AS CS Long Answer Questions (Revision) #1 Flashcards

Question

Describe how a single page is printed on a laser printer (7 steps).

Answer 1

1. A laser beam and a rotating mirror are used to draw an image of the page on the photosensitive drum. 2. The image is converted on the drum into an electrostatic charge. 3. Electrostatic charge attracts toner. 4. The charged paper is rolled against the drum. 5. The oppositely charged paper picks up the toner particles from the drum. After picking up the toner, the paper is discharged to stop it clinging to the drum. 6. The paper passes through a fuser, which heats up the paper. The toner melts and forms a permanent image on the paper. 7. The electrical charge is removed from the drum, and the excess toner is collected.

Answer 2

1. DRAM is constructed from transistors and capacitors that require a constant power to retain data, whereas SRAM uses flip-flops to hold each bit of memory. 2. SRAM is significantly faster than DRAM, making SRAM ideal for the memory cache while DRAM is used for main RAM modules. 3. DRAM is volatile, while SRAM is non-volatile 4. DRAM is less expensive to manufacture per unit storage, consumes less power, and has a higher memory capacity, storing more bits per chip than SRAM (higher memory density).

Answer 3

1. An electric current is sent to the speaker. 2. The electric current passes through the coil. 3. The current in the coil creates an electromagnetic field. 4. Changes in the audio signal cause the direction of the electrical current to change. This determines the polarity of the electromagnet. 5. The electromagnet is repelled by or attracted to the permanent magnet. 6. The movement of the coil causes the diaphragm to vibrate. 7. The vibration creates sound waves.

Answer 4

1. The object is designed in Computer Aided Design (CAD) software. 2. The software splits the object into slices. 3. The data about the slices is sent to the printer. 4. The solid plastic is melted and transferred to the nozzle. 5. A stepper motor moves the nozzle into position. 6. The nozzle extrudes the molten plastic. 7. The steps 5 to 6 repeat until the layer is complete. 8. A fan cools the layer. 9. The steps 4 to 8 are repeated for each subsequent layer.

Answer 5

1. Resistive screens use two layers, seperated by a thin space, that close a circuit when a user presses the top layer and causes the layers to touch. The horizontal and vertical position is transmted to the processor. 2. Capacitive screens use a glass layer that stores charge. A change (decrease) in the electric field is detected when a conductive finger touches the surface. The coordinates where the decrease in charge occurs is calculated and sent to the processor.

Answer 6

Hard disk drive (HDD): 1. less expensive per unit storage.. 2. Larger storage capacity than the flash drive. 3. Has more longevity. Solid state drive (SSD): 1. No moving parts, more reliable. 2. Lower power consumption than HDDs, runs cooler. 3. Robust. 4. Low latency.

Answer 7

Solid state memory has no moving parts and is non-volatile. It makes use of arrays of NAND and NOR gates to store data. SSD controller manages these components. Solid state memory uses a grid of columns and rows that has two transistors at each intersection. One transistor is called the floating gate (stores the charge) and the other is called the control gate (controls the flow of charge). Memory cells store voltages which can represent either a 0 or a 1.

Answer 8

RAM (Random Access Memory) is volatile memory, stores data that is currently being used in applications or services; its contents are lost when power is cut. ROM (Read-Only Memory) is non-volatile and stores permanent startup instructions, such as the start up instructions, OS kernel, or BIOS.

Answer 9

1. Light is emitted and bounces back off the document. 2. Reflected light falls on to mirrors. 3. Mirrors reflect refflected light back to CCD sensors. 4. Light is turnned into voltage based on light intensity. 5. The brighter the reflected light the higher voltage detected for the image document.

Answer 10

Register roles: • PC (Program Counter): Holds the address of the next instruction to be fetched; incremented after each fetch. • MAR (Memory Address Register): Holds the address to fetch data from (copied from PC). • MDR (Memory Data Register): Holds the data at the address in MAR. • CIR (Current Instruction Register): Stores the instruction currently being decoded/executed. Register Transfer Notation (RTN) — Fetch Stage: 1. MAR ← [PC] (contents of PC copied into MAR) 2. PC ← [PC] + 1 (PC incremented to point to next instruction) 3. MDR ← [[MAR]] (data at the address in MAR copied into MDR) 4. CIR ← [MDR] (contents of MDR copied into CIR for decode & execute) Full cycle stages: 1. Address in PC is the address of the next instruction to be fetched. 2. Address copied into MAR via the address bus. 3. Instruction copied from main memory to MDR via the data bus. 4. Instruction transferred from MDR to CIR. 5. Instruction decoded in CIR into opcode and operand. 6. Processor executes the instruction. 7. PC incremented ready for the next loop.

