software is more complex for their size then an others human
construction.
Many problems of developing software products derive from this
essential complexity and its nonlinear increases with size.
http://www.informationisbeautiful.net/visualizations/million
-lines-of-code/
The increase in size makes communication among team members
hard.
Problem are: product flaws, cost overruns, schedule delays.
Are not only technical problems, management problems too.
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Complexity
טכניון, 2014תוכנה שיטות בהנדסת , עמיר תומר' פרופ: מקור
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Conformity Conformity comes from the fact that all new software must conform to the way things
where done in the past, because it is hard to change everyone.
Main reason software must conform is that it is new on the scene.
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Changeability Being able to change something after it has been constructed is a new concept.
Software must be able to change, and the complexity of the systems becomes harder to
follow.
All successful software gets changed.
Successful software also survives beyond the normal life of the machine vehicle for which
it is first written for.
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Invisibility
Software has no 3-D way on which it can be laid out.
Software does not have one map or graph, it will have multiple
maps and graphs.
Communication becomes hard because each person my see it a
different way.
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The software product is intangible
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Why Software Engineering Is Hard?
The main problem is complexity
Many sources, but size is key:
UNIX contains 4 million lines of code
Windows 2000 contains 108 lines of code
Software engineering is about managing this
complexity.
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What will (not) make a big difference: [Brooks1987]
• Minor• Ada or Java or C# or Python or ...• Object-Oriented Programming• Artificial Intelligence• Automatic Programming• Graphical programming• Program verification• Environments and tools• Workstations
• Major• Buy vs build• Requirements refinement and prototyping• Incremental development• Great designers (Unix, Pascal,Smalltalk vs Cobol,PL/I.Ada,MS-DOS)
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Complex software systems Advances in hardware and network technologies have paved the way for
the development of increasingly pervasive software-based systems of systems Operate in distributed and embedded computing environments consisting
of diverse devices personal computers, specialized sensors and actuators Communicate using a variety of interaction paradigms
e.g., SOAP messaging, media streaming),
Dynamically adapt to changes in operating environments, Behave in a dependable manner
Despite significant advances in programming languages and supporting integrated development environments (IDEs), developing these complex software systems using current code-centric technologies requires herculean effort.
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Software Project Secrets: Why Software
Projects Fail
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No Silver Bullet Reloaded Retrospective
OOPSLA Panel 2007
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Bottom line (by Berry)
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I no longer get excited over any new language, development model, method,
tool, or environment that is supposed to improve programming…
…The most important work is addressing requirements, changes, and the
psychology and sociology of programming
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HighLearn vs. Moodle
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משולש האילוצים ברגע שמכניסים שינויים
אי אפשר לרצות את כל שלושת האילוצים
בעלי ענין חייבים להחליטאילו שניים חשובים יותר
Software Project Management- Fall 2016
SCE Dr. Azzam Maraee43
Software Project Management- Fall 2016 SCE Dr. Azzam Maraee
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SE: Processes, Models, and Tools Processes:
Systematic ways of organizing teams and tasks so that there is a clear, traceable path from customer requirements to the final product (e.g. Waterfall, Prototyping, Spiral, etc.)
Processes help organize and co-ordinate teams, prepare documentation, reduce bugs, manage risk, increase productivity, etc.
Models: Well-defined formal or informal languages and techniques for organizing and
communicating arguments and decisions about software. e.g: specification languages (Z, etc) design models (UML, etc)
Models help stake-holders communicate: customers with developers, designers and developers, developers and testers etc.
If they are formal, they also can help support automation
Tools: Programs which automate or otherwise support software development tasks: e.g., Eclipse,
Make, CVS, etc. Tools increase productivity, quality and can reduce costs
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What is a software process? A structured set of activities required to develop a
software system
Generic activities in all software processes are:
Specification - what the system should do and its development 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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Software Engineering Activities1. Problem statement
• needs analysis• requirements specification: functional, non-functional
2. Design • architectural• detailed• (communication, database)
3. Implementation• coding• testing:• module• integration• documentation
4. Maintenance• corrective• adaptive• enhancement
Specification
Development
Validation
Evolution
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What is a software process model? An abstract representation of a process
It presents a description of a process from some particular perspective
Examples of process perspectives: Workflow perspective represents inputs, outputs and dependencies. Data-flow perspective represents data transformation activities. Role/action perspective represents the roles/activities of the
people involved in software process.
Generic process models: Waterfall
Separate and distinct phases of specification and development Evolutionary development
Specification, development and testing are interleaved Iterative Development Formal transformation
A mathematical system model is formally transformed to an implementation Integration from reusable components
The system is assembled from existing components
In practice applied for
the design and implementation phase of software development
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What is CASE ? (Computer-Aided Software Engineering)
Software systems which are intended to provide automated
support for software process activities, such as requirements
analysis, system modelling, debugging and testing.
