CMSC 100
Course Overview
Professor Marie desJardins
Thursday, August 30, 2012
CMSC 100 -- Overview
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Thurs 8/30/12
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CMSC 100 -- Overview
wordle.net
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Overview
 Who
am I?
 What
is Computer Science?
 Course
 First
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CMSC 100 -- Overview
Logistics
Assignments
 UPC/QR
Code Example
Thurs 8/30/12
Who am I?
CMSC 100 -- Overview
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Thurs 8/30/12
About the Instructor
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
Prof. Marie desJardins
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A.B. Engineering, Harvard 1985

Ph.D. Computer Science, Berkeley 1992

Research Scientist, SRI, 1991-2001

Professor at UMBC 2001-now
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Tenured in 2007; promoted to Professor in 2011
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Married since 1985, two daughters (ages 16 (junior in high school)
and 18 (sophomore in college))
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Like to read, do crossword puzzles, sing, play the piano, cook, ski,
travel, eat great food
Class Intro 1/30/11
My Research
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Artificial intelligence
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How to get computers to behave in ways that we would consider to be
“intelligent”

Machine learning: Making computers adaptable and able to improve
their performance over time
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Planning: Enabling computers to make decisions and solve problems

Multi-agent systems: Getting computers to interact effectively with each
other and with humans
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Class Intro 1/30/11
Research Projects
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
Integrating low-level learning and planning to enable “skill
bootstrapping” (the ability to layer successively more complex skills
on top of each other to solve hard problems)

Modeling trust in dynamic real-world environments like supply
chain management
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Analyzing planning problems to construct libraries of contingency
plans for rapid replanning
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Preference learning to discover users’ preferences in online rating
systems and other applications
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Learning from sparse data, and understanding uncertainty in
learned models
Class Intro 1/30/11
What is Computer
Science?
CMSC 100 -- Overview
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Thurs 8/30/12
The Computer Revolution

How fast did this happen?

[ http://www.blinkenlights.com/pc.shtml ]
1950: “Simon” (plans published in Radio Electronics)
1973: HP 65 (programmable calculator)
1975: Altair 8800 (first widely used programmable computer kit)
1977: Apple II (a huge breakthrough, the first mass-produced, inexpensive
personal computer)
1981: IBM 5150 PC (now we’re really taking off)

1984: Apple Macintosh 128K (my first computer!!)

2008: MacBook Air
(my newest computer!)
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Moore’s Law

Computer memory
(and processing speed,
resolution, and just
about everything else)
increases exponentially

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(roughly: doubles every
18-24 months)
Source: wikipedia
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Measuring Memory

One 0/1 (“no/yes”) “bit” is the basic unit of memory

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How many different patterns can you represent with one bit of
storage?
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Eight (23) bits = one byte
1,024 (210) bytes = one kilobyte (1K)*
1,024K (220 bytes) = one megabyte (1M)
1,024K (230 bytes) = one gigabyte (1G)
1,024 (240 bytes) = one terabyte (1T)
1,024 (250 bytes) = one petabyte (1P)
... 280 bytes = one yottabyte (1Y?)
Two! (It’s either 0 or 1; that’s it, no in between)
How many different patterns can you represent with one byte of storage?
* Note
CMSC 100 -- Overview
that external storage is usually measured in decimal rather than binary (1000 bytes = 1K, and so on)
Thurs 8/30/12
What Was It Like Then?
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The PDP-11/70s I used in college had 64K of RAM, with hard disks that
held less than 1M of external storage
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... and we had to walk five miles, uphill, in the snow, every day! And we had to live
in a cardboard box in the middle of the road!
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What Is It Like Now?
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The PDP-11/70s we used in college had 64K of RAM, with hard disks that held
less than 1M of memory

The cheapest Dell Inspiron laptop ($399.99) has 4G of RAM and a 50G
hard drive.... [twice as much as the capacities I mentioned when I last taught this
course, just three years ago...]

...a factor of 1018 more RAM and 1013 more disk space
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...and your iPod nano has 8G (or 16G!) of blindingly fast storage

...so don’t come whining to me about how slow your computer is!
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It’s Not Just Speed, It’s
Quantity

So just how big a revolution are we talking about?

How many computers do you think were in the room when I took my first
programming class?

