Topic 3: Exchanging Data Flashcards
What is Normalisation
- The process of designing a relational database.
- Aims to produce the best and most effective design
What are some considerations of normalisation
- Remove redundant or duplicated components.
- Ensure data in linked tables is consistent.
- Allow complex queries to be carried out.
- Ensure records can be added or removed without problems.
What is first normal form
Attributes may contain a single value only
What is second normal form
- In First Normal Form.
- Partial dependencies are not allowed.
What is Third Normal Form
- In Second Normal Form.
- Non key dependencies are not allowed.
What is Run Length Encoding
- A lossless compression method.
- Repeated values are replaced with a single instance of the value and the number of times the value occurs.
- It relies on all consecutive pieces of data being the same.
- It offers poor reduction in file size if there is little repetition.
What is Indexing
- Stores the position of each record when records are ordered by a certain attribute.
- The primary key is automatically indexed.
- Allows data to be found and accessed quickly
Ways of Capturing Data
- There are many ways to capture the data needed for a database.
- The most appropriate way will depend on the type and quantity of data needed and available resources.
- Data may be manually entered by a human or scanned in using optical character recognition, sensors or barcodes.
What are the 3 types of Entity Relationship Modelling
One - One
One - Many
Many - Many
What is One - One ERM
Each Entity can be associated with one other entity only
What is One - Many ERM
A single record can be associated with many records in another table
What is Many - Many ERM
Each record in one entity can be associated with multiple records in another entity, and vice versa
What is SQL used for
To sort, structure and filter the data
What is Referential Integrity
- Ensures consistency.
- Ensures that information is not removed if it is needed elsewhere in the database.
What is Transaction Processing
- A single operation executed on data.
- Must be processed in line with ACID
What is ACID
Atomicity
Consistency
Isolation
Durability
What is Atomicity
The whole transaction must be processed
What is Consistency
Transactions must maintain the referential integrity rules between linked tables
What is Isolation
Executing transactions at the same time must produce the same result as if they were executed one after the other.
What is Durability
When a transaction has been executed it will not be undone
What is Record Locking
- Prevents records being accessed by more than one transaction at the same time.
- Prevents inconsistencies and data loss.
- Can result in deadlock.
What is a Redundancy
- Multiple copies of the data are kept in different physical locations.
- If data in one copy is lost or damaged it can be retrieved from another copy.
What are the 3 main SQL commands
SELECT
FROM
WHERE
What does LIKE mean in SQL
Used to specify wildcard criteria in conjunction with the % character
e.g. Searching for records that contain a specific word pattern
What does JOIN do in SQL
Allows rows from multiple tables to be returned
and defines how the tables are linked.
What does INSERT INTO do in SQL
Inserts a new record into an existing table
What does DELETE do in SQL
Deletes a record from a table
What does DROP do in SQL
Deletes an Entire table
What is an Entity
An entity is item about which information is stored such as books, or customers
What is an Attribute
Attributes are the categories in which data is collected such as height or name
What is a Flat File Database
- Consists of a single file.
- Usually based around a single entity.
- Only one table.
What is a Relational Database
- Uses many tables to store data about different entities.
- These tables are linked together.
What is a Primary Key
- A unique identifier, different for each object in the database
- Usually and ID number or other unique ID
What is a Foreign Key
- Used to link two tables together.
- The primary key from a different table.
What is a Secondary Key
- Used to enable searching or sorting.
- Usually a common field like name.
What is Dictionary Encoding
- A lossy compression method.
- Commonly used data is replaced with an index.
- The compressed data is stored with a dictionary.
- The dictionary can restore original data.
- The dictionary links the commonly used data to the index.
What is Hashing
- Turns an input into a value of a fixed size.
- The input is known as a key.
- The output is known as a hash.
- The hash cannot be turned into the key.
- A hash table stores keys and their matching values.
- They can be used to lookup data in an array.
What makes a Good Hash Function
- Quick to run
- Low Rate of Collisions
What helps overcome collisions in Hashing
Using a second hash function and storing items together with the hash
What is Encryption
- Used to keep data secure.
- Used when transmitting or storing data in ways where others may have access to it.
- Scrambles the data to prevent it being easily read.
- Encryption keys are used to encrypt and decrypt data.
What is Symmetric Encryption
- The same private key is used by the sender and receiver.
- The same key is used to encrypt and decrypt data.
- A key exchange process is used to share the key.
- Data can be read should the key be intercepted.
What is Asymmetric Encryption
- Uses two different keys.
- The public key is used to decrypt data and can be shared anywhere.
- The private key is used to encrypt data and must be kept securely.
- The two keys are known as a key pair and are related to each other.
- Encrypting a message using the public key verifies that it was sent and encrypted by the owner of the key.
What are Search Engines
- Search a database of web addresses to find resources based on criteria set by the user.
- Rely on an index of pages through which they search.
- Web Crawlers build the index by traversing the Internet exploring all links on the page.
- Crawlers collect keywords, phrases and metadata from pages.
Name 3 Network Topologies
- Bus
- Star
- Mesh
Describe a Bus Network
All devices are connected to a single cable (called the bus) A terminator is at each end of the cable.
Describe a Star Network
All nodes are connected to one or more central switches. Often used with wireless networks.
Describe a Mesh network
No central connection point, with each device connecting directly to others. Full mesh networks have every device connected to every other device. Partial mesh networks have each device connected to several others but not necessarily every other device.
Adv/Disadvantages of a Bus Network
ADV
▪ Easy to install extra devices.