Answer 11

Detected: At the start/end of each F-E cycle (the processor checks the interrupt register). Handled: 1. The interrupt is given a priority and placed in the interrupt queue. 2. Processor finishes the current Fetch-Decode-Execute cycle and checks the interrupt register. 3. If lower priority than current process: continue with F-E cycle. 4. If higher priority than current process: — Current process state and registers are saved on the stack in memory. — Location/type of interrupt identified. — Appropriate Interrupt Service Routine (ISR) is called. 5. ISR handles the interrupt. 6. When ISR is finished: check for further high-priority interrupts / return to step 1. 7. Otherwise: load data from stack and continue with the original process.

Answer 12

• Clock speed — higher clock speed means more F-E cycles per second, so more instructions are executed per second. • Number of cores — more cores mean more instructions can be carried out simultaneously, reducing time to complete tasks. • Bus width — a wider bus allows the transfer of more data each clock cycle // allows more memory locations to be directly addressed. • Cache size — higher capacity cache means more frequently used instructions can be stored for fast access, reducing the need to fetch from slower RAM. Note: Cache is faster than RAM; RAM is faster than secondary storage.

Answer 13

1. Special purpose registers hold the status of the program whereas general purpose registers hold the temporary data used while preforming operations. 2. Special purpose registers are specialised for a specific use, whereas general purpose registers are used for any purpose. 3. General purpose registers can be used by most instrcutions, whereas special purpose registers can only be used by certain instructions.

Answer 14

1. The computer reads the assembly language program one line at a time. 2. Generate the object code, including the opcode and operand, from the symbol table generated in Pass 1. 3. Forward references are resolved. This is required as some labels may be refered to before their address is known. 4. Symbolic adresses are replaced by absolute references. 5. Save or execute the program.

Answer 15

1. Immediate Addressing: The value of the operand IS the data; used directly. e.g. LDM #200 loads the number 200 into ACC. 2. Direct / Absolute Addressing: The operand is the address of the data. e.g. LDD 200 loads the value stored at memory address 200. 3. Indirect Addressing: The operand gives the address of a memory location that contains the actual address of the data. e.g. LDI 200 — if address 200 contains 50, and address 50 contains 10, loads 10 into ACC. 4. Indexed Addressing: Effective Address = Operand + Index Register (IX). e.g. LDX 200 with IX=4 → accesses address 204. 5. Relative Addressing: Effective Address = Current address + Operand (used with JMR). e.g. JMR #5 transfers control to the instruction 5 locations ahead. 6. Symbolic Addressing: Only used in assembly; a label is used instead of a memory address. e.g. LDD MyStore — if MyStore is at address 300, loads value at 300. Labels make programs easier to modify (no need to manually update absolute addresses).

Answer 16

Pass 1: 1. Checks syntax of each line and removes all comments. 2. Builds a Symbol Table: when a symbolic address is first encountered, it is added with its current address, or marked 'unknown' if not yet defined (a forward reference). 3. Creates a Literal Table if the programmer has used constants in the program. 4. Performs Macro Expansion: replaces each macro call with its defined group of instructions. 5. Acts upon Directives (e.g. reserving memory, setting origin points); directives do NOT generate machine code. Pass 2: 1. Reads the assembly program one line at a time. 2. Generates the object code (opcode + operand) using the symbol table from Pass 1. 3. Resolves all forward references — replaces 'unknown' symbolic addresses with now-known absolute addresses. 4. Saves or executes the completed object program. After Pass 2: A Loader is required to load the object code into memory before it can be executed.

