CS 150: Computing from Ada to the Web

The Philosophy of Programming

Liberal Arts Recap

• Language/Literature– Grammars and defining languages– Recursion in literature

• Visual Arts– Recursion in Escher’s drawings– Fractals

• Music– Bach’s Canons– Foo Fighters’ in recursion

Philosophy

• Definition: “Philosophy is the discipline concerned with questions of how one should live (ethics); what sorts of things exist and what are their essential natures (metaphysics); what counts as genuine knowledge (epistemology); and what are the correct principles of reasoning (logic).”

How does Philosophy relate to CS?

• A more general definition: “How we view the world.”

• How do we represent the world around us?• How do we turn what we see into the world

into something digital? Something a computer can understand and operate on?

Topics we’ll cover in Philosophy

• Modeling the world– Object-oriented programming– Abstract Data Types– Data modeling

• Inheritance– How objects relate to each other

• Requirements and Design– Understanding the needs of others

• Ethics in Computer Science

What have we been programming

• Functional Programming Paradigm– “treats computation as the evaluation of

mathematical functions and avoids state and mutable data. It emphasizes the application of functions, in contrast with the imperative programming style that emphasizes changes in state.”

How do we view the world?

• Some take the world and can turn it into mathematical functions…– Mathematicians– Physicists

• How do you view the world?

How I (Mark Sherriff) View the World

• Millions of interconnected and interrelated objects– Example: this classroom• The room sits in a particular spot in a particular building

at a particular place on grounds.• Inside the room is a set number of seats is a prescribed

formation• In some of the seats are students

Object vs. Instance

• What is an object?– Is it a thing? Is it a place? Is it a person?

• An object has attributes– Where is the object?– What is the object like?

• An object has functions– What can the object do?– What is it used for?

Object vs. Instance

• An instance is a particular object– I (Mark) am an instance of a professor– My Civic is an instance of the general object car

• What instances are there in this room?• What differentiates one instance from

another?

Another way to say it

• Entity vs. Entity Set– An entity set is the general category that an object

comes from (i.e. desks)– A particular entity is a specific object from the set

(i.e. the desk at the very front on the right)

The Philosophy of OO

• Why does the way we view the world matter?• How does a computer “view the world?”– What is machine language like?– Can we read/understand machine language?

• The programs we have written so far are nice, but are they things you’d use in your everyday life?

• What are programs you use every day?

List of programs

• Internet Browsing: Firefox, Safari, Opera• Email: Thunderbird, GMail, Webmail• Calendar: iCal, GCal• Music: iTunes, Rhapsody, Napster, … others• Games: Solitare, Wii, XB360, DS• IM: AIM, Adium• Office: MS Office, iWork, OpenOffice

What are the purposes of these programs?

• Solve real-world problems• Provide real-world solutions• Improve quality of life

• So, how do you represent all that in 1’s and 0’s?

The world you are trying to model• How do you tell a computer what any of this stuff

is?• Each programming paradigm has a different

“language” it speaks to model the world• Functional programming models the world in the

terms of mathematics.• OO programming models the world by saying

that everything is an object unto itself, with attributes and functions that it can carry out, affecting other objects.

Finding Objects

• Define the object Book.

Finding Objects

• Define the object Book.• A book has:– A title– An author– A publisher– Copyright– Pages of text– Pages with pictures

Finding Objects

• Well… what’s a page?– A page is a single sheet of paper that has text on

it.

• Well… what’s paper?• How far down do we need to go?• Remember: What is the world you are trying

to model?

Finding Objects

• Consider a library• Now, what do you need to know about a

book?

How do we represent objects in code

• Classes– Classes are made up of primitive types and

functions.– Classes are entity sets / objects because they

define an entire category of objects– Classes can be instantiated, creating instances– An instance is a particular entity from the class• i.e. the front right desk is an instance of the Desk class

The building blocks of a class

• Attributes– Pieces of data that define the object

• Functions / Methods– Functionality that the object has– Functionality that can be performed on the object

Class in PHP<?php

class Book { var $title; var $author; var $publisher; var $pages; var $callNumber;

}

?>