Abstraction

What is abstraction?

Starter

Use the cards that you have been given and see if you can do this trick. I will explain how it works in the plenary.



We will use abstraction to work out how it is done.

First activity

Tourist map

This is going to sound strange but it is a Computer Science task. Construct a tourist map of Whittlesey.

First look at a map of Whittlesey on Google below and draw a rough tourist map on a piece of plain paper. You have 5 minutes only but you must be as accurate as you can. You are trying to make a map that would be useful for a tourist as well as easy to read and see the key landmarks and features of Whittlesey. Timer

 

Outcome

You will not have had time to get everything in; so, what have you missed out?

Significance

This is abstraction. Leaving out the unimportant and including only the important.

Write down on your drawing everything of importance that you included in your drawing. Now write down what you missed out.

Here is a famous abstraction.

What are the similarities with your tourist map?

Snakes and ladders

Ignore the unimportant

Think "Computationally" about the game

Case

Just imagine that you are to write a program in Python to play snakes and ladders; what do you need to know?

In essence you are to make an abstraction of snakes and ladders; what is in and what is not?

Discussion

What did you decide? Do you need to know the length of a snake? Are snakes different from ladders? Can we ignore the colours? Does anyone know what sort of programming uses a model (an abstraction) in this way?

Significance

The abstraction (if created accurately and thoughtfully) leads to the system requirement which in many systems is the most crucial part of the process. I recently met (at a rather nice dinner) a chap in the aerospace industry who said that the requirement was 50% of the process and testing the requirement another 40% leaving 10% for everything else. (Incidentally if you are interested they simply cannot recruit new engineers £30k to start and £80k for a senior engineer.)

Another magic trick

Watch the hands

Watch the trick carefully; can you work out how it was done. The hint here is that this is another view of abstraction in action.



How do you think that it was done? Discuss.

Case

The magician deliberately confuses the audience by adding a significant quaintly of obfuscation, camouflage, extra movement and patter. All of this is done to hide the actual mechanics of the trick. The hand is not quicker than the eye, simply we are not trained to know what to look for.

Outcome

Do you now see how the trick was done? Might you want to try it at home?

Make a list in two columns of the abstraction and obfuscation. Which list is longer?

Plenary

so, how was it done?

Solution

Think about the position of the cards in the deck.

The target card is at the bottom of the chosen pile and that pile is picked first and all of the other cards placed beneath to the target is always in position 3.

When the cards are dealt to spell the number of the card the target is dealt third. All of the numbers are at least three characters long, so the card stays in position three from the end - position seven.

The dealer deals two cards off the top for of and places the remainder including the target on top. The target is now in position five.

The dealer deals the cards for the name of the suit; this is always 5 characters or greater so the target stays at position five.

Finally the word M A G I C and the target pops up with the C.

Simples!

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