Ethics and
10012 Things Every
Self-Respecting
Computer Scientist
Should Know
but might not learn in CS101-CS390
David Evans
evans@cs.virginia.edu
http://www.cs.virginia.edu/evans/cs390
Why This Isn’t a Research Pitch
• The students I want to work with are:
– Resourceful enough to learn about my
research by visiting my web page and
reading papers
– Smart enough to pick a thesis advisor by
talking to current/recent students
• I only have one hour and there are more
important things to tell you than about
my own research
– I may go over, feel free to leave at any time
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1001 Questions
0000 What is Computer Science?
0001 What problem did the first electronic programmable
computer solve?
0010 Why was the first “personal computer” built?
0011 Is Computer Science a science, engineering or other?
0100 What are the world’s most complex programs?
0101 How do Computer Scientists manage complexity?
0110 Who was the first object-oriented programmer?
0111 Who invented the Internet?
1000 Why should we say goodbye to “Hello World!”?
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0. What is
Computer Science?
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Let AB and CD be the two given numbers
not relatively prime. It is required to find the
greatest common measure of AB and CD.
If now CD measures AB, since it also
measures itself, then CD is a common
measure of CD and AB. And it is manifest
that it is also the greatest, for no greater
number than CD measures CD.
Euclid’s Elements, Book VII, Proposition 2 (300BC)
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The note on the inflected line is
only difficult to you, because it is so
easy. There is in fact nothing in it, but
you think there must be some grand
mystery hidden under that word
inflected!
Whenever from any point without
a given line, you draw a long to any
point in the given line, you have
inflected a line upon a given line.
Ada Byron (age 19), letter to Annabella
Acheson (explaining Euclid), 1834
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What is the
difference
between
Euclid and
Ada?
“It depends on what your
definition of ‘is’ is.”
Bill Gates (at Microsoft’s antitrust trial)
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Geometry vs. Computer Science
• Geometry (mathematics) is about
declarative knowledge: “what is”
If now CD measures AB, since it also measures itself,
then CD is a common measure of CD and AB
• Computer Science is about imperative
knowledge: “how to”
– About “computing” not “computers”
– An unnatural science
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Computer Science
“How to” knowledge:
• Ways of describing imperative
processes (computations)
Language
• Ways of reasoning about (predicting)
what imperative processes will do
Logic
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1. What problem did the first
electronic programmable
computer solve?
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Colossus
First Programmable Computer
• Bletchley Park, 1943
• Designed by Tommy
Flowers
• 10 Colossi in operation at
end of WWII
• Destroyed in 1960, kept
secret until 1970s
• (2 years before ENIAC –
calculating artillery tables)
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Colossus’ Problem
• Decode Nazi high
command messages
from Lorenz Machine
• XOR encoding:
Ci = Mi  Ki
– Perfect cipher, if K is
random and secret
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Why perfectly secure?
For any given ciphertext, all plaintexts are
equally possible.
Ciphertext:
Key:
Plaintext:
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0100111110101
1
1100000100110
B
1000111010011
= “CS”
0
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Breaking Lorenz
• Operator and receiver need
same keys
• Generate key bits using rotor
machine, start with same
configuration
• One operator retransmitted a message (but
abbreviated message header the second
time!)
• Enough for Bletchley Park to figure out key –
and structure of machine that generated it!
• But still had to try all configurations
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Colossus
• Read ciphertext and Lorenz wheel
patterns from tapes
• Tried each alignment, calculated
correlation with German
• Decoded messages (63M letters by 10
Colossus machines) that enabled Allies
to know German troop locations to plan
D-Day
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2. Why was the first personal
computer built?
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Apollo Guidance Computer, 1961-69
1 cubic foot,
70 pounds
4KB of read/write
magnetic core
memory
64KB of read-only
memory
Why did they need to fit the
guidance computer in the rocket?
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AGC History
• Needed all guidance to be on board in
case Soviets jammed signals for Earth
• Design began in 1961
• Risky decision to use Integrated Circuits
(invented in 1958)
– Building 4 prototypes used 60% of all ICs
produced in the US in the early 60s!
– Spurred industry growth
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3. Science, Engineering or
Other?
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Science?
• Understanding Nature through
Observation
– About real things like bowling balls, black
holes, antimatter, electrons, comets, etc.
• Math and Computer Science are about
fake things like numbers, graphs,
functions, lists, etc.
– Computer Science is a useful tool for doing
real science, but not a real science
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Engineering?
“Engineering is design under
constraint… Engineering is synthetic
- it strives to create what can be, but it
is constrained by nature, by cost, by
concerns of safety, reliability,
environmental impact,
manufacturability, maintainability and
many other such 'ilities.' ...”
