01 fse software&sw-engineering
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B. Computer Sci. (SE) (Hons.)
CSEB233: Fundamentals of Software Engineering
Software & Software Engineering
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Lesson Objectives
Define ‘Software’ Discuss issues related to Software
Define ‘Software Engineering’ (SE) Describe Polya’s Four Essence of SE
Practices Explain Hooker’s Seven SE Principles Discuss several myths of SE
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Software & Software Engineering
What is Software?
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What is Software?
Software is developed or engineered, it is not manufactured in the classical sense
Software does not "wear out" Although the industry is moving toward
component-based construction, most software continues to be custom-built
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Wear vs. Deterioration
idealized curve
change
actual curve
Failurerate
Time
increased failurerate due to side effects
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Software Applications
System software Application software Engineering/scientific software Embedded software Product-line software WebApps (Web applications) AI software
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Software — New Categories
Open world computing pervasive, distributed
computing Ubiquitous computing
wireless networks Netsourcing
the Web as a computing engine
Open source “free” source code open to
the computing community a blessing, but also a
potential curse! Also
Data mining Grid computing Cognitive machines Software for
nanotechnologies
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Legacy Software
Why must it change? Software must be adapted to meet the needs of
new computing environments or technology Software must be enhanced to implement new
business requirements Software must be extended to make it
interoperable with other more modern systems or databases
Software must be re-architected to make it viable within a network environment
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Characteristics of WebApps - I
Network Intensiveness A WebApp resides on a network and must serve the needs of a
diverse community of clients Concurrency
A large number of users may access the WebApp at one time Unpredictable load
The number of users of the WebApp may vary by orders of magnitude from day to day
Performance If a WebApp user must wait too long (for access, for server-side
processing, for client-side formatting and display), he or she may decide to go elsewhere
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Characteristics of WebApps - II
Availability Although expectation of 100 percent availability is unreasonable, users of
popular WebApps often demand access on a “24/7/365” basis. Data driven
The primary function of many WebApps is to use hypermedia to present text, graphics, audio, and video content to the end-user.
Content sensitive The quality and aesthetic nature of content remains an important
determinant of the quality of a WebApp. Continuous evolution
Unlike conventional application software that evolves over a series of planned, chronologically-spaced releases, Web applications evolve continuously.
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Characteristics of WebApps - III
Immediacy Although immediacy—the compelling need to get software to
market quickly—is a characteristic of many application domains, WebApps often exhibit a time to market that can be a matter of a few days or weeks
Security Because WebApps are available via network access, it is
difficult, if not impossible, to limit the population of end-users who may access the application
Aesthetics An undeniable part of the appeal of a WebApp is its look and
feel
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Software & Software Engineering
What is Software Engineering?
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Software Engineering
Some realities: a concerted effort should be made to understand
the problem before a software solution is developed
design becomes a pivotal activity software should exhibit high quality software should be maintainable
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Software EngineeringThe Seminal Definition
Software engineering is The establishment and use of sound
engineering principles in order to obtain economically, software that is reliable and works efficiently on real machines
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Software EngineeringThe IEEE Definition
Software Engineering The application of a systematic, disciplined,
quantifiable approach to the development, operation, and maintenance of software; that is, the application of engineering to software
The study of approaches as described above
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A Layered Technology
Software Engineering
a “quality” focus
process model
methods
tools
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A Process Framework
Framework activities work tasks work products milestones & deliverables QA checkpoints
Umbrella Activities
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Framework Activities
Communication Planning Modeling
Analysis of requirements Design
Construction Code generation Testing
Deployment
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Umbrella Activities
Software project management Formal technical reviews Software quality assurance Software configuration management Work product preparation and production Reusability management Measurement Risk management
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Adapting a Process Model
the overall flow of activities, actions, and tasks and the interdependencies among them
the degree to which actions and tasks are defined within each framework activity
the degree to which work products are identified and required
the manner which quality assurance activities are applied
the manner in which project tracking and control activities are applied
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Adapting a Process Model
the overall degree of detail and rigor with which the process is described
the degree to which the customer and other stakeholders are involved with the project
the level of autonomy given to the software team
the degree to which team organization and roles are prescribed
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Software & Software Engineering
Four Essence of SE Practices
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The Essence of SE Practices
Polya suggests: Understand the problem
♦ communication and analysis Plan a solution
♦ modeling and software design Carry out the plan
♦ code generation Examine the result for accuracy
♦ testing and quality assurance
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The Essence of SE Practices1. Understand the Problem
Who has a stake in the solution to the problem? Who are the stakeholders?
