Object-Oriented
Software Quality
Engineering
Fall 2008
© Adapted from Dr. Deugo, Fall 2008
COMP 4004 – Lecture01
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Course Overview
© Adapted from Dr. Deugo, Fall 2008
COMP 4004 – Lecture01
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Logistics
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Instructor: Soheila Bashardoust
Office hours: Wednesdays 2:30-4:30PM @ HP5270
E-mail: sbtajali@scs.carleton.ca
Any relevant material to be put in:
www.scs.carleton/~sbtajali/4004
– slides will refer to (but not include) pictures of the textbook:
bring it to each lecture!
– slides will be posted on the course web-site every week
© Adapted from Dr. Deugo, Fall 2008
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Warnings!!
• Prereqs:
– you MUST have taken COMP 2004 and COMP 3004
» this course involves MODELING and Java expertise
• model creation will be VERY time consuming!
• there is fixing more than programming per se
• November 7'th: deadline to drop...
• Paul Menton Centre:
– Students with disabilities requiring academic accommodations
in this course are encouraged to contact a coordinator at the
Paul Menton Centre for Students with Disabilities to complete
the necessary letters of accommodation. After registering with
the Paul Menton Centre, make an appointment to meet and
discuss your needs with ME at least two weeks prior to the inclass final exam. This is necessary in order to ensure
sufficient time to make the necessary arrangements.
© Adapted from Dr. Deugo, Fall 2008
COMP 4004 – Lecture01
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Books
• Compulsory:
– R. Binder, Addison-Wesley, 2000
» Testing Object-Oriented Systems
» I repeat, I will be referring to BUT NOT POSTING the
figures of the book!
• Other useful design references:
– Hassan Gomaa, Addison-Wesley, 2000
» Designing concurrent, distributed real-time applications
with UML
– B. Douglass, Addison-Wesley, 1999
» Doing Hard Time
© Adapted from Dr. Deugo, Fall 2008
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Objectives of this Course
At the end of this course, you should:
• Have a good understanding of how to build
testable models.
– Roughly put, testable models are models from which tests can
be derived
• Have a basic understanding of the techniques
used to derived tests from testable models.
• Understand the issues involved in:
– testing classes (esp. in Java)
– maintaining traceability between testable models, code and
tests.
© Adapted from Dr. Deugo, Fall 2008
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Learning Method
• In the assignments, you will:
– develop testable models for a specific case study supplied by the
instructor
– study the Java code corresponding to the supplied models and
augment it with assertions (discussed late in the term)
– generate tests and execute test cases in order to validate this code
and verify it against the models you will have produced
» more on tests vs. test cases, validation vs. verification later!
– document traceability between models, code, tests and test cases
– investigate support for SQE in Eclipse
– time permitting:
» make necessary corrections and link them to previous versions
• In class, we will:
– study Binder ’s material
– ATTEMPT TO relate his material to the assignments!
© Adapted from Dr. Deugo, Fall 2008
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Course Deliverables
• Iteration 1: (test model creation and use) due Oct 20
– study models and code supplied for the J-Unit case study
– develop a suite of testable models
» this will require augmenting/correcting some of the supplied
models as well as developing other testable models
– produce a suite of tests for the validation and verification of the
system as a whole, as well as for a specific class
– select some test cases from these tests
• Iteration 2: (model/code-based testing)
due Nov 20
– develop a partial contract for specific classes
– investigate support for contracts, test cases, test models, test
strategies and traceability in Eclipse
– use all what you have learnt to test as much as possible the
supplied system: document tests and try to find faults!!
• Final Exam: open book exam on all material
discussed in the course...
© Adapted from Dr. Deugo, Fall 2008
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More Logistics
• Marking scheme:
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25% for the first iteration
25% for the second iteration
5% for presentation
45% for the final
• About marking:
– marking in this course is admittedly subjective:
» the responsibility is YOURS to provide all necessary
explanations… A posteriori arguments are not accepted!
» debates about marks will NOT be allowed
» marking will be relative to others and to ‘ planted ’ errors in the
material supplied by the instructor!
• Assignments may be done alone or preferably in pairs or triples!
– No consideration for vanishing members, work distribution, etc.