William Wulf
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Computing Power 1969-2002
(in Apollo Control Computer Units)
4500000
4000000
Moore’s Law: computing power
doubles every 18 months!
3500000
3000000
2500000
If Apollo Guidance
Computer power is 1
inch, you have 5 miles!
(1GB/4KB = 262144)
2000000
1500000
1000000
500000
22
2002
2001
1999
1998
1996
1995
1993
1992
1990
1989
1001 Things
1987
1986
1984
1983
1981
1980
1978
1977
1975
1974
1972
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1971
1969
0
Constraints Computer Scientists Face
• Not like those for engineers:
– Cost, weight, physics, etc.
– If 8 Million times what NASA had in 1969 isn’t
enough for you, wait until 2006 and you will
have 32 Million times…
• More like those for Musicians and Poets:
– Imagination and Creativity
– Complexity of what we can understand
– Cost of human effort
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So, what is computer science?
• Science
– No: its about fake things like numbers, not
about observing and understanding nature
• Engineering
– No: we don’t have to deal with engineeringtype constraints
Must be a Liberal Art!
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The Liberal Arts
Trivium (3 roads)
Grammar
Rhetoric
Quadrivium (4 roads)
Logic Arithmetic
Music
Geometry
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Astronomy
25
Liberal Arts
Quadrivium
Trivium
Yes, we need to understand
• Grammar: study of meaning in
meaning to describe
written expression
computations
• Rhetoric: comprehension of verbal Interfaces between
components, discourse
and written discourse
between programs and users
• Logic: argumentative discourse for Logic for controlling
and reasoning about
discovering truth
computations
• Arithmetic: understanding numbers
Yes
• Geometry: quantification of space
Yes (graphics)
• Music: number in time
Yes (read Gödel,
• Astronomy: laws of the planets and
Escher, Bach)
stars
Yes, read Neil DeGrasse Tyson’s essay
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4. What are the world’s most
complex programs?
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Complex Programs
• Apollo Guidance Software
– ~36K instructions
• F-22 Steath Fighter Avionics Software
– 1.5M lines of code (Ada)
• 5EEE (phone switching software)
– 18M lines
• Windows XP
– ~50M lines (1 error per kloc ~ 50,000 bugs)
• Anything more complex?
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Human Genome
Produces
60 Trillion Cells (6 * 1013)
50 Million die every second!
Today is the 50th anniversary
of the most important scientific
paper of the 20th century!
Molecular structure of Nucleic
Acids, James Watson and
Francis Crick. Letter to Nature,
sent 2 April 1953 (2 pages)
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How Big is the
Make-a-Human Program?
• 3 Billion Base Pairs
– Each nucleotide is 2 bits (4 possibilities)
– 3B bases * 1 byte/4 pairs = 750 MB
1 CD ~ 650 MB
Wal-Mart’s database
is 280 Terabytes
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Encoding is Redundant
• DNA encodes proteins
• Every sequence of 3 base pairs one of 20
amino acids (or stop codon)
– 21 possible codons, but 43 = 64 possible values
– So, really only 750GB * (21/64) ~ 246 MB
• Trillions of creatures, over millions of years,
had to die to create this program!
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Expressiveness of DNA
• Genetic code for 2 humans differs in
only 2 million bases
– 4 million bits = 0.5 MB
1/3 of a floppy disk
<1% of Windows 2000
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5. How do Computer
Scientists manage
complexity?
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Abstraction
Adapted from Gerard Holzmann’s FSE Slides
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Abstraction in Computer Science
• Procedural Abstraction (CS101)
– Abstract what to do from specific values to do
it to
• Data Abstraction (CS201)
– Abstract away representation details by
specifying what you can do with something
• Abstraction by Specification (CS340)
– Abstract away how details by saying what a
procedure does
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6. Who was the first
Object-Oriented
Programmer?
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What is an Object?
• Packaging state and procedures
– state: the rep
• What a thing is
– procedures: methods and constructors
• What you can do with it
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Bjarne Stroustrup’s Answer
“Object-oriented programming is programming
with inheritance. Data abstraction is
programming using user-defined types. With few
exceptions, object-oriented programming can and
ought to be a superset of data abstraction. These
techniques need proper support to be effective.
Data abstraction primarily needs support in the
form of language features and object-oriented
programming needs further support from a
programming environment. To be general
purpose, a language supporting data abstraction
or object-oriented programming must enable
effective use of traditional hardware.”
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“I invented the
term
Object-Oriented
and I can tell you I
did not have C++
in mind.”