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Answer: ZERO.
How many computers are in this room?
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Grand Challenges for CS
Information Search
Information Integration
Autonomous
Vehicles
Human-Level Intelligence
Smart Matter
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http://www.cs.cmu.edu/~claytronics/software/
CMSC 100 -- Overview
thebrain.mcgill.ca
Thurs 8/30/12
How Does a Computer
Work?
“The work performed by the computer is specified by a program, which is
written in a programming language. This language is converted to sequences of
machine-language instructions by interpreters or compilers, via a predefined set
of subroutines called the operating system. The instructions, which are stored
in the memory of the computer, define the operations to be performed on data,
which are also stored in the computer's memory. A finite-state machine fetches
and executes these instructions. The instructions as well as the data are
represented by patterns of bits. Both the finite-state machine and the memory
are built of storage registers and Boolean logic blocks, and the latter are based
on simple logical functions, such as And, Or, and Invert. These logical
functions are implemented by switches, which are set up either in series or in
parallel, and these switches control a physical substance, such as water or
electricity, which is used to send one of two possible signals from one switch to
another: 1 or 0. This is the hierarchy of abstraction that makes computers
work.”
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-- W. Daniel Hillis, The Pattern on the Stone
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How Does a Computer
Work?
“The work performed by the computer is specified by a program, which is
written in a programming language. This language is converted to sequences of
machine-language instructions by interpreters or compilers, via a predefined set
of subroutines called the operating system. The instructions, which are stored in
the memory of the computer, define the operations to be performed on data,
which are also stored in the computer's memory. A finite-state machine fetches
and executes these instructions. The instructions as well as the data are
represented by patterns of bits. Both the finite-state machine and the memory
are built of storage registers and Boolean logic blocks, and the latter are based
on simple logical functions, such as And, Or, and Invert. These logical functions
are implemented by switches, which are set up either in series or in parallel, and
these switches control a physical substance, such as water or electricity, which is
used to send one of two possible signals from one switch to another: 1 or 0. This
is the hierarchy of abstraction that makes computers work.”
-- W. Daniel Hillis, The Pattern on the Stone
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Abstraction: The Key Idea!
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Computers are very complex
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Most interesting programs are very complex
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What makes it possible to design and maintain these complex systems??
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Which just means:
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Once we’ve solved a “low-level detail,” we can treat that solution as
a “black box” with known inputs and outputs, and not worry about
how it works.
The way we get there is called problem reduction (or decomposition or
divide-and-conquer)
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Course Overview and
Policies
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What This Class is About
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How computers are built, programmed, and used to solve problems
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Hardware: Digital logic and system architecture
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Systems: Operating systems and networks
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Software: Basic programming/algorithms, databases
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Theory: Algorithms, computation, complexity
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Applications: AI, graphics, …
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Social issues: Ethics, privacy, environmental impact
Other skills emphasized:

Effective writing and presentation skills
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Basic programming (in Scratch)
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Foundational mathematics for computer science
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What this class is NOT
about
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How to install Windows or Linux
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How to use Excel and PowerPoint
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What kind of computer you should buy
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Advanced programming techniques
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Course Logistics
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Instructor: Prof. Marie desJardins, mariedj@cs.umbc.edu
http://www.csee.umbc.edu/~mariedj/
Office hours: Tues 2:30-3:30, Wed 2:00-3:00, ITE 337
TAs (ITE 349):
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CMSC 100 -- Overview
Clay Alberty, clay2@umbc.edu
Office hours: Mon 2:30-4:30pm
Kellie LaFlamme, kl4@umbc.edu,
Office hours: Tues/Thurs 11:30-12:30pm
Stephanie Schneider, sschneider713@gmail.com
Office hours: Wed 4-5pm
Course website/syllabus:
http://www.csee.umbc.edu/courses/undergraduate/100/Fall12/
Schedule:
http://www.csee.umbc.edu/courses/undergraduate/100/Fall12/schedul
e.html
Thurs 8/30/12
Textbook
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CMSC 100 -- Overview
Schneider and Gersting, Invitation to Computer Science, 6/e
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About half of the reading in the book will be
assigned, as will many chapter exercises
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I’ve requested a reserve copy to be placed
on reserve at the library