© Adapted from Dr. Deugo, Fall 2008
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And in the rest of this lecture
We shall:
• Motivate the importance of Software Quality
Engineering
• Give you an idea of what the viewpoint of this
course will be
• Overview what you should already have a basic
understanding of
© Adapted from Dr. Deugo, Fall 2008
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Crisis?
What Crisis?
Quality?
What Quality?
© Adapted from Dr. Deugo, Fall 2008
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Hardware vs Software
• Hardware costs are decreasing:
– hardware is fast and generally reliable
• Complexity is now mostly introduced at the
software level
• And software is constantly maintained and
evolved.
• Zero-defect programming is still a pious wish!
– only 0.3% faults on parachutes does not cut it...
– Formal (i.e., math based) approaches (in terms of
completeness and proofs) are used for safety-critical
applications.
• How are we doing with respect to quality in
general?
© Adapted from Dr. Deugo, Fall 2008
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Yourdon: The Reality of Software
• Software is commonly delivered late, way over
budget, and with unsatisfactory quality
• Software technologies are seldom evaluated
• Software development processes are unstable
and uncontrolled
• Software quality is poorly measured, monitored,
and controlled.
• Famous software failures are frequent:
– … read on ….
© Adapted from Dr. Deugo, Fall 2008
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Famous Software Bugs
• Therac-25 (1985-1987)
– Six people were overexposed during radiation treatments for cancer by
Canada's Therac-25 radiation therapy machine. Three of these patients
were believed to have died from the overdoses. The root cause was a lack
of quality assurance, which lead to an over-complex, inadequately tested,
under-documented system developed, and subsequently to the failure to
take adequate corrective action. (Pooley & Stevens, 1999)
• London Ambulance System (1992)
– A succession of software engineering failures, especially in project
management, caused 2 failures of London's (England) Ambulance dispatch
system. The repair cost was estimated at £9m, but it is believed that people
died who would not have died if ambulances had reached them as promptly
as they would have done without the failures.
• Denver baggage handling system
– The Denver airport baggage handling system was so complex (involving
300 computers) that the development overrun prevented the airport from
opening on time. Fixing the incredibly buggy system required an additional
50% of the original budget - nearly $200m.
© Adapted from Dr. Deugo, Fall 2008
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Famous Software Bugs
• Taurus (1993)
– Taurus, the planned automated transaction settlement system for
the London Stock Exchange was canceled after 5 years of failed
development. Losses are estimated at £75m for the project and
£450m to customers. (Pooley & Stevens, 1999)
• Ariane 5 (1996)
– The Ariane 5 rocket exploded on its maiden flight in June [4], 1996
because the navigation package was inherited from the Ariane 4
without proper testing. The new rocket flew faster, resulting in
larger values of some variables in the navigation software. Shortly
after launch, an attempt to convert a 64-bit floating-point number
into a 16-bit integer generated an overflow. The error was caught,
but the code that caught it elected to shut down the
subsystem. The rocket veered off course and exploded. It was
unfortunate that the code that failed genereated inertial reference
information useful only before lift-off; had it been turned off at the
moment of launch, there would have been no trouble. (Kernighan,
1999)
© Adapted from Dr. Deugo, Fall 2008
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Famous Software Bugs
• E-mail buffer overflow (1998)
– Several E-mail systems suffer from a "buffer overflow error", when
extremely long e-mail addresses are received. The internal buffers
receiving the addresses do not check for length and allow their buffers to
overflow causing the applications to crash. Hostile hackers use this fault to
trick the computer into running a malicious program in its place.
