Lecture03

transcript

Knowledge Representationin

Digital HumanitiesAntonio Jiménez Mavillard

Department of Modern Languages and LiteraturesWestern University

Lecture 3

Knowledge Representation in Digital HumanitiesAntonio Jiménez Mavillard

* Contents: 1. Why this lecture? 2. Discussion 3. Chapter 3 4. Assignment 5. Bibliography

Why this lecture?

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

Last assignment discussion

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

Chapter 3

Fundamentals of Programming

1. Designing algorithms2. Elements of a program

Knowledge Representation in Digital HumanitiesAntonio 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?

What is an algorithm?* Exercise 1 (solution) · Recipe:

What is an algorithm?* 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

* Exercise 2 (solution) · 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

* Exercise 2 (solution) · How many times is 3 contained in 7?

* Exercise 2 (solution) · Count the number of sustractions

What is an algorithm?* Exercise 2 (solution)

What is an algorithm?* Exercise 2 (solution) Is the algorithm correct? Trace for 7/3

Step 0 A is 7, B is 3, C is 0Step 1 Is 7 >= 3? Yes A is now 7 3 = 4 C is now 0 + 1 = 1Step 2 Is 4 >= 3? Yes A is now 4 3 = 1 C is now 1 + 1 = 2Step 3 Is 1 >= 3? NoStep 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

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

Components of a program* 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 = 0index = 0while index < len(fruit): char = fruit[index] if char == 'a': counter += 1 index += 1print counter

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

* Exercise 3 (solution) · 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

Components of a program* Exercise 3 (solution) · 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'sKnowledge Representation in Digital Humanities

Antonio Jiménez Mavillard50

fruit = 'banana'counter = 0index = 0while index < len(fruit): char = fruit[index] if char == 'a': counter += 1 index += 1print 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.

BibliographyCormen, 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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