Transcript Definition(s) of Software Engineering

Definition(s) of Software
Engineering
Establishment and use of sound
engineering principles to obtain
economically software that is reliable
and works on real machines efficiently.
(Fritz Bauer)
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Definition(s) of Software
Engineering (cont’d)
(i) Application of a
systematic, disciplined,
quantifiable approach to
the development,
operation and
maintenance of software;
that is, the application of
engineering to software.
(ii) The study of approaches
as in (i). (IEEE 93)
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• By “systematic” we mean:
Following a well-defined sequence of activities,
- in which desired outputs (deliverables) are well-defined
- by using well-defined inputs
(i.e. documented syntax, semantics, context and other relevant properties of the input)
- in a well-defined process
(e.g. using organizational standards for interprocess communication, data formats, error
handling etc.)
- whose outputs are in turn used similarly as inputs in subsequent process(es),
- until the final output is achieved,
- and where the correctness of the output is verifiable.
Note: The “inputs” and “outputs” most often refer to requirements, software
specifications, the software itself, documentation, test inputs/outputs and similar
software artifacts.
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By “disciplined” we mean:
• Each process is followed using
organizational principles (e.g. who manages
whom, who is responsible for what?),
• Intermediate results are carefully
documented, as well as final results,
• Actions are traceable as to their causes,
individuals involved, time of occurrence
and circumstances.
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By “quantifiable” we mean:
• The size and extent of the required effort
(size of output code, data, documentation,
manpower, duration, budget for development,
expected error rate and user support)
are predictable within justifiable and acceptable
bounds
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What SWE is not:
• Just “programming” or
“coding”
• System engineering (in a
broad sense)
although software engineers may
be called upon to participate in
system engineering analyses
• Software salesmenship
although they may be called upon
to help analyze customer needs
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Why Do We Need SWE?
To make the production of software
• easier
• more disciplined and predictable
• more economical.
•
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Evolution of Software Technology
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Operating systems
Languages
Development tools
Database and networking technology
Project management tools
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Evolution of machine architecture
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Improvement of machine instruction sets
Invention mass storage devices
Machine interrupt schemes
Much larger physical memories
Virtual memory (paging)
Cache memory
Fault-tolerant computing
Parallel and multi-processing
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Evolution of Systems
Interconnection
• Local area networking
(peer-to-peer and hierarchical connection,
servers)
• Wide area networking
(dial-up and fixed connections)
• Networking architecture
• Communication protocols
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Database Systems
• From simple sequential “files” to
“databases”
• Indexed files
• Hierarchical databases
• Network-style databases
• Relational databases
• More recently, object-oriented
databases
• Database management systems
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Decreasing Hardware Costs
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Ever smaller and faster components
More reliable
Requiring less energy
More easily replaceable
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Increasing Demand
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Improved user interfaces
Cheaper and faster machines
Increase in application areas
Improved connections
Most recently the Internet!
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Differences between Software
Engineering and Hardware Engineering
• Software is developed or engineered, not
manufactured.
• Software doesn’t wear out (in the usual
sense).
It is updated or replaced with a new version.
• Most software tends to be custom-built
eventhough there is a movement toward componentbased assembly.
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Hardware Failure Pattern
“Bathtub Curve”
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Software Failure Pattern
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Examples of Application Areas
• System software
(Operating systems, compilers, databases, graphics
packages, communication ...)
• Real-time software
Interacts with external events
Has tight timing requirements
Requires high-security, reliability and availability
Often mission-critical (can not be allowed to fail)
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Application Areas (cont’d)
• Business Software
Ranging from simple to very complex
Requiring its own expert knowledge
Very large files
Needs telecommunication, devices like
point-of-sale (POS) terminals
Highly organized computer organization
and personnel (esp. in large
companies)
Very detailed records covering long
periods
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Engineering and Scientific Software
• Complex formula evaluation
• Very high accuracy
• Interaction with data collection devices
(e.g. Sensors) often at high speeds
• High resolution graphic displays of large
amounts of data
• Parallel and multi-processor applications
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Embedded Software
• Software embedded in non-computer
devices (e.g. cars, planes, cell phones,
home appliances such as refrigerators)
through special-purpose processors
• Must be resistant to failures, tough
climactic conditions, rough handling
• Often optimized to require least memory
and still maintain speed
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Military Software
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Often real-time
Engineering/scientific
Including embedded components
High-technology (communications)
High security and error control (reliability)
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Video Game Software
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Graphic and artistic content
Video-type action
Very high timing requirements
High-sped user interaction
Graphics and sound integrated
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Artificial Intelligence Software
Involves:
Problem solving,
Complex symbolic programming
(e.g. pattern recognition, theorem proving, virtual
reality concepts, game playing etc.)
Physical system control (e.g. Robotic arm-leg
movement)
Vision, sound/voice recognition
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Web-based Applications
• General public information (news, info about
organizations and society)
• Business-to-consumer communication
(product promotions, sales)
• Business-to-business communication
• Electronic mail
• “Surfing”
• Seach engines
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Building Blocks of Software Engineering
Tools
Methods
Process
QUALITY FOCUS
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The Generic SWE Approach
• What is the problem to be solved?
-- The most important question of all...
-- Do we have sufficient detail ?
-- Do we really know what the customer
wants?
-- Does he agree that that’s what he
wants?
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More questions ...
• How will the solution be realized?
How shall we test the solution once it is
constructed?
How shall we maintain the system and
support the users in the short and long
terms?
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The Software Development
Process
The Software Development Process (also
called the Software Process) is the process used
to answer the above questions, dealing
with:
• Definition of the problem
• Analysis of the problem
• The conception and development of a
design
• Implementation of the design
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The Software Development Process
(cont’d)
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Testing
Documentation
User Training (if required)
Maintenance and support
Enhancement of the product (if required).
The Software Development Process
(cont’d)
The sequence and extent of activities
needed to carry out the above process
varies depending on:
• How well the user (customer)
understands his own needs
• How well the developers know the
application area
The Software Development Process
(cont’d)
• Resources available for the project (time,
technology, money, people)
• The type of project (internal/external, level of
secrecy, amount of documentation, user support
required etc)
• The developer organization
... And many other factors
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