Answer 17

Data Movement: • LDM #n — Load immediate value n into ACC • LDD — Load contents of address a into ACC (direct) • LDI — Load using indirect addressing • LDX — Load using indexed addressing (EA = a + IX) • STO — Store ACC at address a • LDR — Load Index Register from ACC Arithmetic & Logic: • ADD / SUB — Add to or subtract from ACC (immediate #n or address) • INC / DEC — Increment or decrement ACC or IX • AND / OR / XOR — Bit manipulation using mask operand • LSL n / LSR n — Logical shift left/right n places (zeros fill vacated bits) Comparison & Control Flow: • CMP #n / CMP — Compare ACC with value (must precede JPE/JPN) • JPE — Jump if equal (previous CMP was True) • JPN — Jump if not equal (previous CMP was False) • JMP — Unconditional jump (changes PC to address a) • END — Return control to the OS I/O: • IN — Read one character from keyboard; stores ASCII value in ACC • OUT — Output character in ACC to screen Prefixes: # = immediate value; & = hexadecimal; B = binary

Answer 18

Cyclic Shift (Circular Shift / Rotation): • No bits are lost — bits shifted out of one end are re-introduced at the opposite end of the register. • Cyclic Left Shift: The leftmost (MSB) bit is removed and placed at the rightmost (LSB) position; all other bits shift left by one. • Cyclic Right Shift: The rightmost (LSB) bit is removed and placed at the leftmost (MSB) position; all other bits shift right by one. • Does NOT have the ×2 / ÷2 mathematical effect of logical/arithmetic shifts (because bits are rotated, not lost). Comparison of all three shift types: ┌─────────────┬─────────────────────────────────────────┬────────────┐ │ Shift Type │ What happens to shifted-out bit? │ Sign kept? │ ├─────────────┼─────────────────────────────────────────┼────────────┤ │ Logical │ Lost; vacated end filled with 0 │ No │ │ Arithmetic │ Lost; MSB preserved on right shift │ Yes │ │ Cyclic │ Re-introduced at the opposite end │ N/A │ └─────────────┴─────────────────────────────────────────┴────────────┘ Use cases: Pattern detection, bit-level encryption, rotating bit flags in monitoring/control applications.

Answer 19

• Disk formatter: Sets up a disk so it is ready to store files. • Defragmentation: Moves parts of files so that each file is contiguous in memory. • Back-up: Creates a copy of data in case the original is lost. • Disk repair: Scans for errors in a disk and corrects them.

Answer 20

• Storage space is divided into file allocation units. • Space is allocated to particular files. • Maintains/creates directory structures. • Specifies the logical method of file storage (e.g. FAT or NTFS). • Provides file naming conventions. • Controls access // implements access rights // implements password protection // makes file sharing possible. • Specifies tasks that can be performed on a file (e.g. open, close, delete, copy, create, move).

Answer 21

• Defragmentation — less time taken to access files because each file is stored contiguously on disk, so there is less read/write head movement. • Virus checker — makes more RAM available for programs to run, because it removes malicious software that might be taking up memory / replicating. • Disk repair / Disk contents analysis — prevents bad sectors from being used (identifies and marks them); reduces access times by optimising storage. • Disk/system clean up — releases storage by removing unwanted/temporary files. Note: Defragmentation improves HDD performance but is NOT needed for SSDs (no moving parts; file location doesn't affect speed).

Answer 22

• Saves (programming/testing) time — code does not have to be written/re-written from scratch // code does not have to be tested. • Code is already tested so it is more robust/likely to work. • If there is an improvement in the library routine the program updates automatically. • Can perform complex calculations that the programmer may be unable to do themselves.

Answer 23

1. Operating system updates: Keeps the system secure by implementing updates as they become available. 2. Antivirus and security software updates: Ensures that antivirus and other security software is up to date. 3. Firewall communication: Monitors all incoming and outgoing traffic, and checks for suspecious files. 4. User privalges: Restricts access to private areas on multi-user systems, by using user accounts, passwords and UserIDs to protect data 5. Access rights: Manages access permissions for all users. 6. Data recovery and system restore: Allows data and system recovery in case of corruption or loss. 7. Prevention of illegal intrusion: Prevents unauthorised access to ensure privacy and data integrity.

