GCE AS/A LEVEL
WJEC GCE AS/A LEVEL in
COMPUTER SCIENCE
ACCREDITED BY WELSH GOVERNMENT
This Welsh Government regulated qualification is not available to centres in England.
Teaching from 2015
TEACHERS’ GUIDE
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Guidelines and tips
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Community
Ask the community
Ask the community for help and clear up your study doubts
University Rankings
Discover the best universities in your country according to Docsity users
Free resources
Our save-the-student-ebooks!
Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors
COMPUTER SCIENCE TEACHERS' GUIDE, Study notes of Computer Science
A level Computer Science specification and to offer guidance on the requirements of the qualification and the assessment process.
Typology: Study notes
2021/2022
1 / 30
This page cannot be seen from the preview
Don't miss anything!
Related documents
Partial preview of the text
Download COMPUTER SCIENCE TEACHERS' GUIDE and more Study notes Computer Science in PDF only on Docsity!
GCE AS/A LEVEL
WJEC GCE AS/A LEVEL in
COMPUTER SCIENCE
ACCREDITED BY WELSH GOVERNMENT
This Welsh Government regulated qualification is not available to centres in England.
Teaching from 2015
TEACHERS’ GUIDE
INTRODUCTION
The WJEC AS and A level Computer Science qualifications, accredited by Welsh Government for first teaching from September 2015, are available to:
- All schools and colleges in Wales
- Schools and colleges in independent regions such as Northern Ireland, Isle of Man and the Channel Islands The AS will be awarded for the first time in Summer 2016, using grades A‒E; the A level will be awarded for the first time in Summer 2017, using grades A*‒E.
The qualifications have been developed following detailed consultation with experienced examiners, teaching practitioners and with Higher Education. They offer a contemporary approach to the subject from both theoretical and practical perspectives. They encourage students to apply the fundamental principles and concepts of computer science to a wide range of situations by offering a broad course of study that allows students the opportunity to analyse problems and to solve these problems using computational thinking. Students are encouraged to think creatively and innovatively in producing their solutions to problems and to consider relationships between different aspects of computer science as well as the impact of computer science on today’s global society.
An emphasis on programming, mathematics and algorithms underpins each unit, mirroring the ubiquity of programming in computer science and encouraging learners to think like programmers.
Units 1, 2, 3 and 4 of the qualification encourage candidates to study a wide range of concepts and principles of computer science and are assessed by internal examination, with Unit 2 being on-screen examination. Unit 5 encourages candidates to utilise their theoretical knowledge in a practical context by programming a solution to a problem.
The WJEC AS and A level Computer Science qualifications have been designed to give a broad scope of study opportunities that prepare candidates for Higher Education or employment in a computer- related field. Equally, they are relevant to students who continue their studies in an unrelated field, given the widespread nature of computer science all areas of today’s society.
These qualifications have been designed to free centres to concentrate on innovative delivery of the course by having a streamlined, uncomplicated, future-proof structure, with realistic technological requirements.
Additional ways that WJEC can offer support :
- Specimen assessment materials
- Face-to-face CPD events
- Examiners' reports on each question paper
- Free access to past question papers and mark schemes via the secure website
- Direct access to the subject officer
- Free online resources
- Exam Results Analysis
- Online Examination Review
AIMS OF THE TEACHERS’ GUIDE
The principal aim of the Teachers’ Guide is to support teachers in the delivery of the new WJEC A level Computer Science specification and to offer guidance on the requirements of the qualification and the assessment process. The guide is not intended as a comprehensive reference , but as support for professional teachers to develop stimulating and exciting courses tailored to the needs and skills of their own students in their particular institutions.
The guide offers assistance to teachers, suggesting possible classroom activities and links to digital resources (both our own, freely available, digital materials and some from external sources) to provide ideas for immersive and engaging lessons. The guide will concentrate on those areas new to WJEC subject specifications and those subject areas where guidance has been requested most.
