Software Engineering 2 lecture slide from roger pres man

1. Software Engineering (II)
Lecture 1
(Software Process & Project Metrics)
By
Abdur Rehman
Institute of Information Technology,
Kohat University of Science & Technology,
Kohat, KPK, Pakistan

2. •
Measurement is fundamental to any engineering
discipline, and soft-ware engineering is no exception.
•
Measurement enables us to gain insight by providing
a mechanism for objective evaluation.
[When you can measure what you are speaking about
and express it in numbers, you know something about it;
but when you cannot measure, when you cannot
express it in numbers, your knowledge is of a meager
and unsatisfactory kind]
Lord Kelvin

3. •
Software metrics refers to a broad range of
measurements for computer soft-ware.
•
Measurement can be used throughout a
software project to assist in estimation, quality
control, productivity assessment, and project
control.
•
Measurement can be applied to the software
process with the intent of improving it on a
continuous basis

4. Who does it ?
•
Software metrics are analyzed and assessed
by software managers. Measures are often
collected by software engineers.

5. Why is it important?
•
If you don’t measure, judgment can be based
only on subjective evaluation.
•
With measurement, trends (either good or
bad) can be spotted, better estimates can be
made, and true improvement can be
accomplished over time.

6. Measures, Metrics, And Indicators
•
Although the terms measure, measurement,
and metrics are often used interchange-ably,
there are subtle differences between them.
•
Because measure can be used either as a
noun or a verb, definitions of the term can
become confusing.

7. Measure
•
Within the software engineering context, a
measure provides a quantitative indication of
the extent, amount, dimension, capacity, or
size of some attribute of a product or process.
Measurement
•
It’s the act of determining a measure.

8. Metric
•
The IEEE Standard Glossary of Software
Engineering Terms defines metric as “a
quantitative measure of the degree to which a
system, component, or process possesses a
given attribute.”

9. Software Engineering (II)
Lecture 2
(Software Process & Project Metrics)
By
Abdur Rehman
Institute of Information Technology,
Kohat University of Science & Technology,
Kohat, KPK, Pakistan
9

10. 10
Quote
“Not everything that can be counted counts,
and not everything that counts can be
counted.”
Einstein
10

11. Definition
•
The IEEE Standard Glossary of Software
Engineering Terms defines metric as
“a quantitative measure of the degree to which
a system, component, or process possesses a
given attribute.”
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12. Metrics In The Process And Project
Domains
•
Measurement is commonplace in the engineering world.
We measure power consumption, weight, physical
dimensions, temperature, voltage etc.
•
Unfortunately, measurement is far less common in the
software engineering world.
•
We have trouble agreeing on what to measure and trouble
evaluating measures that are collected.
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13. Software Metrics Etiquette (Guidelines)
•
Use common sense and organizational sensitivity
when interpreting metrics data.
•
Provide regular feedback to the individuals and
teams who collect measures and metrics.
•
Don’t use metrics to assess individuals.
•
Work with practitioners and teams to set clear goals
and metrics that will be used to achieve them.
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14. •
Never use metrics to threaten individuals or teams.
•
Metrics data that indicate a problem area should not
be considered “negative.” These data are merely an
indicator for process improvement.
•
Don’t obsess on a single metric to the exclusion of
other important metrics.
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15. Software Engineering (II)
Lecture 3
(Direct and Indirect Metrics)
By
Abdur Rehman
Institute of Information Technology,
Kohat University of Science & Technology,
Kohat, KPK, Pakistan
15

16. •
Measurements in the physical world can be
categorized in two ways:
(a) direct measures (e.g., the length of a
Missile) (b)indirect measures (e.g., the "quality" of
Missile produced by counting the rejected ones)
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17. Direct Measures of The Software
Engineering
•
cost
•
effort applied.
•
lines of code (LOC) produced,
•
execution speed,
•
memory size,
•
defects reported over some set period of time
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18. Indirect Measures of The Software
Engineering
Indirect measures of the product include :
•
functionality
•
quality
•
complexity
•
efficiency
•
reliability
•
Maintainability
, and many other "–abilities
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19. Size Oriented Metric
19