Answer 24

1. Single (contiguous) allocation: Allocates all memory to a single application. 2. Partitioned allocation: Divides memory into contiguous blocks assigned to applications with variable partition size. 3. Paged memory: Similar to partitioned allocation, but each partition is a fixed size. 4. Segmented memory: Memory blocks are not contiguous, each segment is a logical grouping of data, such as an array.

Answer 25

The part of the operating system that controls and manages the main memory. It preforms the following subtasks: 1. Memory protection. 2. Use of virtual memory. 3. Allocates and deallocates memory to processes. 4. Manages location of processes within the memory.

Answer 26

The part of the OS that controls all input/output devices connected to the computer through sub-management systems. Some of which are: 1. Installation of appropriate driver software. 2. Controls access to data being sent to/from hardware and peripheral devices. 2. Manages communication between devices.

Answer 27

1. Creates a copy of the contents of a disk /partition. 2. Can be set up to automatically backup. 3. Allows the user to decide what is backed up, e.g. all data /all files that have changed since the last backup. 4. Allows the user to set up an off-site backup. 5. Restores the data if necessary.

Answer 28

It is software that protects systems by running in the background, detecting and removing viruses. It works by: 1. Scans files before they are opened. 2. Checks against a virus database. 3. Conducts heuristic checks on files. 4. Quarantines files.

Answer 29

Virtual Memory: A technique used by the OS to simulate more RAM than is physically available, by using part of secondary storage (HDD/SSD) as an extension of RAM. How it works: 1. The OS divides programs and data into fixed-size pages. 2. Only the pages currently needed are loaded into RAM (physical memory). 3. Pages not currently needed are stored in a page file (swap space) on secondary storage. 4. When a required page is NOT in RAM, a page fault occurs: — The OS identifies a page in RAM that is not currently needed. — That page is written to secondary storage. — The required page is loaded into the freed RAM space. Benefits: Allows programs larger than available RAM to run; enables multitasking. Drawbacks: Accessing secondary storage is much slower than RAM — if used excessively, performance degrades severely (known as "thrashing"). Memory Management subtasks: memory protection, use of virtual memory, allocating/deallocating memory to processes, managing process locations within memory.

Answer 30

Interpreter: • Use an interpreter while writing/developing the program. • To test/debug the partially completed program. • Because errors can be corrected and processing continues from where the execution stopped // errors can be corrected in real time // errors are identified one at a time. Compiler: • Use the compiler after the program is complete. • To create an executable file. • Use the compiler to repeatedly test the same (completed) section without having to re-interpret every time // compiler not needed at runtime.

Answer 31

Debugging tools: • Breakpoints — stops the code executing at a set line. • Single stepping — executes one line of the program and then stops. • Report windows — outputs the contents of variables and data structures. Writing/support tools: • Colour coding // pretty printing. • Auto-complete. • Auto-correct. • Context-sensitive prompts — displays predictions of the code being entered. • Dynamic syntax check — underlines or highlights statements that do not meet the rules of the language. • Expand and collapse code blocks.

Answer 32

1. The code is already written so the programmer is not starting over again which saves time. 2. The code will have been used by many people so it should be already thoroughly tested and relatively error-free / won’t need re-testing. 3. The programmer can use e.g. mathematical / graphics functions that he may not know how to code. 3. Use of named library functions can simplify the program and make it easier to read. 4. The library routine code should conform to industry standards and therefore contribute towards a more robust program.

Answer 33

1. Compiler creates an executable//an interpreter does not create an executable. 2. The compiled program can be independently distributed. 3. Compiler reports all errors at the end of compilation//an interpreter stops when it reaches an error. 4. Interpreter executes each statement immediately after decoding/checking it. 5. The compiled program does not require compiler/source code to be present.

Answer 34

1. Easier de-bugging. 2. The interpreter stops when error encountered, so errors can be corrected in real time. 3. The interpreter translates a statement then executes it immediately. 4. Parts of the program can be tested, without all the program code being available.

Answer 35

Similarities: 1. Both are pieces of malicious software. 2. Both are downloaded/installed/run without the user's knowledge. 3. Both can pretend to be / are embedded in other legitimate software when downloaded // both try to avoid the firewall. 4. Both run in the background. Differences: 1. A virus can damage/delete computer data; spyware only records/accesses data. 2. A virus does NOT send data out of the computer; spyware sends recorded data to a third party (often via keylogging). 3. A virus replicates itself; spyware does NOT replicate itself.