Alan Kay
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• Object-Oriented Programming is a state of
mind where you program by thinking about
objects
• It is difficult to reach that state of mind if your
language doesn’t have:
– Mechanisms for packaging state and procedures
• Java has class
– Subtyping
• Java has extends (subtype and subclass) and
implements (subtype)
• Other things can help: dynamic dispatch,
implementation inheritance, automatic memory
management, mixins, good Indian food, Krispy
Kremes, etc.
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Who was the first
object-oriented programmer?
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By the word operation, we mean any process which
alters the mutual relation of two or more things, be
this relation of what kind it may. This is the most
general definition, and would include all subjects in
the universe. Again, it might act upon other things
besides number, were objects found whose mutual
fundamental relations could be expressed by those of
the abstract science of operations, and which should
be also susceptible of adaptations to the action of the
operating notation and mechanism of the engine.
Supposing, for instance, that the fundamental
relations of pitched sounds in the science of harmony
and of musical composition...
Ada Byron, 1843
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7. Who Invented the Internet?
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What is a Network?
A group of three or more connected
entities communicating indirectly
Ancient Greeks had beacon chain
networks on Greek island mountaintops
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Chappe’s Semaphore Network
First Line (Paris to Lille), 1794
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Mobile Semaphore Telegraph
Used in the Crimean War 1853-1856
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internetwork
A collection of multiple networks
connected together, so messages can
be transmitted between nodes on
different networks.
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The First Internetwork
• 1800: Sweden and Denmark worried about
Britain invading
• Edelcrantz proposes link across strait
separating Sweden and Denmark to connect
their (signaling) telegraph networks
• 1801: British attack Copenhagen, transmit
message to Sweden, but they don’t help.
• Denmark signs treaty with Britain, and stops
communications with Sweden
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First Use of The Internet
• October 1969: First packets on the
ARPANet from UCLA to Stanford.
Starts to send "LOGIN", but it crashes
on the G.
• 20 July 1969:
Live video (b/w) and
audio transmitted from
moon to Earth, and to
several hundred
televisions worldwide.
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Licklider and Taylor’s Vision
Available within the network will be functions and services to
which you subscribe on a regular basis and others that you
call for when you need them. In the former group will be
investment guidance, tax counseling, selective dissemination
of information in your field of specialization, announcement of
cultural, sport, and entertainment events that fit your
interests, etc. In the latter group will be dictionaries,
encyclopedias, indexes, catalogues, editing programs,
teaching programs, testing programs, programming systems,
data bases, and – most important – communication, display,
and modeling programs. All these will be – at some late
date in the history of networking - systematized and
coherent; you will be able to get along in one basic
language up to the point at which you choose a
specialized language for its power or terseness.
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J. C. R. Licklider and Robert W. Taylor, The Computer
as a Communication Device, April 1968
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The Modern Internet
• Packet Switching: Leonard Kleinrock (UCLA)
thinks he did, Donald Davies and Paul Baran,
Edelcrantz’s signalling network (1809) sort of
did it
• Internet Protocol: Vint Cerf, Bob Kahn
• Vision, Funding: J.C.R. Licklider, Bob Taylor
• Government: Al Gore (first politician to promote
Internet, 1986; act to connect government networks
to form “Interagency Network”)
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9. Why should we say
“goodbye” to
“Hello World!”?
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A C++ Program
// Canonical first program
// Dana Wahoo, January 15, 2003, version 1
#include <iostream>
#include <string>
using namespace std;
int main() {
cout << "Hello world! " << endl;
return 0;
}
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Goodbye “Hello World”
• Doesn’t compute anything
– Computers exist for computing things
• Makes an easy human task tedious
– Computers are supposed to automate
tedious tasks, not make easy tasks tedious
• Makes simple things mysterious
– Even after finishing CS101 and CS201, very
few students could explain everything in it!
(even without counting the #include’d files)
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Components of a C++ Program
// Canonical first program
Comments
// Dana Wahoo, January 15, 2003, version 1
#include <iostream>
Cruft to keep compiler happy
#include <string>
Mysterious magic
using namespace std;
constants
int main() {
cout << "Hello world! " << endl ;
return 0 ;
}
Mysterious
meaningless
return value
2 April 2003
Mysterious overloaded operator that
breaks abstraction barriers
(are both <<’s the same?)
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Summary
• Computer Science is a real intellectual
discipline: not like “Automotive
Engineering” or “Toaster Science”
• Computer Science is the subject most
consistent with the traditional Liberal Arts
offered at UVa today
• Biology became part of CS 50 years ago
today
• Al Gore really did create the Internet
• Goodbye “Hello World!”
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Any Questions?
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