You can buy it on Amazon for $84.44 (less
than the bookstore is charging...)
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You can buy the ebook for $76.49 at the
Cengage website
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Buy an earlier edition at your own risk!
It’s your responsibility to have access to the
6th edition content and exercises
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Does anybody already have the 5th edition?
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My Expectations
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Students will…
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Attend class regularly
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Be prompt, and not engage in distracting or disruptive behaviors
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NO LAPTOPS OR CELLPHONES (INCLUDING TEXTING)
DURING CLASS
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(yeah, I know it seems weird in a CS class…)
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Know what work is due, and turn in assignments promptly
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Follow the course’s academic honesty policy
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Be engaged in the learning process, respectful of the course staff, and
supportive of your fellow students
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Express concerns and ask questions
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Understand that the course staff has other obligations outside of this class
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Your Expectations
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The instructor will…
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Tell students what is expected in terms of coursework and behavior
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Be fair in giving assignments, grading assignments, and returning
coursework in a timely fashion
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Let students know how they are doing in the class
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Answer questions and concerns promptly
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Be open to feedback and suggestions
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Be respectful of students
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Try to make the course useful, interesting, and enjoyable
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Understand that students have other obligations outside of this class
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Academic Honesty Policy
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See handout…
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Course Communications
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Email
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Office hours
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One point of EXTRA CREDIT if you come to my office hours (or stop by
any time my door is open) in the next two weeks (i.e., by Thursday 9/13) to
introduce yourself and chat for a few minutes!
Piazza
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Requests for extensions, questions about course policies  Dr. dJ
Grading inquiries, requests for help with assignments  TA
 Still having trouble? Talk to Dr. dJ
Instructor postings and polls
Discussion board
Blackboard
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Some assignment submissions
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CMSC 100 -- Overview
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Homework Expectations
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Homework expectations:
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In general, there will be an assignment (a homework or programming
assignment, or a research paper deliverable) due each Tuesday
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The primary purpose of the homework assignments is to keep you on track
with the reading, and to provide me with feedback about problem areas, well in
advance of the midterm and final exams. (The exams will be very similar to
the homework assignments and will also have some simple programming
questions.)
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Please plan your time (to do the reading and complete the assignments)
accordingly!
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All assignments are to be submitted in class (i.e., as hardcopy!) unless
otherwise specified (and must be legible and stapled!)
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Late policy (see course syllabus)
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CMSC 100 -- Overview
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First Assignments
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IMPORTANT: You need to have access to your own
computer in order to do the work in this class. Please see Dr.
desJardins immediately about access to lab machines if you
do not have your own computer.
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Academic Honesty Policy and Survey: Due Tuesday 9/4
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HW 1: Due Tuesday 9/11
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PA 0: Due Thursday 9/13
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Example: UPC Codes
(ok, ok, so that’s kinda like saying “ATM machines...”)
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Universal Product Codes
Slides for the UPC example courtesy of
Prof. Michael Littman (Brown University)
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First scanned product: Wrigley’s gum (1974)
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Method of identifying products at point of sale
by 11-digit numbers
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Method of encoding digit sequences so they can
be read quickly and easily by a machine
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Reduction Idea
Each level uses an encoding to translate to the next level (i.e., the next
higher abstraction)
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Patterns of ink.
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Sequence of 95 zeros and ones (“bits”).
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Sequence of 12 digits.
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Sequence of 11 digits.
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Name/type/manufacturer of product.
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Product Name
Ponds Dry Skin Cream
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3.9 oz (110g)
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Unilever Home and Personal Care USA
Name Badge Labels (Size 2 3/16" x 3 3/8")
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100 Labels
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Avery Dennison/Avery Division
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11-Digit Number
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Digit = {0,1,2,3,4,5,6,7,8,9}
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Sequence of 11 digits
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QUESTION: How many different items can be encoded?
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Encode Name By 11 Digits
First 6 digits: Manufacturer
