Lecture03

Knowledge Representation
in
Digital Humanities
Antonio Jiménez Mavillard
Department of Modern Languages and Literatures
Western University

Lecture 3
Knowledge Representation in Digital Humanities
* Contents:
1. Why this lecture?
2. Discussion
3. Chapter 3
4. Assignment
5. Bibliography
2

Why this lecture?
* This lecture...
· trains the problem solving skill by means
of algorithm formalization
· prepares the ground to write real
programs
3

Last assignment discussion
* Time to...
· consolidate ideas and
concepts dealt in the readings
· discuss issues arised in the specific
solutions to the projects
4

Chapter 3
Fundamentals of Programming
1. Designing algorithms
2. Elements of a program
Antonio Jiménez Mavillard5

Chapter 3
1 Designing algorithms
1.1 The programming process
1.2 What is an algorithm?

Chapter 3
2 Elements of a program
2.1 What is a program?
2.2 Components of a program
2.3 Types of errors

Designing algorithms

The programming process
* Programming cycle:
1. Define the problem
2. Plan the solution
3. Code the program
4. Test the program
5. Document the process

* Define the problem
· Identify the input data
(what we have)
· Determine the output information
(what we want to obtain)

* Plan the solution
· Design an algorithm
+ by drawing a flow diagram
+ by writing pseudocode

* Code the program
· Translate the algorithm into a
programming language

* Test the program
· Verify if for certain input, the program
produces the correct output
· Find and fix errors (debugging):
+ syntax
+ runtime
+ semantic

* Document the process
· Describe the problem and the solution
· Include pseudocode or flow diagrams
· Report testing results
· Comment the code

References
Glassborow, Francis. “Chapter 1: You Can Program.” You Can Do It!: A Beginner’s Introduction to Computer
Programming. Chichester, West Sussex, England; Hoboken, NJ: John Wiley, 2004. Print.
Mohd Harris. “PROG0101 - Fundamentals of Programming.” N. p., n.d. Web. 17 Jan. 2014.
Perry, Greg M. “Chapter 2: Anatomy of a Program.” Absolute Beginner’s Guide to Programming. Indianapolis, Ind.: Que
Pub., 2003. Print.

What is an algorithm?
* Definitions
· A detailed plan to solve a problem
· A step-by-step set of instructions for
solving a problem
· A finite process that if followed will
solve a problem

* Characterized by 5 properties:
1. Input: initial data
2. Output: final result

* Characterized by 5 properties:
3. Finiteness: has to terminate in a finite
number of steps
4. Definiteness: each step has to be
unambiguously specified
5. Effectiveness: each step should be
doable in a finite time by a human

* Exercise 1
· A recipe is an algorithm that solve the
next problem: how to prepare a meal
· Search for the recipe of Green Tea
Berry Delight
(http://allrecipes.com/Recipe/Green-Tea-Berry-Delight/Detail.aspx)

* Exercise 1
· Identify: input, output and steps
· Answer the following questions:
+ Is the recipe finite?
+ Is each step definite?
+ Is each step effective?

* Exercise 1
(solution)
· Recipe:

* Exercise 1 (solution)
· Is the recipe finite?
Yes, it is done in 5 minutes
· Is each step definite?
Yes, they are not ambiguous
· Is each step effective?
Yes, in fact they are thought to be
done by a human

* Exercise 2
· Design an algorithm to divide two
numbers by using only additions and
substractions

· Solve the specific case: divide 7 by 3
Hint: how many times is 3 contained in 7?
· Solve the general case: divide A by B

· How many times is 3 contained in 7?

· Count the number of sustractions

* Exercise 2
(solution)

* Exercise 2
(solution)
Is the
algorithm
correct?
Trace for
7/3
Step 0
  A is 7, B is 3, C is 0
Step 1
  Is 7 >= 3? Yes
    A is now 7 3 = 4
    C is now 0 + 1 = 1
Step 2
  Is 4 >= 3? Yes
    A is now 4 3 = 1
    C is now 1 + 1 = 2
Step 3
  Is 1 >= 3? No
Step 4
  Output C, that is 2

References
Cormen, Thomas H. “Chapter 1: The Role of Algorithms in Computing.” Introduction to Algorithms. Cambridge,
Masachusetts; London: The MIT Press, 2009. Print.
De la Rosa, Javier. “Computer Tools for Linguists.” Yutzu. N. p., n.d. Web. 16 Sept. 2013.
Knuth, Donald E. “Chapter 1: Basic Concepts.” The Art of Computer Programming. Volume 1: Fundamental Algorithms.
Vol. 1. Reading, Mass.: Addison-Wesley, 1997. Print.