Upper-CASE
Tools to support the early process
activities of requirements and design.
Lower-CASE
Tools to support activities such as
programming, debugging and testing.
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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
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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The attributes of good software? The software should deliver the required functionality and
performance to the user and should be maintainable, dependable, efficient and usable
Maintainability Software must evolve to meet changing needs.
Dependability Software must be trustworthy.
Efficiency Software should not make wasteful use of system resources.
Usability Software must be usable by the users for which it was designed.
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Software engineering as a discipline
within computer science
Computer science theories are currently insufficient to act as a
complete underpinning for software engineering, BUT
it is a foundation for practical aspects of software engineering
Computer Science Software Engineering
is concerned with
theory
fundamentals
the practicalities of developing
delivering useful software
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SWEBOK-הידעגוף–תוכנההנדסת
טכניון, 2014תוכנה שיטות בהנדסת , עמיר תומר' פרופ: מקור
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What is the difference between software
engineering and system engineering?
Software engineering is part of System engineering
System engineering is concerned with all aspects of computer-based systems development including hardware, software and process engineering
System engineers are involved in
system specification,
architectural design,
integration and deployment
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What are the key challenges facing
software engineering?
Software engineering in the 21st century faces three key challenges:
Heterogeneity Systems are distributed and include a mix of hardware and software.
Legacy systems (old valuable systems) must be maintained, updated and integrated into new systems.
Delivery There is an increasing pressure for faster delivery of software.
Trust Software must be trusted by its naive users.
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Professional and ethical responsibility (1)
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.
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Issues of professional responsibility (2)
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.
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Issues of professional responsibility (3)
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, say) to
extremely serious (dissemination of viruses).
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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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Code of ethics - 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.
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Code of ethics - principles
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.
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Code of ethics - principles
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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Ethical dilemmas
Disagreement in principle with the policies of senior
management.
Your employer acts in an unethical way and releases a safety-critical
system without finishing the testing of the system.
Participation in the development of military weapons systems or
nuclear systems.
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Summary: Key points (1) Software engineering is an engineering discipline that is concerned
with all aspects of software production.
Software products consist of developed programs and associated documentation. Essential product attributes are maintainability, dependability, efficiency and usability.
The software process consists of activities that are involved in developing software products. Basic activities are software specification, development, validation and evolution.
Methods are organised ways of producing software. They include suggestions for the process to be followed, the notations to be used, rules governing the system descriptions which are produced and design guidelines.
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Summary: Key points (2) CASE tools are software systems which are designed to support
routine activities in the software process such as editing design
diagrams, checking diagram consistency and keeping track of program
tests which have been run.
Software engineers have responsibilities to the engineering
profession and society. They should not simply be concerned with
technical issues.
Professional societies publish codes of conduct which set out the
standards of behaviour expected of their members.
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The Software Process
A structured set of activities required to develop a
software system
Specification
Analysis, design and implementation.
Validation
Evolution
A software process model is an abstract representation of a
process
A general approach for organizing a project into activities;
It presents a description of a process from some particular perspective
An aid to thinking, not a rigid prescription of the way to do things
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Waterfall ModelRequirements
definition
System andsoftware design
Implementationand unit testing
Integration andsystem testing
Operation andmaintenance
• Inflexible partitioning of the
project into distinct stages
• Difficult to respond to changing
customer requirements
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מפל "של מודל ( הצפוי)ומותו ( התמוהים)חייו "המים
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Incremental Development
Incremental development is a staging and scheduling strategy in which
various parts of the system are developed at different times or rates, and
integrated as they are completed.
The alternative strategy to incremental development is to develop the
entire system with a “big bang” integration at the end.
Using both incremental and iterative development © Alistair Cockburn 2008
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Incremental Development – Version I
פיתוח•אחזקה•
הפעלה מבצעית
פרישה
הקמתמימושמימושמימוש(build)מבנה
1,2,...,n
אימותדרישות
אימותניתוח
אימותארכיטקטורה
הנדסת מערכת
תכן מפורט
מימוש
שילוב
בדיקות
מסירה
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Incremental Development – Version II
ניתוח
תכן
מימושושילוב
מסירה
2מבנה ניתוח
תכן
מימושושילוב
מסירה
קבוצת ניתוח
קבוצת תכן
קבוצת מימוש
1מבנה
ניתוח
תכן
מימושושילוב
מסירה
nמבנה
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Iterative Development
Iterative development is a rework scheduling strategy in which time is
set aside to revise and improve parts of the system.
The alternative strategy to iterative development is to plan to get
everything right the first time.
Using both incremental and iterative development © Alistair Cockburn 2008
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Iterative Development
There are two particular, specialized rework strategies:
Develop the system as well as possible, in the thinking that if it is done
sufficiently well, the changes will be relatively minor and can be
incorporated quickly
Develop the least amount possible before sending out for evaluation, in the
thinking that less work will be wasted when the new information arrives.