ASSESSMENT STRATEGY : KEY EXAMINATION COMMAND WORDS (2 OF 2)
ASSESSMENT OBJECTIVES AND THEIR RELATED COMMAND WORDS
Assessment Objective Description Command words Example questions
AO3 Design, program and evaluate
computer systems that solve problems,
making reasoned judgements about
these and presenting conclusions
Assess Evaluate Write algorithms Write a command Debug Correct Examine Determine
Evaluate the efficiency of the algorithm and, using Big O notation, determine the growth rate for the time performance. Your answer should refer to the addition and multiplication calculations performed by the algorithm. [5]
Write an algorithm fragment which is suitable for parallel processing. To gain both marks, your fragment should demonstrate at least three calculations which can be carried out in parallel. [2]
Write an SQL command to output the names of students who have the tutor with number 378. [1]
KEY ASPECTS OF THE SPECIFICATION FROM 2015
UNIT 1: FUNDAMENTALS OF COMPUTER SCIENCE
AREA OF STUDY DESCRIPTION
Parallelisation (^) Explain parallel processing.
Logical Operations Draw truth tables for Boolean expressions consisting of AND, OR, NOT and XOR, logical operations and apply them to combinations of conditions in programs.
Simplifying Boolean Expressions
Show how to simplify Boolean expressions using Boolean identities and rules.
The Von Neumann Architecture and Fetch- Execute Cycle
Describe the fetch-execute cycle in terms of the flow of processes through a computer (specifically Von Neumann architecture).
Sign and Magnitude and Two’s Complement
Represent positive and negative numbers using both sign/magnitude and two's complement notation.
UNIT 3: PROGRAMMING AND SYSTEM DEVELOPMENT
AREA OF STUDY DESCRIPTION
Binary Trees Describe, interpret and manipulate binary trees and represent their operation by using pointers and arrays.
Linked Lists Describe, interpret and manipulate linked lists and represent their operation by using pointers and arrays.
Hash Tables Describe, hash tables and justify their use in given situations.
Logical Operations Draw truth tables for Boolean expressions consisting of AND, OR, NOT, XOR, NAND and NOR logical operations and apply them to combinations of conditions in programs.
Simplifying Boolean Expressions
Show how to simplify Boolean expressions using Boolean identities,rules and De Morgan’s laws
Big O Notation Use Big O notation to determine the efficiency of different sorting algorithms in terms of their time and space requirements and to compare the efficiency of different sorting and searching algorithms. Use this notation to determine the complexity and efficiency of given algorithms in terms of their execution time, their memory requirements and of different algorithms that perform the same task
Shortest-Path Algorithms (^) Explain and apply a shortest-path algorithm (e.g. Dijkstra's algorithm).
Backus-Naur Form Express language syntax using Backus-Naur form.
Waterfall and Agile Describe the different approaches to the analysis and design of programs that Waterfall and Agile methodologies bring.
UNIT: 1 AND 4 EXAM LEVEL: AS/A
AREA OF STUDY
Parallelisation
Key Points:
- Learners should understand that parallel processing is a form of computation in which many calculations are carried out simultaneously, operating on the principle that large problems can often be divided into smaller ones which are then solved concurrently.
- Questions on parallel processing will relate to AO1 and AO2.
Provides an opportunity to develop the following skills: Speaking, Listening and understanding; Reading; Writing; Understanding numerical data; Carrying out calculations; Interpreting results; Presenting findings; Using ICT systems; Finding, selecting and exchanging information; Improving own learning and performance; Developing and presenting information using ICT; Working with others- plan do and review.
INSPIRATION FOR TEACHING
Example
Activity Name : Four Heads better Than One?
- Ask the class for five volunteers to help you demonstrate the advantages of parallel processing.
- Explain to the class that the task of sorting a deck of playing cards by suit (Clubs, Diamonds, Hearts and Spades), and in ascending order (from Ace to King) can be completed much quicker by four people (a Quad-core processor) than by one person (a Single-core processor).
- Shuffle two decks of cards, hand one deck to the lone learner and give a quarter of the other deck to each of the learners in the group of four. The task is to sort both decks of cards as quickly as possible.
- Ask the class to investigate situations where parallelisation is not always quicker than a single-core processor.
- You could ask learners to research Amdahl's law: 𝑇𝑇(𝑛𝑛) = 𝑇𝑇( 1 )(𝐵𝐵 + (^) 𝑛𝑛^1 ( 1 − 𝐵𝐵))
ADDITIONAL RESOURCES
WJEC > A Level Computer Science > Specification from 2015
WJEC > A Level Computer Science > Specimen Assessment Materials
UNITS: 1 AND 3 EXAM LEVEL: AS/A
AREA OF STUDY
Logical Operations
Key Points:
- Learners should understand that logical operators establish relationships between statements that can be either TRUE or FALSE.