What are the unknowns? What data, functions, and features are required to
properly solve the problem? Can the problem be compartmentalized?
Is it possible to represent smaller problems that may be easier to understand?
Can the problem be represented graphically? Can an analysis model be created?
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The Essence of SE Practices 2. Plan the Solution
Have you seen similar problems before? Are there patterns that are recognizable in a potential solution? Is there existing software that implements the data, functions,
and features that are required? Has a similar problem been solved?
If so, are elements of the solution reusable? Can sub-problems be defined?
If so, are solutions readily apparent for the subproblems? Can you represent a solution in a manner that leads to
effective implementation? Can a design model be created?
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The Essence of SE Practices 3. Carry Out the Plan
Does the solution conform to the plan? Is source code traceable to the design model?
Is each component part of the solution provably correct? Has the design and code been reviewed, or
better, have correctness proofs been applied to algorithm?
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The Essence of SE Practices4. Examine the Result
Is it possible to test each component part of the solution? Has a reasonable testing strategy been
implemented? Does the solution produce results that
conform to the data, functions, and features that are required? Has the software been validated against all
stakeholder requirements?
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Software & Software Engineering
Seven General Principles of SE
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Hooker’s General Principles
The Reason It All Exists KISS (Keep It Simple, Stupid!) Maintain the Vision What You Produce, Others Will Consume Be Open to the Future Plan Ahead for Reuse Think!
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Hooker’s General Principles1. The Reason It All Exists
Software exists to provide value to its users All decisions should be made with this in
mind
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Hooker’s General Principles2. Keep It Simple (KISS)
There are many factors to consider in any design effort
Thus, all software design should be as simple as possible but not simpler to ease understanding and maintenance of the software
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Hooker’s General Principles3. Maintain the Vision
A clear vision is essential to the success of a software project
Compromising the architectural vision of a software system weakens and break even well-designed systems
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Hooker’s General Principles4. What You Produce, Others Will Consume
Consume use, maintain, document or depend on
Always specify, design, and implement knowing others will have to understand what you are doing
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Hooker’s General Principles5. Be Open to the Future
True “industrial-strength” software must endure long lifetime
Hence, design the software to: solve the general problem, not just the specific
one, be ready to adapt to changes (in hardware,
computing platform etc.), and be reused
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Hooker’s General Principles6. Plan Ahead for Reuse
Reuse reduces the cost and increases the value of the reused components and the systems into which they are incorporated
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Hooker’s General Principles7. Think
When you think about something (placing clear, complete thought before action), you are more likely to do it right (more importantly, the first time).
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Software & Software Engineering
Software Myths
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Software Myths
Software myths – erroneous beliefs about software and the process that is used to build it
Misleading attitudes that have caused serious problems for managers and practitioners
Classifications of software myths: Management Customer Practitioner
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Software MythsManagement
Myth: We already have a book that’s full of standards and
procedures for building software Won’t that provide my people with everything they
need to know? Reality:
The book of standards may exist, but is it used? Are practitioners’ aware of its existence? Does it reflect modern SE practices? Is it complete? Is it adaptable?
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Software Myths Customer
Myth: Software requirements continuously change, but change
can be easily accommodated because software is flexible Reality:
The impact of change varies with the time at which it is introduced
The cost of impact of changes in early stage of software project is relative small
However, changes introduced at a later development stage may require a lot of resources and major design modification
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Software MythsPractitioner
Myth: “Once we write the program and get it work, our
job is done.” Reality:
Somebody once said the “the sooner you begin ‘writing the code’, the longer it’ll take you to get done.”
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How It all Starts
Every software project is precipitated by some business need the need to correct a defect in an existing
application; the need to adapt a ‘legacy system’ to a changing
business environment; the need to extend the functions and features of an
existing application, or the need to create a new product, service, or
system.
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Summary
Definitions of software and software engineering
Software deteriorates but never wear out Several software application domain – system
software, engineering/scientific software, AI software, embedded software, etc.
The Polya’s Four Essence of SE Practices Understand the problem; Plan a solution; Execute
the plan; Examine the result for accuracy
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Summary
Seven SE Principles The Reason It All Exists; KISS; Maintain the
Vision; What You Produce, Others Will Consume; Be Open to the Future; Plan Ahead for Reuse; Think!
Software myths have caused serious problems for the software industry
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THE ENDCopyright © 2013
Mohd. Sharifuddin Ahmad, PhD
College of Information Technology