• USS Yorktown (1998)
– A crew member of the guided-missile cruiser USS Yorktown mistakenly
entered a zero for a data value, which resulted in a division by zero. The
error cascaded and eventually shut down the ship's propulsion
system. The ship was dead in the water for several hours because a
program didn't check for valid input. (reported in Scientific American,
November 1998)
• Mars Climate Orbiter (September 23rd, 1999)
– The 125 million dollar Mars Climate Orbiter is assumed lost by officials at
NASA. The failure responsible for loss of the orbiter is attributed to a
failure of NASA’s system engineer process. The process did not specify the
system of measurement to be used on the project. As a result, one of the
development teams used Imperial measurement while the other used the
metric system of measurement. When parameters from one module were
passed to another during orbit navigation correct, no conversion was
performed, resulting in the loss of the craft.
http://mars.jpl.nasa.gov/msp98/orbiter/
© Adapted from Dr. Deugo, Fall 2008
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• Books to read by Ed Yourdon :
– Death March: The Complete Developer’s Guide to Surviving
“Mission Impossible” Projects. Prentice-Hall, 1997
– Rise and resurrection of the American programmer, Prentice-Hall,
1996
© Adapted from Dr. Deugo, Fall 2008
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Yourdon’s Death March Projects
•
Definition 1: Project parameters exceed the norm by
>50% because of:
– Schedule compression (most common)
– Staff reduction
– Budget/resource constraints
– Functionality/performance demands
•
Definition 2: risk assessment (technical, legal,
political, etc.) indicates >50% chance of failure...
•
Observation: this is now the norm, not the exception!!
© Adapted from Dr. Deugo, Fall 2008
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Yourdon’s Explanations
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Politics, politics, politics: lack of culture of quality!!
Naive promises made by marketing, senior executives, project
managers, etc.
Naive optimism of youth: “we can do it over the weekend”
“Startup” mentality: we’ll go berserk for a few years
“Marine Corps” mentality: “real men don’t need sleep”
Intense competition caused by globalization of markets
Intense competition caused by appearance of new
technologies: CORBA and Java as complexity enabling…
Intense pressures caused by unexpected government
regulations
Unexpected and/or unplanned crises — e.g., your vendor went
bankrupt, or your 3 best programmers just died of Bubonic
Plague
© Adapted from Dr. Deugo, Fall 2008
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Why Software Engineering?
• We are always looking for recipes and tools for software
development.
• “It’s better than nothing” is a standard excuse to downplay
the flaws of current notations, methods and tools:
– there are some serious issues (e.g., the layout of statecharts, R.
Castello et al., Software - Practice and Experience, 2001) that should
question what the dominant paradigm suggests as a solution...
• In theory, we want to:
» do the right things
» do things right
» know that we have done the right things
» know that we have done things right
– In practice, first-to-market software will often gain acceptance, then
will condition its users to expect less, and finally will be eventually
improved to a point that is almost the right thing.
– In practice, most often, code IS the only reality, with models, if any,
quickly falling out of sync. And code and error fixing are usually still
the basis for your performance evaluation.
© Adapted from Dr. Deugo, Fall 2008
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About Software Engineering
• A huge field:
– “Software Engineering”, IEEE Computer Society, 1997
• A possible definition for Software Engineering from Tim
Lethbridge (UofO): :
– “Solving problems by the development of quality software within
cost, time and other constraints.”
• B. Douglass (“Doing Hard Time”) has a detailed OO
development process for real-time systems but has nothing to
directly say with respect to quality. Similarly, H. Gomaa has a
wonderful book about the design of OO real-time systems but
ignores quality issues altogether...
• D’Souza and Wills (“UML,components and framekworks: The
Catalysis Approach”) refer to the integrity of software as
meeting business requirements. They also value team
development and flexibility as key requirements for software.
• We are concerned in this course with what quality means and
how to achieve it?
© Adapted from Dr. Deugo, Fall 2008
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About Software Development
• Types of constraints:
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–
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Limited cost, time, supply of people, abilities of people
Inherent complexity of the task we tackle
Limitations of hardware, of compilers, of algorithms, etc.
Legacy code, processes, habits
• Human factors in quality emphasize the fact that software
development has a engineering and a social side:
– specific engineering decisions are often permeated by human biases
(wrt notation, use of patterns, use of O-T-Shelf components…, etc.)
• Software development as an investment:
– There are expected benefits, but also potential risks
– Pious wish: We should not compromise on quality even though we do
have constraints:
» But in fact, this compromise is omnipresent in the software
industry…
• The questions remain:
– What is quality software?
– What to do in order to obtain quality s/w?
