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Name: Class Teacher:
Date:
OCR H446 A-Level Computer Science
REVISION BOOKLET
1.3 EXCHANGING DATA
Content in H446 A-Level Computer Science: 1.1 The characteristics of contemporary processors, input, output and storage devices 1.2 Software and software development 1.3 Exchanging data 1.4 Data types, data structures and algorithms 1.5 Legal, moral, cultural and ethical issues 2.1 Elements of computational thinking 2.2 Problem solving and programming 2.3 Algorithms
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1.3.1 COMPRESSION, ENCRYPTION AND HASHING
TOPIC
Lossy vs Lossless Compression
Run length encoding and dictionary coding for lossless compression
Symmetric and asymmetric encryption
Different uses of hashing
1.3.1 COMPRESSION, ENCRYTPION AND HASHING
LOSSY COMPRESSION
LOSSLESS COMPRESSION RUN LENGTH ENCODING
DICTIONARY CODING
SYMMETRIC ENCRYPTION
ASYMMETRIC ENCRYPTION HASHING
1.3.2 DATABASES
TOPIC
Relational database
Flat file
Primary key
Foreign key
Secondary key
Entity relationship modelling
Normalisation
Indexing
Methods of capturing, selecting, managing and exchanging data
Normalisation to 3NF
SQL – Interpret and modify
Referential integrity
Transaction processing
ACID (Atomicity, Consistency, Isolation, Durability)
Record locking and redundancy
1.3.2 DATABASES
RELATIONAL DATABASE
FLAT FILE PRIMARY KEY FOREIGN KEY
SECONDARY KEY ENTITY RELATIONSHIP MODELLING
NORMALISATION INDEXING
METHODS OF CAPTURING, SELECTING, MANAGING AND EXCHANGING DATA
NORMALISATION TO 3NF SQL – INTERPRET AND MODIFY
REFERENTIAL INTEGRITY
TRANSACTION PROCESSING ACID (ATOMICITY, CONSISTENCY, ISOLATION, DURABILITY)
RECORD LOCKING AND REDUNDANCY
1.3.3 NETWORKS
TOPIC
Characteristics of networks and the importance of protocols and standards
The internet structure:
The TCP/IP stack
DNS
Protocol layering
LANs and WANs
Packet and circuit switching
Network security and threats:
Use of firewalls, proxies and encryption
Network hardware
Client-server and peer-to-peer
1.3.3 NETWORKS
CHARACTERISTICS OF NETWORKS
IMPORTANCE OF PROTOCOLS AND STANDARDS THE INTERNET STRUCTURE THE TCP/IP STACK
DNS
PROTOCOL LAYERING
LANs AND WANs
PACKET SWITCHING
CIRCUIT SWITCHING
NETWORK SECUITY AND THREATS FIREWALLS
PROXIES
ENCRYPTION
NETWORK HARDWARE
CLIENT-SERVER PEER-TO-PEER
1.3.4 WEB TECHNOLOGIES
TOPIC
HTML, CSS and JavaScript
Search engine indexing
PageRank algorithm
Server and client-side processing
1.3.4 WEB TECHNOLOGIES
HTML CSS
JAVASCRIPT
SEARCH ENGINE INDEXING PAGERANK ALGORITHM
SERVER AND CLIENT-SIDE PROCESSING
EXAM QUESTIONS
QUESTION 1 a. The office workers of a large company each use a stand-alone computer. The
company is considering networking the machines. Describe what is meant by a LAN.
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State two advantages of having a LAN instead of a set of stand-alone machines. ……………………………………………………………………………………………………………………………………………
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[2] b. Describe the following types of data transmission:
Serial data transmission ……………………………………………………………………………………………………………………………………………
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[2] Full duplex …………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………
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QUESTION 2 Laser Tag is a game where teams of players move round an arena shooting each other with
infrared guns. Players wear sensors that keep track of how many times they have been hit by the laser. This is known as being ‘tagged’. Below is an extract from a Laser Tag company’s website:
a. The web page is written in HTML.