Answer 36

• Access rights assign different levels of permission to different user accounts/logins (e.g. read-only // no access // read/write). • Specific views can be assigned to different users so they can only see the data relevant to them (e.g. managers can only see data for their own shop(s)). • Prevents unauthorised users from accessing sensitive data (e.g. a hospital cleaner cannot access patient records, but a consultant can). • User accounts with unique UserIDs and passwords are used to authenticate users before applying access rights.

Answer 37

1. A timer is started when sending decice transmists a data packet to receiver. 2. Receiving device checks the data packet for errors (using any error checking method). 3. Once the receving device knows that the packet is error free it sends an acknowledgement back to sending device. 4. The next packet is sent. 5. If the sending device does not receive an acknowledgement before the timer ends. 6. A time out occurs. 7. The data packet is resent. 8. Until acknowledgment is recieved or maximum number of attempts reached.

Answer 38

1. The sender hashes the document. 2. To produce a digest. 3. The sender encrypts the digest with a private key to create the digital signature. 4. The document and the signature are sent to the user. 5. The user uses the public key to decrypt the digital signature to reproduce the digest. 6. The digital signature can only be decrypted with matching sender's public key. 7. The receiver uses the same hashing algorithm on the document received to produce a second digest. 8. If both of the receiver's digests are the same, the document has not been changed.

Answer 39

1. Total of several fields of data is calculated using a hashing algorithm. 2. Including fields not usually used in calculations. 3. The result is transmitted with the data. 4. Calculation repeated at receiving end using the same algorithm. 5. Results are compared. 6. If the values are different an error has occurred.

Answer 40

If an incoming transmission is an email, there can be a concern about the authenticity of the email's sender. The solution is to insist on the sender attaching a digital ciertificate to the email. The digital cirtificate can also be an electronic document confirming the identity and security-ability of a web page on the internet. It is defined as an electronic document used to prove the ownership of a public key (used for encryption).

Answer 41

1. Examining incoming and outgoing traffic between the user's computer and the internet. 2. Checking if incoming or outgoing data meets a given set of criteria. 3. If the data fails the criteria, the firewall will block the traffic and gives the user a warning that there may be a security issue. 3. Logging all incoming and outgoing traffic for later interrogation by the user.

Answer 42

1. The browser sends a request. 2. The web server responds with an SSL/TLS certificate 3. If the browser authenticates the certificate, it sends a message to the web server. 4. Once this message is received by the web server, the server acknowledges the web browser and a SSL-encrypted two-way data transfer begins.

Answer 43

1. A calculation is done, using an algorithm, on a block of data to produce a value. 2. The result is transmitted with the data. 3. Calculation repeated at receiving end using the same algorithm. 4. Results are compared. 5. If the values are different an error has occurred.

Answer 44

1. The number of 1 bits are counted. 2. A parity bit is added to each byte (7 bits BEFORE transmission). 3. The bit is added to make the sum of the 1 bits in each byte odd. 4. After transmission, if the number of 1 bits is odd, no error is detected. 5. After transmission, if the number of 1 bits is even, an error is detected.

Answer 45

1. Range Check: Ensures data falls within a specified minimum and maximum range. e.g. age between 0 and 120. 2. Type Check: Ensures data is of the correct data type. e.g. numbers only, or text only. 3. Length Check: Ensures data is a specific number of characters. e.g. a 10-digit phone number. 4. Presence Check: Ensures mandatory fields are not left blank. 5. Format Check: Ensures data matches a specific pattern. e.g. date in DD/MM/YYYY format. 6. Lookup Check: Ensures data matches a value from a pre-defined set/list. e.g. country codes. 7. Check Digit: An extra digit appended to a code; computed from the other digits. Used to detect: incorrect digit entry, transposition errors (swapped digits), and phonetic errors. KEY LIMITATION: Validation checks that data is REASONABLE / SENSIBLE, but CANNOT check whether the data is actually correct or accurate. (e.g. a valid age of 25 might still be the wrong person's age.)