© Adapted from Dr. Deugo, Fall 2008
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Definitions
• S/W Quality Engineering (SQE): The discipline of
specifying and controlling the quality of software
products
• S/W Management: The discipline of managing
projects to achieve quality within time constraints
and budget
• S/W (Quality and Productivity) Improvement: The
discipline of identifying weaknesses in current
S/W development practices and implement
improvements.
• Only SQE is the topic of this course!
– And in fact, we are even more specifically looking at the use of
test(able) models for testing code.
© Adapted from Dr. Deugo, Fall 2008
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About Quality Software
• According to Lethbridge:
– “Quality software is software that is sufficient in various aspects
such that utility over the maximum reasonable life-span is
maximized.”
– Utility is informally defined in terms of cost and productivity…
– Is this a useful definition? Sufficiency? Productivity?
• For Bob Probert (UofO):
– Quality should be defined using customer-directed terms
– Quality attributes must be measurable to some useful degree
during design, development and test.
• Aspects (or attributes) of quality include:
completeness, correctness, understandability,
usability, efficiency, reusability, maintainability, etc.
• If we had no constraints, we could, at least in theory,
achieve infinite quality…
– In reality, testing is almost unavoidably incomplete…
» see quote at the very beginning of Binder’s book...
© Adapted from Dr. Deugo, Fall 2008
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SQE and Measurement
• Usual ‘goals’ of SQE:
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Monitor and control quality and productivity
Predict and estimate quality and productivity
Understand and evaluate software development practices
Evaluate the impact of new technologies
• Monitoring, estimating, evaluating all depend on
the ability to measure...
© Adapted from Dr. Deugo, Fall 2008
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Typical Focus in SQE
Most authors concerned with quality emphasize
the importance of metrics and measurement:
• “You cannot control what you cannot measure”,
Tom DeMarco
• “Projects without clear goals won’t achieve their
goals clearly”, Tom Gilb
• “Measurement is the process by which numbers
or symbols are assigned to attributes of entities
in the real world in such a way to describe them
accordingly to clearly defined rules” Norman
Fenton
© Adapted from Dr. Deugo, Fall 2008
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Focus in this Course
• We will emphasize product quality engineering,
and downplay process issues and measurement.
– We will emphasize code testing against testable models.
• We will not emphasize:
– Software maintenance and evolution
» “Software Evolution”, L.J. Arthur, John Wiley & Sons, 1988
• Change management; impact analysis; corrective, adaptive, perfective
maintenance; reengineering, maintenance testing, configuration
management, managing maintenance
– Software release
» “Software release methodology”, M. Bays, PH, 1999:
• Source code control, builds, defect tracking, system integration,
change control, product release classification and numbering, release
distribution, service strategies, release management and planning
– The mathematics of the art of measurement:
» “The art of measurement”, R. Potter, HP, 2000
– Software Management and Software Improvement
© Adapted from Dr. Deugo, Fall 2008
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Pervasive SQE
• It is well documented that late errors can be
extremely expensive to fix.
– We will emphasize pervasive SQE via the use of testable models
» conversely, the dominant culture still reduces SQE to testing
as a phase at the end of the process…
» in practice, a lot of testing occurs after the product has been
released… SIGH!
• >65% (and up to 80%)of the software lifecycle is
spent in maintenance (ie testing, fixing, evolving…)
– The more statements need to be modified, the less successful the
fix or evolution will be…
– Some companies force rewrites when faced with hard-to-find,
hard-to-fix bugs…
• We will promote SQE activities in parallel with
design and code:
» design for testability and code for testability are NOT
dominant ideas at this point in time… Alas...
© Adapted from Dr. Deugo, Fall 2008
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SQE Texts (1)
• Software Verification and Validation
– S. Rakitin, Artech House, 1997
» Talks about the software crisis, the economic justification
of SQE, why a process for quality.
» Promotes an inspection process for requirements, design,
code and tests
» Addresses software quality metrics, configuration
management, testing, validation metrics and reliability very
concisely!