- There are six logical operators that students are required to know; AND, OR, NOT, XOR, NAND and NOR.
- Questions on logical operators will relate to AO1 or AO2.
Provides an opportunity to develop the following skills: Speaking, Listening and understanding; Reading; Writing; Understanding numerical data; Carrying out calculations; Interpreting results; Presenting findings; Using ICT systems; Finding, selecting and exchanging information; Improving own learning and performance; Developing and presenting information using ICT; Working with others- plan do and review.
INSPIRATION FOR TEACHING
Example
Activity Name : Put Your Hands Up If…
- Tell learners that they are going to help demonstrate the meaning of each of the logical operators AND, OR and NOT.
- Ask all the students wearing blue to raise their hands and count the number of hands raised. Then ask all the students who are wearing blue AND a watch to keep their hands in the air, ewer hands should be raised. Explain that using the AND operator has narrowed the results.
- Ask all the learners wearing blue OR a watch to raise their hands, more hands should be raised. Explain that using the OR operator has expanded the results.
- Explain that logical operators can be used in combination. For example, ask all the students who are NOT wearing a watch AND have brown hair OR are wearing earrings to raise their hands.
- Explain that a raised hand can be represented as being TRUE or '1' and a lowered hand as FALSE or '0' and so be used to represent each operator in a truth table.
ADDITIONAL RESOURCES
WJEC > A Level Computer Science > Specification from 2015
WJEC > A Level Computer Science > Specimen Assessment Materials
UNITS: 1 AND 3 EXAM LEVEL: AS/A
EXAMPLE BOOLEAN IDENTITIIES
Apply the following Boolean identities to real-life situations:
i) 1 + A = 1
ii) 0 + A = A
iii) A + A = A
iv) 0. A = 0
v) 1.A = A
vi) A + B = B + A
Apply the following Boolean identities where A is " It's raining " and B is " I have an umbrella ".
i) A****. B = B****. A
ii) A + ( A****. B ) = A
iii) A .( A+B) = A
ADDITIONAL RESOURCES
WJEC > A Level Computer Science > Specification from 2015
WJEC > A Level Computer Science > Specimen Assessment Materials
UNIT: 1 EXAM LEVEL: AS/A
AREA OF STUDY
The Von Neumann Architecture and Fetch-Execute Cycle
Key Points:
- Learners should be able to identify and describe the main components of Von Neumann computer architectures.
- Learners should be able to describe the fetch-execute cycle, including how data can be read from RAM into registers.
- Questions on the Von Neumann architecture and the fetch-execute cycle will relate primarily to AO1.
Provides an opportunity to develop the following skills:
Speaking, Listening and understanding; Reading; Writing; Understanding numerical data; Carrying out calculations; Interpreting results; Presenting findings; Using ICT systems; Finding, selecting and exchanging information; Improving own learning and performance; Developing and presenting information using ICT; Working with others- plan do and review.
INSPIRATION FOR TEACHING
Example
Activity Name : The Class as a Fetch-Execute Cycle
- Select the image (left) for detailed instructions and a diagram of an activity that explains the fetch-execute cycle using volunteers from the class.
- Ideally you will require eight volunteers to perform this activity. If your class is large enough you may choose to split the learners into groups of eight.
- In this example we are adding the numbers 6 and 5 together, but feel free to add your own instructions and amend the activity in any way you wish.
ADDITIONAL RESOURCES
WJEC > A Level Computer Science > Specification from 2015
WJEC > A Level Computer Science > Specimen Assessment Materials
UNITS: 1 AND 4 EXAM LEVEL: AS/A
AREA OF STUDY
Sign and Magnitude and Two's Complement
Key Points:
- Learners should understand that there are two ways in which negative integers can be represented within computer systems.
- Questions on sign and magnitude and two's complement will relate to AO1 and AO2.
Provides an opportunity to develop the following skills: Speaking, Listening and understanding; Reading; Writing; Understanding numerical data; Carrying out calculations; Interpreting results; Presenting findings; Using ICT systems; Finding, selecting and exchanging information; Improving own learning and performance; Developing and presenting information using ICT; Working with others- plan do and review.
INSPIRATION FOR TEACHING
Example
Activity Name : Representing Negative Binary Numbers
- Ask for eight volunteers from the class and say that they are going to help demonstrate how negative integers can be represented using binary digits.