Answer 46

These questions need five types of answer: 1. A form of being fair. 2. A form of building trust within a team. 3. A form of working as a team. 4. A form of feeling valued, getting help, giving help. 5. A form of producing the best product for the client and employer.

Answer 47

• Has clear, laid-out ethical guidelines to follow — so clients/other staff know the standards being applied and he does not have to decide what is ethical; it is written down. • Clients/staff know he is reputable — recognition of skills/knowledge; there may be a test/requirements for entry. • Access to legal advice if action is taken against them. • They provide help and support (e.g. if legal advice is needed). • Networking opportunities — no missing out on contacts/jobs. • They run training courses to keep skills up-to-date; access to professional development.

Answer 48

• Tell the manager they have not used it and explain how they will get up-to-date. • Perform their own research on how to use it. • Explain to the manager that additional training is needed. • Ask the manager to book a training course. • Ask for a mentor / to shadow someone more experienced. • Practise at home before starting.

Answer 49

1. Product Key — unique reference number entered during installation 2. Licence Agreement — user must agree to terms before installation 3. Genuine Packaging — hologram sticker/label warning copying is illegal 4. Hardware Restrictions — software only works when original media (CD/DVD/USB) is present 5. Dongle — hardware device plugged into USB port required for software to function

Answer 50

1. The rules/past moves/decision-making algorithms are stored 2. The AI program is trained by repeating the process many times 3. The AI looks ahead at possible scenarios and/or analyses patterns of past choices 4. The AI chooses the move most likely to be successful 5. The computer learns to improve by storing positive/negative results of choices and changing future choices accordingly

Answer 51

1. Making and distributing copies for sale or to give away 2. Using software on a network/multiple computers without a multi-use licence 3. Using code from copyrighted software to create and distribute new software without the copyright holder's permission 4. Renting out a software package without the copyright holder's permission 5. Using the name of copyrighted software on other software without permission

Answer 52

Original purpose: DRM was initially developed to control what devices a CD could play on, reducing illegal copying (e.g. preventing CDs from being copied onto computers). Expansion: DRM now applies to music tracks, video files, ebooks, and more. Example of DRM Licensing: Apple Music uses DRM to prevent downloading all music during the trial month and then cancelling the subscription.

Answer 53

Software available free initially (as a trial). The full version becomes accessible only after paying the full fee. Key points: • Trial version may be feature-limited • Users cannot access/modify source code • After payment, users receive updates and support • Users must not repurpose the source code without permission

Answer 54

1st Law: A robot may not harm a human being or, through inaction, allow a human being to come to harm. 2nd Law: A robot must obey orders given by humans, except where this would conflict with the First Law. 3rd Law: A robot must protect its own existence, as long as this does not conflict with the First or Second Law.

Answer 55

• Paid software; protected by copyright law. • Users CANNOT modify the source code. • Users CANNOT redistribute copies of the software. • Available as a single-use or multi-use (network/site) licence. • Protected by anti-piracy measures: product keys, licence agreements, DRM, hardware restrictions, dongles. • Users typically receive updates and support while their licence is valid. • Illegal actions: making/distributing copies, using on multiple machines without a multi-user licence, renting out software without permission.

Answer 56

Definition: Software that is free to use, study, modify, and redistribute. Source code must be provided/accessible. The Four Freedoms (FSF): • Freedom 0: Run the software for any legal purpose. • Freedom 1: Study and modify the source code. • Freedom 2: Redistribute copies of the software. • Freedom 3: Share modified code with others. (Access to source code is a prerequisite for Freedoms 1 and 3.) Restrictions on users: • Cannot integrate code from copyrighted (proprietary) software. • Cannot create software that mimics copyrighted software. • Cannot adapt source code in ways that infringe on other copyrighted software. Key distinction: • FSF (Free Software Foundation): Focuses on user RIGHTS and moral/ethical stance. • OSI (Open Source Initiative): Emphasises PRACTICAL BENEFITS — collaborative development and business value.

Answer 57

Freeware: • Software available for free download at no cost. • Still covered by copyright laws (the developer retains full copyright). • Users CANNOT modify the source code. • Users CANNOT repurpose the code in other software. • Users CANNOT resell the software. • Source code is NOT provided. Key difference from Free/Open Source: • Freeware = free to use, but no access to or rights over the source code. • Free/Open Source = free to use AND free to modify/redistribute with source code access. Examples: Free antivirus tools (basic tier), PDF readers.