– Reflects what most companies will do at best…
• Customer Oriented Software Quality Assurance
– F. Ginac, PH, 1998
» Another short book that addresses SQE from a practical
viewpoint
» Touches on quality attributes and metrics; test methods,
types and tools; CMM and ISO 9000 appraisal of processes
© Adapted from Dr. Deugo, Fall 2008
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SQE Texts (2)
• Metrics and Models in Software Quality
Engineering
– S. H. Kan, Addison-Wesley, 1995
» Excellent discussion of process models and process
quality standards
» Good introduction to fundamentals of measurement
theory, software quality metrics, complexity metrics
» Includes more advanced and specific topics, such as
defect removal effectiveness, reliability growth models,
analyzing customer satisfaction
– Please note that Prof. Lionel Briand in Systems and
Engineering has a graduate course (94.579) on measurement.
He uses:
» N. Fenton, S. Pfleeger, Software Metrics: A Rigorous and Practical
Approach, PWS, 1996
» B. Kitchenham, Measurement for Process Improvement, 1995, out
of print
© Adapted from Dr. Deugo, Fall 2008
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Course Topics
• Introduction to the fundamental concepts,
terminology and techniques of SQE
• Exposure to the models and test derivation
techniques used in industry for object-oriented
testing:
– we are concerned with testable models and how to use them to
get tests and test cases
» why testable models? Because it is well documented that
most ( > 80%) errors are design-related errors…
» And code must be tested against models… rather than by
itself!
– we are concerned with code testing
– we are concerned with traceability (eg for regression testing)
© Adapted from Dr. Deugo, Fall 2008
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Quality
• What do we mean by Quality?
© Adapted from Dr. Deugo, Fall 2008
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The Timeless Way of Building
• Christopher Alexander, Oxford University Press,
1979, (Detailed Table of Contents, ix-xv)
• The Timeless Way
• A building or town will only be alive to the extent that
it is governed by the timeless way.
– 1. It is a process which brings order out of nothing but ourselves; it
cannot be attained, but it will happen of its own accord, if we will
only let it.
© Adapted from Dr. Deugo, Fall 2008
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The Quality
• To seek the timeless way we must first know the quality with out
a name
– 2. There is a central quality which is the root criterion of life and spirit in
man, a town, a building or a wilderness. This quality is objective and
precise, but it cannot be named.
– 3. The search which we make for this quality, in our own lives, is the central
search of any person, and the crux of any individual person's story. It is the
search for those moments and situations when we are most alive.
– 4. In order to define this quality in buildings and in towns, we must begin by
understanding that every place is given its character by certain patterns of
events that keep on happening there.
– 5. These patterns of events are always interlocked with certain geometric
patterns in space. Indeed, as we shall see, each building and each town is
ultimately made out of these patterns in the space, and out of nothing else;
they are the atoms and the molecules from which a building or town is
made.
© Adapted from Dr. Deugo, Fall 2008
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The Quality
• 6. The specific patterns out of which a building or a town is
made may be alive or dead. To the extent they are alive, they let
out inner forces loose, and set us free; but when they are dead,
they keep us locked in inner conflict.
• 7. The more living patterns there are in a place - a room, a
building, or a town - the more it comes to life as an entirety, the
more it glows, the more it has that self-maintaining fire which is
the quality without a name.
• 8. And when a building has this fire, then it becomes a part of
nature. Like ocean waves, or blades of grass, its parts are
governed by the endless play of repetition and variety created
in the presence of the fact that all things pass. This is the
quality itself.
© Adapted from Dr. Deugo, Fall 2008
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The Gate
• To reach the quality without a name we must then build a living
pattern language as a gate. 9. This quality in buildings and in
towns cannot be made, but only generated, indirectly, by the
ordinary actions of people, just as a flower cannot be made, but
only generated from the seed.
– 10. The people can shape buildings for themselves, and have done it for
centuries, by using languages which I call pattern languages. A pattern
language gives each person who uses it the power to create an infinite
variety of new and unique buildings, just as his ordinary languages gives
him the power to create an infinite variety of sentences.
– 11. These patterns languages are not confined to villages and farm society.
All acts of building are governed by a pattern language of some sort, and
the patterns in the world are there, entirely because they are created by the
pattern languages which people use.
– 12. And, beyond that, it is not just the shape of towns and buildings which
comes from pattern languages - it is their quality as well. Even the life and
beauty of the most awe-inspiring great religious buildings came from the
languages their builder used.