- Line up the volunteers at the front of the class and hand each of them a piece of card with a '1' on one side and a '0' on the other. Explain that each volunteer will represent a single bit.
- Ask the learners to represent the number 7 10 (00000111 2 ). Explain that when negative numbers are represented in 'sign and magnitude' form, the most significant bit is used to represent the sign of the number- '0' for positive and '1' for negative numbers. Ask the students to represent the number -7 10 (10000111 2 ).
- Explain to the learners that there is a second method used to represent negative integers, called 'Two's complement', a two-step process whereby all of the bits in the binary number are 'flipped' (0s to 1 and 1s to 0) and 1 is added, in this example -7 10 = 11111001 2.
- Ask the learners to represent other negative integers using both methods.
ADDITIONAL RESOURCES
WJEC > A Level Computer Science > Specification from 2015
WJEC > A Level Computer Science > Specimen Assessment Materials
UNIT: 3 EXAM LEVEL: A
AREA OF STUDY
Binary Trees
Key Points:
- Learners should understand that binary trees are useful data structures for rapidly storing and retrieving stored data.
- A binary tree has a root node, and every node has at most two children.
- Questions on binary trees will relate primarily to AO2.
Provides an opportunity to develop the following skills: Speaking, Listening and understanding; Reading; Writing; Understanding numerical data; Carrying out calculations; Interpreting results; Presenting findings; Using ICT systems; Finding, selecting and exchanging information; Improving own learning and performance; Developing and presenting information using ICT; Working with others- plan do and review.
INSPIRATION FOR TEACHING
Example
Activity Name : Sorting Numbers
- Split the class into pairs and give each pair squares of card/paper numbered 10, 6, 15, 8, 5, 11, 18, stacked in that order with 10 on top.
- Explain that you are going to show a method of sorting the cards in a way that will make it easier to find a specific number, but that you are NOT GOING TO PUT THEM INTO NUMERICAL ORDER.
- Arrange the 10, 6, 15 and 8 cards as in the picture on the left. Discuss the arrangement with the class.
- Ask learners to add the 5, 11 and 18 cards to the arrangement and to call out random numbers. Discuss with the class where these random numbers would be added to the tree.
- Ask learners to find card '18' by traversing the tree. Discuss how many comparisons this took and compare this with the number of cards that would have to be searched if the list were in ascending numerical order.
ADDITIONAL RESOURCES
WJEC > A Level Computer Science > Specification from 2015
WJEC > A Level Computer Science > Specimen Assessment Materials
UNIT: 3 EXAM LEVEL: A
AREA OF STUDY
Hash Tables
Key Points:
- Learners should understand that hash tables use a hash function to calculate an index value for an array, in which items can be stored or found.
- Questions on hash tables will relate primarily to AO2.
Provides an opportunity to develop the following skills: Speaking, Listening and understanding; Reading; Writing; Understanding numerical data; Carrying out calculations; Interpreting results; Presenting findings; Using ICT systems; Finding, selecting and exchanging information; Improving own learning and performance; Developing and presenting information using ICT; Working with others ‒ plan do and review.
INSPIRATION FOR TEACHING
Example
Activity Name : Arranging by First Names
- Tell the class that searching for their first name on an attendance register is not efficient, as their first names are not in any partiular order. So you want them to arrange their first name in order using the concept of a hash table.
- Split the learners into groups and give each group a piece of A4 paper with a hash function written on it, for example: Length of first name MOD (size of group –1)
- Tell the members of each group that they will form a line (hash table) by performing the hash function on their first name and standing in the calculated position.
- As the hash function given will result in two learners having the same hash number, there will be a clash and both will try to stand in the same place. Ask the class how this problem could be resolved?
- You may wish to suggest different methods of resolving the problem, such as the use of a larger hash table, allowing clashes and storing data in overflow areas or using an improved hashing algorithm.
ADDITIONAL RESOURCES
WJEC > A Level Computer Science > Specification from 2015
WJEC > A Level Computer Science > Specimen Assessment Materials
UNIT: 3 EXAM LEVEL: A
AREA OF STUDY
Big O Notation
Key Points:
- Learners should understand that Big O notation is used in computer science to describe the performance or complexity of an algorithm.
- Learners should know that Big O describes the worst-case scenario for the execution time required and the space used (e.g. in memory) by an algorithm.