Answer 58

COMMERCIAL (Proprietary): • Cost: Paid. Copyright-protected. Cannot modify or redistribute. • Single/multi-use licence. Anti-piracy measures enforced. FREE/OPEN SOURCE (FSF/OSI): • Cost: Free. Can run, modify, redistribute, and share modified code. • Source code must be included. Cannot integrate proprietary code. FREEWARE: • Cost: Free. Cannot modify, repurpose, or access source code. • Still copyright-protected. No redistribution rights. SHAREWARE: • Cost: Free trial initially (may be feature-limited). Must pay after trial. • No source code access. Paying users receive full version, updates, and support. • Users must not repurpose source code without permission.

Answer 59

Problems with file-based / flat-file systems: 1. Data redundancy — same data is stored many times across multiple files. 2. Program-data dependence — any changes to the data structure means all programs that access that data have to be re-written. 3. Data inconsistency / poor data integrity — duplicated data might be stored differently; updating data in one file does not update it everywhere. 4. Not easy to perform complex searches/queries — a new program has to be written each time. 5. Lack of privacy — user views cannot easily be implemented. Advantages of relational database: 1. Reduced data redundancy — each data item stored only once. 2. Data consistency / improved integrity — changes in one table automatically reflected in linked tables. 3. Program-data independence — structural changes do not require programs to be re-written. 4. Complex queries are easier to run (using SQL). 5. Can provide different views — users only see the specific data they are authorised to see.

Answer 60

Purpose: Stores metadata — data about the data within the database. Contents: • Field / attribute names • Table name(s) • Data types for each field • Primary keys // foreign keys • Validation rules • Relationships between tables • Indexing details How it enhances integrity: By defining validation rules, data types, and key constraints within the dictionary, the DBMS ensures accuracy, completeness, and consistency of all data. Key distinction from Logical Schema: • Data Dictionary = metadata about attributes and validation rules (tabular). • Logical Schema = conceptual model of entity relationships (often an E-R diagram).

Answer 61

• Candidate Key: The smallest set of attributes that can uniquely identify a record without duplication. A table may have multiple candidate keys. • Primary Key: The specific candidate key chosen by the designer as the unique identifier for the table. Must be unique and NOT NULL. • Composite Key: A primary key made up of two or more attributes that together uniquely identify a record (used when no single attribute is sufficient alone). • Secondary Key: An alternative identifier used to provide additional search/access paths without replacing the primary key. • Foreign Key: An attribute (or set) in one table that references the primary key of another table. Creates a link between tables and enforces referential integrity. Referential Integrity: Every foreign key value must match an existing primary key value in the referenced table. A primary key cannot be deleted while dependent foreign key records exist (unless cascading is used).

Answer 62

Purpose of an E-R Diagram: Visual representation of database entities and the relationships between them. Design steps: 1. Identify entities — typically the "nouns" in the requirements (objects, people, events about which data is stored). 2. Identify relationships between entities. 3. Define cardinality for each relationship. Relationship types: • One-to-One (1:1): Each record in Table A corresponds to exactly one record in Table B. • One-to-Many (1:M): One record in Table A links to multiple records in Table B. • Many-to-Many (M:M): Multiple records in A relate to multiple records in B. → Resolved by creating a link/junction table, converting the M:M into two 1:M relationships. Cardinality: Defines the nature and numerical obligation of a relationship: • Mandatory: Each entity instance MUST relate to at least one instance of the other entity. • Optional: An entity instance does NOT need a corresponding instance in the related entity. Reading relationships (bidirectional): e.g. "One Band is booked for many Bookings" (forward) / "One Booking is for one Band" (backward).

Answer 63

Definition: A table is in 1NF when: 1. It contains NO repeating groups of attributes. 2. Every attribute value is ATOMIC — each cell contains only a single, indivisible value. Repeating group: When a single attribute contains multiple data values for one entity instance (e.g. a "Subjects" column containing "Maths, Physics, English"). How to convert to 1NF: • Identify and remove all repeating groups. • Ensure each cell holds only one value (make atomic). • Each row must be uniquely identifiable — a primary key must exist (may need to be composite). • Duplicate rows may need to be broken into separate rows. Output: A flat table with a primary key and no repeating attributes.