Write some HTML code which could have been used to produce this extract. You can assume it is already inside <body> tags.
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b. The website also includes JavaScript. Describe what is meant by the term JavaScript.
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Explain why it is usually the case that JavaScript is interpreted rather than compiled.
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QUESTION 3 A software company decides to release a duplicate file finder which it has names “De-
Duplicator”. Duplicate files are files that are exactly the same (bit for bit identical). Space is often wasted on computers by having multiple versions of the same file. Duplicate file finders are programs that find and identify duplicate files on a hard drive so that they can be removed. Every time the program encounters a file it takes a hash of the file and checks it against a list. If the hash exists in the list, the file is marked to be deleted. If the hash does not exist, it is added to the list.
a. Explain two characteristics you would look for in a hashing algorithm for this
purpose. …………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………
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b. After running the program, a user finds that they still have apparent duplicates of some of their images. Explain why these apparent duplicates might still be present.
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QUESTION 4 The Big Brains exam board has produced a website that allows students to access revision
videos. All pages in the site contain the following tag in the head section. <link href=”themes/standard.css” rel=”stylesheet” type=”text/css” />
Describe one advantage of storing the CSS in an external file rather than it being embedded within HTML files. …………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………
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[3] The exam board wants to limit access to those students with a school email account (i.e. one ending sch.uk). When students sign up, JavaScript is used to check that the email address they have entered is from a school account. The address is checked again when it reaches the server before login details are sent to the address. Explain why it is important to check the email address with JavaScript and again when it
reaches the server. ……………………………………………………………………………………………………………………………………………
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[3]
The video table consists of the following fields: VideoID, VideoName, Presenter, Topic. Describe what is meant by the term primary key.
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[2]
Write an SQL query that finds the name and presenter of all videos on the topic of “The
CPU”. …………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………
[4]
The exam board wants to use a database to keep track of which videos each student has
viewed. The structure it plans to use is shown below:
Identify one reason why this structure would not be suitable.
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[1]
Draw a new version of the structure to solve this problem.
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QUESTION 5 A school has three independent computer networks.
One for student use. One for teacher use. One for use in the administration offices. The three networks are going to be combined to allow data to be stored in one location. The data will be accessible at any computer if the correct access codes are used. Explain how the following devices may be used in the above situation. A bridge
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[2] A gateway
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QUESTION 6 A company sells garden furniture. It has decided to create a relational database. A first,
incomplete database design includes two tables PRODUCT and ORDER. PRODUCT (ProductID, ProductType, Size, Price, …) ORDER (OrderID, OrderDate, ProductID, …) For example, the product which has ProductID 12345 is a large bench which has a price of £150. State one additional piece of data which should be included in PRODUCT and give one reason why it is needed. ……………………………………………………………………………………………………………………………………………
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[2] You should use only the data given above. Explain the use of a primary key in this database.
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[2] Explain the use of a foreign key in this database.
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A CUSTOMER table is added. An entity-relationship (ER) diagram is shown.
Explain why this design would be inefficient for customers. …………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………
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Some of the Structured Query Language (SQL) for this database is SELECT Surname, Title, PhoneNo
FROM CUSTOMER
WHERE Town = “Coventry”
ORDER BY Surname
Describe the purpose of this code and give one situation in which it may be used. …………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………
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QUESTION 7 A programmer spends her spare time contributing to an open source application that
converts video files from a range of formats to one which uses lossy compression. Describe what is meant by the term ‘lossy compression’. …………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………
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QUESTION 8 Every bank account has an account number and sort code. The sort code identifies the bank
branch (location of the bank) with which the account is held and the account number uniquely identifies the bank account. An extract from a bank’s database table is shown in Fig 5.1.
State why the table in Fig 5.1 is not in Third Normal Form. ……………………………………………………………………………………………………………………………………………
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Explain how the database could be put into Third Normal Form. …………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………
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A bank needs to ensure the data stored in its database is accurate at all times including when customers deposit or withdraw funds.
Discuss how the bank can ensure the accuracy of its data and the importance of doing so. …………………………………………………………………………………………………………………………………………… …………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………
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