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First digit, product category:
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0, 1, 6, 7, 8, or 9: most products
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2: store’s use, for variable-weight items
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3: drugs by National Drug Code number
Last 5 digits: Manufacturer-assigned ID
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Examples
Labels: 0-72782-051440
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0=general product
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72782= Avery
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051440=Avery’s code for this product
Ponds: 3-05210-04300
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3=drug code
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05210= Unilever
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04300=National Drug Code for this product
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12-Digit Number
The UPC folks decided to include another digit for error
checking. Example:
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01660000070 Rose’s Lime Juice (12 oz)
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04660000070 Eckrich Franks, Jumbo (16 oz)
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05660000070 Reese PB/Choc Egg (34 g)
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08660000070 Bumble Bee Salmon (14.75 OZ)
Misread digit #2 and you turn sweet to sour!
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Check Digit
1. Add the digits in the odd-numbered positions (first, third, fifth,
etc.) together and multiply by three
2. Add the digits in the even-numbered positions (second, fourth,
sixth, etc.) to the result
3. Subtract the result from the next-higher multiple of ten. The
result is called the check digit
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Code and Example
01660000070
set evensum to d2+d4+d6+d8+d10
set oddsum to d1+d3+d5+d7+d9+d11
set checkdigit to (0-(3*oddsum+oddsum)) mod 10
01660000070
odd-digit sum: 0+6+0+0+0+0=6
even-digit sum: 1+6+0+0+7=14
odd*3+even = 6*3+14=32
subtract from multiple of 10=40-32=8
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CMSC 100 -- Overview
Lime juice: 01660000070→016600000708
Franks:
04660000070→046600000705
Choc Egg: 05660000070→056600000704
Salmon:
08660000070→086600000701
all are two
digits different
now
Thurs 8/30/12
Some (Mod) Math
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3 x Sodd + Seven = 0 mod 10
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The sum of the odd-position digits (times 3) plus the sum of the
even position digits (including the check digit) is 0 mod 10
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Modulo math is just like regular math, except things wrap
around (like an odometer). Mod 10 means we only pay
attention to the last digit in the number
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Divide by 10 and only keep the remainder
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More Modulo Math
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What’s the check digit for the code 0-000000-000000?
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What happens to the check digit if you add one to an oddposition digit?
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What happens to the check digit if you add one to an evenposition digit?
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Behavior that matters: check digits for “similar codes” (which
might be easily confused/misread) are different (reducing the
probability they’ll be misread)
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Bits
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We’ve gone from a product name to an 11-digit number to
a 12-digit number
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A 0 will appear in the UPC as a white bar (space) and a 1
as a black bar
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So we need to turn each digit (base 10) into a series of bits (base 2)
Also, we want to be sure we alternate 0s and 1s often enough (e.g.,
don’t want 20 black bars (1s) in a row)
Finally, we want to have a code that we can scan in either direction
(i.e., we need to be able to tell which direction we’re reading it in)
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Bits
Digits are encoded as 7-bit patterns
that all:
•start with 0, end with 1
•switch from 0 to 1 twice
•include no pairs of numbers that are
the reverse of each other (“reverse
complements”)
•
0: 0001101
1: 0011001
2: 0010011
3: 0111101
4: 0100011
5: 0110001
6: 0101111
7: 0111011
8: 0110111
9: 0001011
Encode d1 d2 d3 d4 d5 d6 d7 d8 d9 d10 d11 d12 as:
101 d1 d2 d3 d4 d5 d6 01010 d7 d8 d9 d10 d11 d12 101
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CMSC 100 -- Overview
Last 6 digits have 0s and 1s reversed.
(No reverse complements  can tell what
direction we’re scanning in!)
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How Many Bits?
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Question: How many bits (zeros and ones) long is the code for
the original 12-digit sequence?
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Finally, Ink!
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Given the long pattern of bits, we write a 1 as a bar and a zero as a
space
Two 1s in a row become a double-wide bar
Two 0s in a row become a double-wide space
No UPC has more than four 0s or 1s in a row. Question: WHY?
All digits have equal width
All UPCs start and end with bars (actually with black-white-black
pattern)
UPCs can be read upside down
UPCs can be read at an angle or variable speed via ratios
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Example
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.......
Barcode for skin cream:
3-05210-04300-8
(8 is the check digit)
start: 101; 3: 0111101
05210: 0001101-0110001-0010011-0011001-0001101
middle: 01010
04300: 1110010-1011100-1000010-1110010-1110010 (rev)
8: 1001000 (rev); end: 101
The digits underneath are for our benefit (the machine doesn’t read
them!)
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Whew!
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The UPC example illustrates:
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Abstraction
Binary numbers and modulo math
Encoding (error correction, readability
constraints)
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QR Codes
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CMSC 100 -- Overview
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“QR” = “Quick Response Code”

QR codes are kind of like UPC codes...

...but the encoding is a lot more complicated:

Different “versions” provide different resolutions
(which is why the pixels look bigger in some QR
codes than others)

Variable data types and error correction levels

Complex masking scheme enables variable
resolution, etc., but the algorithm to reconstruct the
underlying content is much more sophisticated

No one pixel “means” anything like it does in a
UPC code
Thurs 8/30/12
QR... Coins??

Last year, the Netherlands
introduced the first coins with a
scannable QR code! Wave of the
future... or total gimmick?
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That’s It!
 Any
last questions?
 Enjoy
your long weekend and I’ll see
you on Tuesday!
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