20. •
The table lists each software development project that
has been completed over the past few years and
corresponding measures for that project.
e.g for project alpha reveals that :
•
12,100 lines of code were developed
•
with 24 person-months of effort
•
at a cost of $168,000
•
365 pages of documentation were developed
•
134 errors were recorded before the software was
released
•
29 defect were encountered after release to the
customer within the first year of operation
•
Three people worked on the development of software
for project alpha.
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21. From the basic data contained in the table, a set
of simple size-oriented metrics can be
developed for each project:
•
Errors per KLOC (thousand lines of code).
•
Defects per KLOC.
•
Cost per LOC.
•
Page of documentation per KLOC.
21

22. In addition, other interesting metrics can be
computed:
•
Errors per person-month.
•
LOC per person-month.
•
$ per page of documentation.
22

23. Software Engineering (II)
Lecture 4
(Software Quality Metrics)
By
Abdur Rehman
Institute of Information Technology,
Kohat University of Science & Technology,
Kohat, KPK, Pakistan
23

24. McCall and Cavano’s Framework for
Software Quality
•
It was presented in 1978.
•
These factors assess software from three
distinct points of view:
(1) product operation (using it)
(2) product revision (changing it), and
(3) product transition (modifying it to work in a
different environment; i.e., "porting" it)
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25. Measuring Quality
Correctness
•
Correctness is the degree to which the software performs
its required function.
•
The most common measure for correctness is defects per
KLOC, where a defect is defined as a verified lack of
conformance to requirements.
•
Defects are those problems reported by a user of the
program after the program has been released for general
use. For quality assessment purposes, defects are counted
over a standard period of time, typically one year
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26. Maintainability.
•
Software maintenance accounts for more effort than
any other software engineering activity.
•
Maintainability is the ease with which a program can
be corrected if an error is encountered, adapted if its
environment changes, or enhanced if the customer
desires a change in requirement.
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27. •
There is no way to measure maintainability directly;
therefore, we must use indirect measures.
•
A simple time-oriented metric is mean-time-to-
change(MTTC), the time it takes to analyze the
change request, design an appropriate modification,
implement the change, test it, and distribute the
change to all users.
•
On average, programs that are maintainable will
have a lower MTTC (for equivalent types of changes)
than programs that are not maintainable.
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28. Integrity
•
Software integrity has become increasingly
important in the age of hackers and firewalls.
•
This attribute measures a system's ability to with-
stand attacks (both accidental and intentional) to its
security.
•
Attacks can be made on all three components of
software: programs, data, and documents
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29. Usability
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30. •
It is interesting to note that nearly every
aspect of computing has undergone radical
change as the years have passed since McCall
and Cavano did their influential work in 1978.
•
But the attributes that provide an indication
of software quality remain the same.
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31. Software Engineering (II)
Lecture 5
(Software Quality Assurance)
By
Abdur Rehman
Institute of Information Technology,
Kohat University of Science & Technology,
Kohat, KPK, Pakistan
31

32. Quote
“People forget how fast you did a job but they
always remember how well you did it.”
Howard Newton
32

33. All the software engineering approaches
described strive to achieve a single goal:
to produce high-quality software
33

34. What is it?
•
You have to
(1) explicitly define what is meant when you say
“software quality,”
(2) create a set of activities that will help ensure that
every software engineering work product exhibits
high quality
(3) perform quality assurance activities on every
software project
(4) use metrics to develop strategies for improving
your software process and, as a consequence, the
quality of the end product
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35. Who does it?
Everyone involved in the
Software engineering process is responsible for
quality
35

36. Why is it important?
•
You can do it right, or you can do it over again.
•
If a software team stresses quality in all software
engineering activities, it reduces the amount of rework
that it must do.
•
That results in lower costs, and more importantly,
improved time-to-market.
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37. What are the steps?
•
Before software quality assurance activities can
be initiated, it is important to define ‘software
quality’ at a number of different levels of
abstraction.
•
Once you understand what quality is, a
software team must identify a set of SQA
activities that will filter errors out of work
products before they are passed on
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38. What is the work product?
•
A Software Quality Assurance Plan is created
to define a software team’s SQA strategy.
•
During analysis, design, and code generation,
the primary SQA work product is the formal
technical review summary report.
•
During testing, test plans and procedures are
produced.
•
Other work products associated with process
improvement may also be generated.
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39. How do I ensure that I’ve done it
right?
•
Find errors before they become defects! That
is, work to improve your defect removal
efficiency thereby reducing the amount of
rework that your software team has to
perform
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40. •
Some software developers continue to believe
that software quality is something you begin
to worry about after code has been
generated.
•
Instead Software quality assurance(SQA) is an
umbrella activity that is applied throughout
the software process.
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41. Software Engineering (II)
Lecture 6
(Software Quality Assurance – Continued)
By
Abdur Rehman
Institute of Information Technology,
Kohat University of Science & Technology,
Kohat, KPK, Pakistan
41

