Courses/Computer Science/CPSC 203/CPSC 203 2007Fall L04/CPSC 203 2007Fall L04 Lectures/Lecture 4

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Lecture 4

We finish the "Only Connect" lecture on the large-scale structure of the Internet, sharpen the "dots" and "edges" visual tools we have been using to model the Internet, and introduce the notion of "Information" visually.

The objectives of today's class are:

  • House Keeping
    • Pick a mid-term date (either Oct 23rd (Tuesday) or Oct 25th (Thursday)
    • Quick look at some of the Term Project initial statements
  • "Only Connect" finale
    • Internet Physical Structure: Tier 1, Tier 2, Tier 3 Internet service providers.
    • New glossary on "Dots" and "edges" and Information.
    • Dots and Edges
    • Information (in terms of Dots and Edges)

Lecture Glossary

  • Tier1 --- Tier3 Internet service providers
  • Dot ---> "Node", "Vertice"
  • Edge ---> "Relation", "Connection", "Arc", "Information flow".
    • Directed Edge
    • Undirected Edge
  • Paths and Cycles
  • Connected/Disconnected
  • Model
  • Information
    • Information Capacity
    • Information Constraint
    • Information Flow

Dots and Edges

... where various Dots and Edges are drawn on the overhead and blackboard .... you are getting this down aren't you. We introduce dots and edges as a modelling approach, relate it to future items we learn in this course, and use it as a way of visualizing information concepts.


Gregory Bateson, a biologist and systems thinker defined Information as "The Difference that makes a Difference". See:

From that site:

"Bateson defines information as "a difference that makes a difference".

Hold your hand perfectly still, palm upwards and resting comfortably on a table. With your other hand, drop a small coin into the palm. You will feel the impact, and if the coin is cold, you will feel the coldness of the metal. Soon however, you will feel nothing. The nerve cells don't bother repeating themselves. They will only report to the brain when something changes. Information is difference.

A lizard hunting insects operates on the same principle. The lizard's eye only reports movement to the lizard's brain. If the hunted insect settles on a leaf, the lizard literally cannot see it. But the moment the insect starts to move, whop, the lizard can see it again, and the tongue flickers out and catches it.

But there are differences and differences. Information is difference that makes a difference. You were probably aware, as you dropped the coin into your palm, your eyes told you automatically, without your brain even asking, what the value of the coin was; but you were probably not aware what date it was minted. This is because (unless you are a numismatist) the value of the coin makes a difference to you whereas its date doesn't.

What is it that makes a difference to a lizard, to a numismatist, to you? Surely not the same things. What is information for the lizard is not information for you, and what is information for you is not information for the lizard.

This is why the perspective of information is important. Perspective defines what counts as information at all, perspective defines to whom the information makes a difference. "

Wikipedia, (see "information Basics" under Resources) takes a more IT oriented approach to information as:

Information is the result of processing, gathering, manipulating and organizing data in a way that adds to the knowledge of the receiver. In other words, it is the context in which data is taken.

Information as a concept bears a diversity of meanings, from everyday usage to technical settings. Generally speaking, the concept of information is closely related to notions of constraint, communication, control, data, form, instruction, knowledge, meaning, mental stimulus, pattern, perception, and representation.

I will take a very "visual" approach to information and define it in terms of Information Capacity, Information Constraint, and Information Flow in a model of a system using Dots and Edges.

At the end, we will return to the Tier1 ... Tier3 Internet design, and discuss it using our new concepts of Information.

Only Connect : Origins and Structure of the Internet

Only connect! That was the whole of her sermon.

Only connect the prose and the passion, and both will be exalted,

And human love will be seen at its height.

Livfe in fragments no longer.

Only connect ...

-- E.M. Forster, Howards End.


  • TIA 4th Edn: Chapter 13, pp 572-578
  • TIA 3rd Edn: Chapter 13, pp 546-552


  • "Introduction to Graph Theory" By Richard J. Trudeau. Dover Press, 1993. Originally called, "Dots and Edges" -- if you find playing with dots and edges fun, and want to learn more --- this is the place to start. You can usually find a copy at a used bookstore's math section for < $10