– 13. But in our time the languages have broken down. Since they are no
longer shared, the processes which keep them deep have broken down;
and it is therefore virtually impossible for anybody, in our time, to make a
building live.
© Adapted from Dr. Deugo, Fall 2008
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The Gate
– 14. To work our way towards a shared and living language once
again, we must first learn how to discover patterns which are deep,
and capable of generating life.
– 15. We may then gradually improve these patterns which we share,
by testing them against experience; we can determine, very simply,
whether these patterns make our surroundings live, or not, by
recognizing how they make us feel.
– 16. Once we have understood how to discover individual patterns
which are alive, we may then make a language for ourselves for any
building task we face. The structure of the language is created by
the network of connections among individual patterns: and the
language lives, or not, as a totality, to the degree these patterns
form a whole.
– 17. Then finally, from separate languages for different building
tasks, we can create a larger structure still, a structure of
structures, evolving constantly, which is the common language of a
town. This is the gate.
© Adapted from Dr. Deugo, Fall 2008
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The Way
• Once we built the gate, we can pass through it to the practice of the
timeless way.
•
– 18. Now we shall begin to see in detail how the rich and complex order of a town can
grow from thousands of creative acts. For once we have a common pattern language in
our town, we shall all have the power to make our streets and buildings live, through
our most ordinary acts. The language, like a see, is the genetic system which gives our
millions of small acts the power to form a whole.
– 19. Within this process, every individual act of building is a process in which space
gets differentiated. It is not a process of addition, in which preformed parts are
combined to create a whole, but a process of unfolding, like the evolution of an
embryo, in which the whole precedes the parts, and actually gives birth to them, by
splitting.
– 20. The process of unfolding goes step by step, one pattern at a time. Each step brings
just one pattern to life; and the intensity of the result depends on the intensity of these
individual steps.
– 21. From a sequence of these individual patterns, whole buildings with the character of
nature will form themselves within our thoughts, as easily as sentences.
– 22. In the same way, groups of people can conceive their larger public buildings, on the
ground, by following a common pattern language, almost as if they had a single mind.
© Adapted from Dr. Deugo, Fall 2008
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The Way
– 23. Once the buildings are conceived like this, they can be built,
directly, from a few simple marks made in the ground - again within
a common language, but directly, and without using drawings.
– 24. Next, several acts of building, each one done to repair and
magnify the product of the previous acts, will slowly generated a
larger and more complex whole than any single act can generated.
– 25. Finally, within the framework of a common language, millions of
individual acts of building will together generate a town which is
alive, and whole, and unpredictable, without control. This is a the
slow emergence of the quality without a name, as if from nothing.
– 26. And as the whole emerges, we shall see it take that ageless
character which gives the timeless way its name. This character is
a specific, morphological character, sharp and precise, which must
come into being any time a building or a town becomes alive: it is
the physical embodiment, in buildings, of the quality without a
name.
© Adapted from Dr. Deugo, Fall 2008
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The Kernel of the Way
• And yet the timeless way is not complete, and will
not fully generate the quality without a name, until we
leave the gate behind.
– 27. Indeed this ageless character has nothing, in the end, to do with
languages. The language, and the processes which stem from it,
merely release the fundamental order which is native to us. They
do not teach us, they only remind us of what we know already, and
of what we shall discover time and time again, when we give up our
ideas and opinions, and do exactly what emerges from ourselves.
© Adapted from Dr. Deugo, Fall 2008
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Appendix
Some Review
Material
(with an angle for testing)
(From 95.304…)
© Adapted from Dr. Deugo, Fall 2008
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Divide and Conquer Strategy
Faced with a complex problem our usual strategy
is to Divide and Conquer
• Break the problem into smaller, more manageable
sub-problems and solve them separately.
• There are different ways for dividing complex
problems into simpler problems:
-as steps or tasks to be carried out
-as assignment of responsibility
© Adapted from Dr. Deugo, Fall 2008
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SA/SD Modeling
• Modeling tackled the system or a subsystem
– testing was oriented towards testing of procedures (see next
slide)
• Three kinds of models were used:
– ER, DFD, FSM
• Each model being used offered a view of the
(sub)system being modeled as a whole:
– e.g., Hatley/Pirbhai and Ward/Mellor advocated one FSM for the
whole system
– FSMs are apparently excellent for testing…
» see Figure 7.3 p.182 for different FSM notations
• Semantically, it was not clear how the different
models being used should be integrated
– e.g., were your DFD and FSM consistent?