- Questions on Big O notation may relate to AO1, AO2 or AO3.
Provides an opportunity to develop the following skills:
Speaking, Listening and understanding; Reading; Writing; Understanding numerical data; Carrying out calculations; Interpreting results; Presenting findings; Using ICT systems; Finding, selecting and exchanging information; Improving own learning and performance; Developing and presenting information using ICT; Working with others- plan do and review.
INSPIRATION FOR TEACHING
Example
Activity Name : Explaining Big O Notation in the Context of Different Algorithms
- Big O notation can be a difficult concept to grasp. However, learners who are confident in their understanding of algorithms may appreciate Big O notation being explained in the context of different algorithms.
- Explain to the class that an algorithm that will always execute in the same time, regardless of the size of the input data set, would be described as O(1).
- Select the image (left) for an example O(1) algorithm, examples of other algorithms and a table displaying the time and space complexity of common algorithms that you can use to discuss with the class.
- Ask the learners to carry out further research on other algorithms with different runtime performance characteristics.
ADDITIONAL RESOURCES
WJEC > A Level Computer Science > Specification from 2015
WJEC > A Level Computer Science > Specimen Assessment Materials
UNIT: 3 EXAM LEVEL: A
ALGORITHMS DESCRIBED IN THE CONTEXT OF BIG O NOTATION
O(N^2 ) represents an algorithm where the runtime performance is directly proportional to the number
of items in the data set squared.
Algorithms with a nested loop through the data set will always have a runtime performance of at least
O(N^2 ). Further nested loops will result in a runtime performance of O(N^3 ), O(N^4 ) etc.
In this algorithm, “duplicate found” will always be output when i=j, but to avoid confusion by using a
nested if, it has been omitted as it is the nested loop that increases the runtime to O(N^2 ).
1 declare myarray(1…n) is string
2 startmainprog
3 for i = 1 to n
4 for j = 1 to n
5 if myarray(i) = myarray(j) then
6 output “duplicate found”
7 endif
8 next j
9 next i
10 Endmainprog
The following table contains an overview of the time and space complexity of common algorithms:
Algorithm Time Complexity Space Complexity
Linear search 𝑂𝑂(𝑛𝑛) 𝑂𝑂( 1 )
Binary search 𝑂𝑂(log 2 𝑛𝑛) 𝑂𝑂(log 2 𝑛𝑛)
Bubble sort 𝑂𝑂(𝑛𝑛^2 ) 𝑂𝑂( 1 )
Insertion sort 𝑂𝑂(𝑛𝑛^2 ) 𝑂𝑂( 1 )
Quick sort 𝑂𝑂(𝑛𝑛 log 2 𝑛𝑛) 𝑂𝑂(log 2 𝑛𝑛)
Dijkstra graph search 𝑂𝑂(|𝑉𝑉|^2 + |𝐸𝐸|) 𝑂𝑂(|𝐸𝐸| log 2 |𝑉𝑉|).
UNIT: 3 EXAM LEVEL: A
AREA OF STUDY
Shortest-Path Algorithms
Key Points:
- Learners should understand that computer systems calculate the distance between two locations by determining all possible routes and finding the shortest path.
- Dijkstra's algorithm is an example that finds the shortest path between two vertices on a graph.
- Questions on Shortest-Path Algorithms will relate to AO1, AO2 and AO3.
Provides an opportunity to develop the following skills: Speaking, Listening and understanding; Reading; Writing; Understanding numerical data; Carrying out calculations; Interpreting results; Presenting findings; Using ICT systems; Finding, selecting and exchanging information; Improving own learning and performance; Developing and presenting information using ICT; Working with others- plan do and review.
INSPIRATION FOR TEACHING
Example
Activity Name : Wandering the School/College
Note: In this example, we will use the terms 'crossroad', 'corridor' and 'building'. However, in formal notation these terms are 'vertex', 'edge' and 'graph' respectively.
- Ask each learner to take three different routes from the classroom to the main reception or another location in the building.
- Learners should take a different corridor each time they reach a crossroad.
- Ask each learner to record carefully the number of steps taken for each route.
- When the learners have returned to the classroom ask them to each determine the shortest path of all three routes travelled.
ADDITIONAL RESOURCES
WJEC > A Level Computer Science > Specification from 2015
WJEC > A Level Computer Science > Specimen Assessment Materials