Mona Liza example
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Incremental means adding, iterative
means reworking (by Alistair Cockburn)
Incremental development is a staging and scheduling strategy in which the various
parts of the system are developed at different times or rates and integrated as they are
completed. The alternative is to develop the entire system with a big bang integration at the
end.
Iterative development is a rework scheduling strategy in which time is set aside to
revise and improve parts of the system. The alternative development is to get it right the
first time (or at least declare that it is right!).
http://www.stickyminds.com/BetterSoftware/magazine.asp?fn=cifea&id=108
Increment Iterate
fundamentally means “add onto”.fundamentally means “change”.
repeating the process on a new section
of work.
repeating the process on the same
section of work
repeat the process (, design,
implement, evaluate),
repeat the process (, design,
implement, evaluate),
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Spiral model (Boehm 88)
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Agile
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What is an Agile method? Focus on the code rather than the design.
Based on an iterative approach to software development.
Intended to deliver working software quickly.
Evolve quickly to meet changing requirements.
There are claims that agile methods are probably best suited to small/medium-
sized business systems or PC products.
More active customer involvement needed
Considered People-based rather than Plan-based
Several agile methods
Extreme Programming (XP) most popular
No single definition -Agile Manifesto (2001) closest to a definition
Set of principles
Developed by Agile Alliance
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The players in the game are “People”
Weak on: Strong on:
Consistency Communicating
Discipline Looking around
Following instructions Copy / modifying
Motivated by:
Pride in work
Pride in contributing
Pride in accomplishment
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Summary of Principles of agile methods
Principle Description
Customer involvement The customer should be closely involved throughout the
development process. Their role is provide and prioritise new
system requirements and to evaluate the iterations of the system.
Incremental delivery The software is developed in increments with the customer
specifying the requirements to be included in each increment.
People not process The skills of the development team should be recognised and
exploited. The team should be left to develop their own ways of
working without prescriptive processes.
Embrace change Expect the system requirements to change and design the system
so that it can accommodate these changes.
Maintain simplicity Focus on simplicity in both the software being developed and in
the development process used. Wherever possible, actively work
to eliminate complexity from the system.
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What are the Agile Methodologies?eXtreme Programming has received the most attention, but here is a list:
XP SCRUM
DSDM
The Crystal Family ASD FDD dX (agile RUP)
Open Source
Agile Modeling Pragmatic Programming
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eXtreme Programming
Development and delivery of very small increments of
functionality.
Relies on constant code improvement, user involvement in
the development team and pair wise programming.
Emphasizes Test Driven Development (TDD) as part of the
small development iterations.
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Claimed Problems with agile methods
It can be difficult to keep the interest of customers who are
involved in the process.
Team members may be unsuited to the intense involvement
that characterizes agile methods.
Prioritising changes can be difficult where there are multiple
stakeholders.
Maintaining simplicity requires extra work.
Contracts may be a problem as with other approaches to
iterative development.
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Problems with incremental development
(from a waterfall eye…) Management problems
Progress can be hard to judge and problems hard to find because there is no documentation to demonstrate what has been done.
Contractual problems The normal contract may include a specification; without a specification,
different forms of contract have to be used.
Validation problems Without a specification, what is the system being tested against?
Maintenance problems Continual change tends to corrupt software structure making it more
expensive to change and evolve to meet new requirements.
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Understanding Organizations
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Structural frame: Focuses
on roles and responsibilities,
coordination and control.
Organization charts help
define this frame.
Human resources frame:
Focuses on providing
harmony between needs of
the organization and needs of
people.
Political frame: Assumes
organizations are coalitions
composed of varied
individuals and interest
groups. Conflict and power
are key issues.
Symbolic frame: Focuses on
symbols and meanings
related to events. Culture is
important.
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Model-Driven-Engineering (MDE)
MDE =
Software development by repeated transformations of models
Motivation
Growing complexity requires multiple levels of abstraction not
supported by programming languages
Technologies
Domain specific modeling languages (DSMLs)
Transformation engines
Model level development platforms
EMF, MetaEdit, Epsilon
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SE Research
Academic Legitimacy of the Software Engineering Discipline (Daniel M. Berry)
Occasionally, a researcher gets an idea for a new approach that may seem
ridiculous to others, who discount it. However, in any area of active
research, it is dangerous to discount any approach that has a reason that it
might work and that has not been specifically disproved.
No one can know ahead of time whether or not the approach will
work. If we discount an approach that would have worked, we are cutting
ourselves off from a benefit. Ultimately, we cannot discount anything that
might yield a solution, anything reasonable that has not been
demonstrated not to have any impact on the process or the software.
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