Ch. 1
Ch. 2

# Lesson 8: Create a Representation

## Overview

In this lesson students design a structure to represent their perfect day using the binary representation systems they've learned in this chapter. Students will first write a short description of their perfect day and then review with a partner to identify the key pieces of information they think a computer could capture. As a class students will decide how a punch card of bytes of information will be interpreted to represent those pieces of information. Students will then use the ASCII, binary number, and image formats they have learned to represent their perfect days. Students then trade punch cards and try to decipher what the other student's perfect day is like. The lesson ends with a reflection.

## Purpose

This lesson forces students to grapple with some of the challenges of representing information to a computer. Computers are good at representing some kinds of information like numbers or characters, but this forces people to represent information in ways that might not always capture the full analog experience of an object or event. The project also serves as a cumulative project for the chapter, bringing together the different representation systems students have learned. As students move into the next chapter they'll look more closely at how information is used to make decisions once it's in a format that can be input to a computer.

## Objectives

### Students will be able to:

• Choose and justify the use of different binary representation systems depending on the information being represented
• Encode and decode information represented in binary numbers and ASCII text
• Create a generalized representation system for many instances of a complex type of information

Heads Up! Please make a copy of any documents you plan to share with students.

# Teaching Guide

## Warm Up (5 mins)

Teaching Tip

Jump to the Project: Assess for yourself, based on students' understanding of the previous lesson, if you think these points from the previous lesson need to be reviewed. If not then just jump into the project.

Review: You may wish to begin this lesson with a quick review of the representation systems students have learned in this chapter. You may wish to point on in particular that a byte of information (8 bits) on has meaning if you know

1. The system that is being used.
2. The meaning of the information itself.

Without 1. you could not distinguish a number from a character from a line in an image. Even if you know what the information is (e.g. the number 8) you don't know necessarily if that number means a shoe size, an age, or a movie rating. These should be points that you can make based on the previous lesson.

## Activity (40 mins)

Group: Students will need to work collaboratively on this project

Distribute: Give students copies of the Project Guide

#### Project Guide - Create a Representation

Prompt: Close your eyes and think about your perfect day. What is the weather like? What will you do? Who's there with you? Spend a minute thinking about as many details as you can.

Step 1 - Describe Your Perfect Day: Have students write down all the key details of their perfect day on their activity guides. It is fine for students to mix between bullets and complete sentences.

Step 2 - Share with a Partner: Have students pick a neighbor to share their perfect day with. They should continue to update their information from Step 1 as they come up with more information about their perfect day.

Teaching Tip

Choosing Categories: This will likely prove a difficult step for some students. You may wish to model how to assign different information to different categories or as a class assign information from a few volunteers' perfect days.

Step 3 - Identify Information: Have students assign the information about their perfect day to one of three categories, Numbers, Characters, or Images.

Step 4 - Review Information Choices: Students should get back together with their partner and compare notes on how they assigned different pieces of information to different categories.

Discussion Goal

Possible Systems: Here's one possible system for the punch cards

• Number 1: Temperature that day
• Number 2: How many other people are there
• Number 3: How long you're there in hours
• Characters 1-10: Name of activity or location
• Image: Image of the activity

Facilitating the Discussion: Students will likely want to create systems that work really well for their information but not a classmates. Emphasize that systems are only useful if they're universal. A system that only works for one person isn't very useful and all systems will involve some tradeoffs.

Step 5 - Full Class Activity - Agree on Classwide Punch Card: Display the punch card from the project guide somewhere the whole class can see it. Have partners share the categories of information they wish to represent. Explain that the class will need to agree how they are going to use each row from the numbers, characters, and image sections of the punch card.

Step 6 - Fill Out Punch Card: Display the system somewhere all students can see it. Have students fill out their punch cards using this class system.

Step 7 - Trade and Decode Punch Cards: Students should find a new partner who is unfamiliar with their perfect day. They should trade punch cards and decode the information encoded their. There is space on the back of the activity guide to write

• The number information and its meaning
• The character information and its meaning
• What they believe the image is showing

Afterwards students should write what they believe happens in their classmate's perfect day in the space provided

Step 8 - Share and Reflect: Partners should meet back up and compare their description of their classmate's perfect day to what they originally intended. what were they still able to capture? What was lost?

## Wrap Up (10 mins)

Discussion Goal

Goal: These questions should help you assess on a high level whether students have understood the challenges of this activity. In their justifications for the first question they should be describing what information they'd want to capture and how they'd want to represent it. In the second question you should push them on why it's ok to lose the byte from one category and why that loss of information will be made up for by the new byte in another category.

Collect: Students' project guides and punch cards. Make sure to keep track of who students have partnered with so that you can grade both their encoding and decoding work.

Prompt: If you wish you may use the following prompts to debrief the project.

• If you had been given another byte of information (another line on the punch card) how would you have wanted to use it?
• If you could move one byte from one category (numbers, images, characters) to another, which would you switch?

Discuss: Have students silently write their ideas before sharing with a partner and eventually the whole class.

Send students to Code Studio to complete their reflection on their attitudes toward computer science. Although their answers are anonymous, the aggregated data will be available to you once at least five students have completed the survey.

• Reflection
• 2
• (click tabs to see student view)
View on Code Studio

## Standards Alignment

#### CSTA K-12 Computer Science Standards (2017)

AP - Algorithms & Programming
• 2-AP-10 - Use flowcharts and/or pseudocode to address complex problems as algorithms.
• 2-AP-13 - Decompose problems and subproblems into parts to facilitate the design, implementation, and review of programs.
DA - Data & Analysis
• 2-DA-07 - Represent data using multiple encoding schemes.