42. Quote
“It takes less time to do a thing right than
explain why you did it wrong”
Henry Wadsworth Longfellow
42

43. Quality Concepts
( 1) Quality
•
The American Heritage Dictionary defines quality as
“a characteristic or attribute of something”
•
As an attribute of an item, quality refers to measurable
characteristics.
•
Things we are able to compare to known standards such as
length, color, electrical properties etc.
•
However, software, largely an intellectual entity, is more
challenging to characterize than physical objects.
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44. software quality
software quality is defined as
“Conformance to explicitly stated functional and
performance requirements, explicitly documented
development standards, and implicit characteristics
that are expected of all professionally developed
software”
44

45. The definition serves to emphasize three important points:
1. Software requirements are the foundation from which
quality is measured. Lack of conformance to requirements is
lack of quality.
2. Specified standards define a set of development criteria
that guide the manner in which software is engineered. If the
criteria are not followed, lack of quality will almost surely
result.
3. A set of implicit requirements often goes unmentioned (e.g.,
the desire for ease of use and good maintainability). If
software conforms to its explicit requirements but fails to
meet implicit requirements, software quality is doubtful.
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46. (2) Quality Control
•
Quality control involves the series of inspections,
reviews, and tests used throughout the software
process to ensure each work product meets the
requirements placed upon it.
•
Quality control activities may be fully automated,
entirely manual, or a combination of automated
tools and human interaction.
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47. (3) Quality Assurance
•
The goal of quality assurance is to provide
management with the data necessary to be
informed about product quality, thereby
gaining insight and confidence that product
quality is meeting its goals.
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48. (4) Cost of Quality
•
The cost of quality includes all costs incurred in the
pursuit of quality or in performing quality related
activities.
•
Quality costs may be divided into costs associated
with
–
prevention,
–
appraisal, and
–
failure.
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49. Prevention costs include
• quality planning
• formal technical reviews
• test equipment
• training
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50. Appraisal costs
•
It include activities to gain insight into product
condition the “first time through” each process.
Examples of appraisal costs include
•
in-process and inter process inspection
•
equipment calibration and maintenance
•
testing
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51. Failure costs
•
It’s the cost that would disappear if no defects appeared
before shipping a product to customers.
•
Failure costs may be subdivided into internal failure costs and
external failure costs.
•
Internal failure costs are incurred when we detect a defect in
our product prior to shipment. Internal failure costs include
–
rework
–
repair
–
failure mode analysis
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52. External failure costs
•
These are associated with defects found after the
product has been shipped to the customer.
Examples of external failure costs are
–
complaint resolution
–
product return and replacement
–
help line support
–
warranty work
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53. As expected, the relative costs to find and repair a defect increase
dramatically as we go from prevention to detection to internal failure to
external failure costs.
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54. Another example:
•
Anecdotal data reported by Kaplan, Clark, and Tang
[KAP95] reinforces earlier cost statistics and is based
on work at IBM’s Rochester development facility:
•
A total of 7053 hours was spent inspecting 200,000
lines of code with the result that 3112 potential
defects were prevented. Assuming a programmer
cost of $40.00 per hour, the total cost of preventing
3112 defects was $282,120, or roughly $91.00 per
defect.
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55. •
Compare these numbers to the cost of defect removal
once the product has been shipped to the customer.
Suppose that there had been no inspections, but that
programmers had been extra careful and only one
defect per 1000 lines of code [significantly better than
industry average] escaped into the shipped product.
•
That would mean that 200 defects would still have to be
fixed in the field. At an estimated cost of $25,000 per
field fix, the cost would be $5 million, or approximately
18 times more expensive than the total cost of the
defect prevention effort.
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