© Adapted from Dr. Deugo, Fall 2008
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Procedure Abstraction
Programs = Data Structures + Algorithms
Data
Procedure
Procedure
Procedure
Procedure
Procedure
Procedure
Procedure
© Adapted from Dr. Deugo, Fall 2008
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Data Abstraction
Procedures and Encapsulated Data
Stack
Procedure
Procedure
Queue
Procedure
Procedure
Employee
Procedure
Procedure
Procedure
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Modular Abstraction
Objects
Vehicle subclass: Car
start()
choke()
brake()
injectFuel()
accelerate()
unlockBrake()
steer()
serialNumber
engine
© Adapted from Dr. Deugo, Fall 2008
wheels
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Interacting Modules
Object-Orientation
Traffic Light
Procedure
Procedure
Car
Driver
Procedure
Procedure
Procedure
Procedure
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Main Models for OO
Requirements
Capture
Analysis
Design
© Adapted from Dr. Deugo, Fall 2008
Requirements
Models
Analysis
Models
Design
Models
Requirements Doc.
Scenario Descriptions
Domain Objects
Structure Model
Object Diagrams
CRC Cards
Scenario Model
Interaction
Diagrams
Behavior Model
Finite State
Machines
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A Few Facts
• Notations are merely syntax: they don’t say how.
– UML (Unified Modeling Language) is the dominant notation.
– We will study Binder ’s criticism of UML wrt testability!
• Methods edict rules:
– no heuristic, let alone no rule, holds for all situations
– OO system modeling is not a science but the realm of heuristics and
patterns
– Existing methods downplay validation and verification and generally
ignore traceability
• OO Assertional/Formal methods exist but:
– are not very user-friendly
– don’t necessarily scale up
– are not very object-oriented
» The semantics of inheritance complicates things!
– and yet are at the basis of a multitude of testing papers...
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Aiming for Traceability
• Boehm insists that a development process must not only be
iterative but also incremental.
• Traceability is required to achieve convergence:
– we must document the continuity that must exist between the workproducts of different activities.
– in turn, continuity enables completeness and consistency checks,
which are at the basis of validation and verification.
• Verification: Within a particular activity, the work-products
must be consistent:
– e.g., the structural, scenario and behavior models must be consistent
» For example, if an interaction diagram shows an object receiving a
message, then the FSM of this object must reflect this possibility
• Validation: Work-products must also be complete with
respect to the current requirements.
• Traceability is key to successful change impact analysis,
root cause analysis and regression testing.
© Adapted from Dr. Deugo, Fall 2008
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About Decoupling
Encapsulation:
• The right (??) responsibilities must be encapsulated, and
encapsulation must be respected
• Encapsulation should expose interface and hide implementation:
– is this good or bad news wrt testing??
More facets of Decoupling:
- Areas of responsibility should be decoupled from each other so
changes in one do not require changes in others
- this is good for testing
- Inheritance used in combination with dynamic binding for subtyping
SHOULD decouple an interface (parent) from its implementations
(subclasses). It may not…
- inheritance introduces challenges wrt testing...
- OO Design Patterns propose solutions to common OO design
problems. These solutions systematically emphasize decoupling.
But there is little to no consideration of testing...
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Testing and OOPLs
Detailed testing will have to address specifics of
an OOPL. For example, in Java/C++:
– You must declare the type of every variable
» Some type relaxation: base class pointer or reference can refer to
a derived class object and… there is casting...
– Fast and ‘safe’ (?) compilation
» Compile time error detection
» but can you debug it? And should it be a run-time
feature: this is a design error…
– Programmers allocate and de-allocate memory
» Implies a distinction between pointers and non-pointers
» Memory leaks and dangling references are frequent errors...
– C++ offers both static and dynamic method binding: don’t confuse with
dynamic typing!
» Dynamic binding introduces its own set of errors...
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