Answer 64

Definition: A table is in 2NF when: 1. It is already in 1NF. 2. There are NO partial dependencies — every non-key attribute depends on the WHOLE primary key, not just part of it. Note: Partial dependencies only occur when the primary key is COMPOSITE (two or more attributes). If the primary key is a single attribute, 1NF ⟹ 2NF automatically. Partial dependency: A non-key attribute that is determined by only one part of a composite primary key. e.g. In (StudentID, CourseID) → CourseName: CourseName only depends on CourseID, not StudentID. How to convert to 2NF: 1. Identify all partial dependencies. 2. Move partially dependent attributes into a new table, with the relevant part of the key as the new primary key. 3. Leave a foreign key in the original table to link to the new table. Output: All non-key attributes depend on the full composite key.

Answer 65

Definition: A table is in 3NF when: 1. It is already in 2NF. 2. There are NO transitive (non-key) dependencies — every non-key attribute depends ONLY on the primary key. The Normalization Litany: Every non-key attribute must depend on "the key, the whole key, and nothing but the key." Transitive dependency: A non-key attribute depends on another non-key attribute (rather than directly on the primary key). e.g. StudentID → PostCode → Town: Town depends on PostCode (non-key), not directly on StudentID. How to convert to 3NF: 1. Identify all transitive dependencies (non-key → non-key). 2. Move the transitively dependent attribute(s) into a new table, with the determining non-key attribute as the new primary key. 3. Leave a foreign key in the original table to link back. Output: All non-key attributes depend directly and only on the primary key. Summary of three stages: • 1NF: No repeating groups; all values atomic. • 2NF: 1NF + no partial dependencies (full dependency on whole key). • 3NF: 2NF + no transitive dependencies (depends on nothing but the key).

Answer 66

Key DBMS components: • Data Dictionary: Stores metadata (field names, data types, validation rules, keys, relationships, indexing). • Logical Schema: Conceptual model of data structure; independent of the DBMS software. • Query Processor: Processes and executes SQL queries. • DDL Interpreter: Interprets Data Definition Language statements; records them in the data dictionary. • DML Compiler: Compiles Data Manipulation Language statements; optimises them for efficient execution. • Developer Interface: Allows developers to write complex SQL, create/modify objects, design reports and data-entry forms. DBMS Security Measures: 1. Usernames and passwords — authenticate users. 2. Access rights — control what each user can read/write/delete. 3. Automated back-ups — scheduled copies to prevent data loss. 4. Data encryption — protects data in storage and in transit. 5. Audit trails — logs all user actions for monitoring access and detecting unauthorised activity. How DBMS addresses file-based problems: • Redundancy: Most data stored once; foreign keys are the exception. • Inconsistency: Single-store updates are universally visible. • Data dependency: Structural changes minimally impact unrelated applications.

Answer 67

DDL — Data Definition Language (creates/modifies structure): • CREATE DATABASE db_name • CREATE TABLE table_name (col datatype PRIMARY KEY, ...) • ALTER TABLE — modify existing table (add/drop columns) • PRIMARY KEY — sets column(s) as unique identifier • FOREIGN KEY col REFERENCES other_table(col) — enforces referential integrity SQL Data Types: CHARACTER (fixed), VARCHAR(n) (variable up to n), INTEGER, REAL, BOOLEAN, DATE (YYYY-MM-DD), TIME (HH:MM:SS) DML — Data Manipulation Language (query and modify data): Querying: • SELECT col1, col2 FROM table — retrieve data • WHERE condition — filter rows • ORDER BY col ASC/DESC — sort results • GROUP BY col — group rows with same values • INNER JOIN table2 ON t1.col = t2.col — combine matching rows from two tables Aggregate functions: SUM(), COUNT(), AVG() Modifying: • INSERT INTO table VALUES (...) • UPDATE table SET col = value WHERE condition • DELETE FROM table WHERE condition SQL Script: A saved file of SQL commands that can be reused.

AS CS Long Answer Questions (Revision) #1 Flashcards

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