Elements of a program

What is a program?
* Definition
“A program is an implementation of an
algorithm in a program language.”
(The concrete written program is called
source code or just code)

What is a program?
* Algorithm vs program
· Algorithm:
+ Abstract
+ Represented by a flow diagram,
pseudocode...
+ For human understanding

What is a program?
* Algorithm vs program
· Program:
+ Concrete
+ Represented by a program language
+ For computer processing

Components of a program
* The content and structure of a program
depend on the programming language
* Every programming language is formed by
a set of symbols
* The combination of these symbols defines
the programs

* Programming languages are defined by:
· Morphology
· Syntax
· Semantics

* Morphology
· Symbols: numbers, letters and special
characters
· Symbols are combined to form tokens:
the basic elements of a language

* Morphology
· Vocabulary: a set of keywords (special
tokens) with specific funcionality
· Examples in Python:
def, elif, except, print

* Syntax
· Grammar rules to write a program
+ Tokens
- How the symbols are combined
- Examples in Python:
correct: 3, counter, def
incorrect: $+1, (&variable

* Syntax
· Grammar rules to write a program
+ Structure
- Way that tokens are arranged
- Expressions, blocks...
- Examples in Python
correct: a += 1
incorrect: a $= 1

* Semantics
· Meaning of the program
· Examples: how to interpret the order of
the operators
+ Operator precedence
x - 2 * 3 ≡ x - (2 * 3)
+ Operator associativity
x - 2 + 3 ≡ (x - 2) + 3

* A program is a set of instructions
* An instruction is an statement
* A statement is an executable unit of code
formed by expressions
* An expression is a combination of tokens
* A token is a sequence of symbols

* Exercise 3
Given the next code...
fruit = 'banana'
counter = 0
index = 0
while index < len(fruit):
    char = fruit[index]
    if char == 'a':
        counter += 1
    index += 1
print counter

* Exercise 3
... identify:
· Symbols, tokens and keywords
· Some grammar rules
· Its semantics

· symbols: letters, numbers, ', <, (, ), :,
=, [, ], and +
· tokens: fruit, =, 'banana', counter, 0,
index, while, <, len(fruit), :, char,
fruit[index], if, ==, 'a', +=, 1, print
· keywords: while, len, if, print

· grammar rules: quotations for strings '',
colon after testings :, indentention for
blocks, closing parenthesis after opening
parenthesis (), closing bracket after
opening bracket []
· semantics: counts and print on screen
number of a's in the word “banana”

References
The Little Introduction To Programming. N. p. Web.

Types of errors
* Syntax error
The code of the program breaks the
syntax rules of the programming language
* Logic error
The code is syntactically correct but
results in illegal operations in execution
* Semantic error
The program does not behave as expected

Types of errors
* Examples in Python
· Syntax error
a + 1 = b Assignment malformed
· Logic error
a = 4
b = 0
c = a / b
Division by 0
my_list = [1, 2, 3, 4]
element = my_list[7]
Access to a non
existing object

Types of errors
* Examples in Python
· Semantic error
It does not print the number of a's
fruit = 'banana'
counter = 0
index = 0
while index < len(fruit):
    char = fruit[index]
    if char == 'a':
        counter += 1
    index += 1
print fruit

References
Severance, Dr Charles R. “Chapter 1: Why Should You Learn to Write Programs?” Python for Informatics: Exploring
Information. 1 edition. CreateSpace Independent Publishing Platform, 2013. Print.

Assignment
* Assignment 3: Playing with algorithms
· Readings
+ The Role of Algorithms in Computing
(Introduction to Algorithms)
+ Strings (Python for Informatics)

Assignment
* Assignment 3: Playing with algorithms
· Project
+ Write an algorithm in Python that
cleans a text of punctuations marks
O Romeo Romeo wherefore
art thou Romeo Deny thy
father and refuse thy
name Or if thou wilt not
be but sworn my love And
I'll no longer be a
Capulet
O Romeo, Romeo! wherefore
art thou Romeo? Deny thy
father and refuse thy
name; Or, if thou wilt
not, be but sworn my
love, And I'll no longer
be a Capulet.
»

References
Cormen, Thomas H. “Chapter 1: The Role of Algorithms in Computing.” Introduction to Algorithms. Cambridge,
Masachusetts; London: The MIT Press, 2009. Print.
Severance, Dr Charles R. “Chapter 6: Strings” Python for Informatics: Exploring Information. 1 edition. CreateSpace
Independent Publishing Platform, 2013. Print.

Bibliography
Cormen, Thomas H. Introduction to Algorithms. Cambridge, Masachusetts; London: The MIT Press, 2009. Print.
Glassborow, Francis. You Can Do It!: A Beginner’s Introduction to Computer Programming. Chichester, West Sussex,
England; Hoboken, NJ: John Wiley, 2004. Print.
Knuth, Donald E. The Art of Computer Programming. Volume 1: Fundamental Algorithms. Vol. 1. Reading, Mass.:
Addison-Wesley, 1997. Print.
Mohd Harris. “PROG0101 - Fundamentals of Programming.” N. p., n.d. Web. 17 Jan. 2014.
Perry, Greg M. Absolute Beginner’s Guide to Programming. Indianapolis, Ind.: Que Pub., 2003. Print.
Severance, Dr Charles R. Python for Informatics: Exploring Information. 1 edition. CreateSpace Independent Publishing
Platform, 2013. Print.
The Little Introduction To Programming. N. p. Print.

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