▪ Cheap to install as it doesn’t require much cable.
DIS
▪ If the cable fails or is damaged the whole network will fail.
▪ Performance becomes slower as additional devices are connected due to data collisions.
▪ Each device receives all data, a security risk
Adv/Disadvantages of a Star Network
ADV
▪ Every device has its own connection so failure of one node will not affect others.
▪ New devices can be added by simply connecting them to the switch.
▪ Usually have higher performance as a message is passed only to its intended recipient.
DIS
▪ If the switch fails it takes out the whole network.
▪ Requires a lot of cable so can be expensive.
Adv/Disadvantages of a Mesh Network
ADV
▪ Messages can be received more quickly.
▪ Messages have many possible routes they can take.
▪ Multiple connections mean that no device should be isolated
▪ Each device can talk to more than one node at the same time.
▪ Devices can be added without interruption.
DIS
▪ Can be impractical and expensive to setup.
▪ Require a lot of maintenance.
What is a Topology
- The physical topology defines the physical layout of the network
- The logical topology defines the way data flows through the network
What is a Protocol
A set of rules for communication between devices
What is a Network
Two or more computers connected together for the purposes of transmitting data
What’s a LAN
Local Area Network
Covers a small geographical area
What’s a WAN
Wide Area Network
Covers a Large Geographical area
What is the TCP/IP stack
- Transfer Control Protocol / Internet Protocol.
- A group (stack) of protocols which work together.
- Controls the flow of data packets through the network.
What are the 4 Layers of the TCP/IP Stack
- Application
- Transport
- Network
- Link
What’s the DNS
- Domain Name System
- Allows websites and other network devices to be identified by a human readable name.
- DNS Server converts the name to an IP Address.
- A hierarchy.
- Each domain name is separated by a dot.
- The names to the right are highest in the hierarchy.
What is the Application Layer
- Top of the stack.
- Specifies the required protocol needed by the application the user is using
What is the Transport Layer
- Uses TCP to establish a connection through the network between the source and recipient devices.
- Splits data into packets labelled with a packet number.
- Requests retransmission of any packets lost during transit.
What is the Network Layer
- Adds a source and destination IP Address to packets.
- Routers use this address to forward packets through the network to their destination.
What is the Link Layer
- The physical connection between devices.
- Uses a MAC Address to communicate.
What is a Client Server Network
- Clients connect to a central server.
- The server is a powerful computer central to the network.
- It holds all the data.
- More secure setup.
- Clients do not need to be backed up.
- Data and resources can be shared easily.
- Expensive to setup.
- More secure.
What’s a Peer to Peer Network
- Computers are connected directly to each other.
- Computers share data with one another.
- Quick, cheap and easy to setup.
- Less secure.
- Easier to maintain.
What is a Proxy Server
- Sits between a user and the resource they are accessing.
- Protects users’ privacy.
- Caches frequently accessed websites to increase performance.
- Reduces web traffic.
- Uses rules to block access to sensitive information.
What does the Page Rank Algorithm do
- Ranks each web page
- Higher ranked pages appear first when results are shown.
- Rank based on the number of incoming links on the page and the rank of these pages.
- This is stored in a directed graph.
- The sites are nodes and the links between the pages are the arcs.
What’s the Algorithm of the Page Rank Algorithm
PageRank(x) = (1-d) + d[(PageRank(T1) ÷ Count(T1)) + … + (PageRank(Tn) ÷ Count(Tn)
What are the 2 types of Compression
Lossy
Lossless
What is Compression
Reduces the space needed to store or transmit a file.
Why is Compression Important
Important when sharing files over a network or The Internet and when dealing with limited storage space.
Increases the number of files which can be sent or received.
What is Lossy Compression
Lossy compression removes some information whilst compressing the file. Original cannot be retrieved.
What is Lossless Compression
Lossless compression reduces the size of the file without losing any information.
Original can be retrieved.
Name 5 pieces of Network Hardware
- NIC
- Switches
- WAPs
- Routers
- Gateway
What is an NIC
Network Interface Card
* May be wired or wireless.
* Allows a device to connect to a network.
* Has a unique MAC (Media Access Control) address assigned to it
What is a Switch
- Controls the flow of data through the network.
- Used in star topologies.
What is a WAP
Wireless Access Point
* Allows devices to connect wirelessly to a network.
* Used in mesh networks.
* Often used with a router to allow devices Internet access.
What is a Router
- Used to connect two or more networks together.
- Often used between a home/office network and an ISP to allow Internet access.
What is a Gateway
- Used to connect networks using different protocols.
- Translates protocols to allow devices to communicate.
- Changes the packet headers.
What is Packet Switching
- Data is split into packets.
- Packets are sent across the network.
- Packets may take different routes through the network.
What is Circuit Switching
- A direct link is created between devices.
- The link is maintained for the entire conversation.
- Both devices must transfer data at the same rate.
What is a Firewall
- Prevent unauthorised access to the network.
- Has two NICs.
- Data enters one NIC and is compared to a set of rules.
- Traffic which matches the rules is passed out the other NIC.
What is Server Side Processing
- Client sends all data to the server for processing. Examples include SQL and PHP.
- It requires no plugins on the client.
- Servers can usually perform large or complex calculations more quickly.
- It is not browser dependent.
- It is more secure
What is Client Side Processing
- Client processes the data locally.
- Examples include JavaScript.
- Web pages can immediately respond to actions.
- Code executes more quickly.
- It gives more control over the behaviour and look of websites.
