Unit 4 Exchanging Data Flashcards
What are the types of Compression?
- Lossy
- Lossless
What is Lossy Compression?
Removing non-essential data
What is Lossless Compression?
Summarizing patterns in the data without permanently removing any data
What is Run Length Encoding?
A basic method of coding that summarizes consecutive patterns of the same data
What does RLE work best on?
Image and sound data
What is Dictionary Compression?
Spots regularly occurring data and stores it separately in a dictionary
How many bits is an ASCII character?
8
What is Encryption?
A way of making sure that data cant be read without a way to decrypt it
What is the Caesar Cypher?
A type of encryption where letters of the alphabet are shifted by a constant amount
What is a Brute Force Attack?
A method that attempts to apply every possible key to decrypt ciphertext until one works
What is Frequency Analysis?
A method that looks at the most frequent characters in cypher text and comparing them to regular text
What is the Vernam Cypher?
A type of encryption, also know as the one-time pad. It is the only cypher text that is proven to be unbreakable
What are the features of a Vernam Cypher key? (5)
- Must be truly random
- Must be greater or equal to the length of the plaintext
- Must only be used once
- Must be shared by hand separate to the original message
- Must be destroyed immediately after use
What is Symmetric Encryption?
Also known as private key encryption, the same key is used to encrypt and decrypt
What is Asymmetric Encryption?
A type of encryption that uses 2 keys. One key (public key) is made public so that others can encrypt data before sending it to you. Another key (private key) is only known to you and can be used to decrypt the data
What is Hashing?
A type of encryption that is one-way and cannot go back to the original. Useful for storing encrypted PINs
What is the simplest kind of Database?
A flat file consisting of information about a single entity
What is an Entity?
A category of object, person, event or thing of interest about which data needs to be recorded
What is an Entity Identifier?
A name which uniquely identifies a particular record (also known as primary key)
What is a Composite Primary Key?
Where 2 or more attributes are needed to uniquely define a record
What are the Entity Relationships? (3)
- One to one
- One to many
- Many to many
What is a Foreign Key?
An attribute that creates a join between 2 tables (relations)
What is Referential Integrity?
Where no foreign key can reference a record that doesn’t exist in another table
Can a many to many relationship be directly linked?
No, an extra table is required
What is a Relational Database design? (5)
- Data is held in tables called relations
- One row holds one record
- Each column represents one attribute
- Each relation holds data about a single entity
- A database has one or more relations
What is Normalization?
A process used to come up with the best possible design for a database where tables should be organized so data is not duplicated in the same table or different tables
What is First Normal Form?
Contains no repeating attributes or groups of attributes
What is Second Normal Form?
Contains no partial dependancies
What is Third Normal Form?
No non-key dependencies
What type of language is SQL?
Declarative
What does the SELECT statement do?
Used to extract fields from one or more tables
What is the order of the SELECT statement? (4)
- SELECT
- FROM
- WHERE
- ORDER BY
What does the ORDER BY statement do?
Sorts the results of an SQL query. Can be ASC or DESC
e.g
ORDER BY Price DESC, productName ASC
What does * mean in SQL?
All or one or many characters
What does the LIKE statement do?
Searches for a pattern
e.g
WHERE subject LIKE “Comp*”
What does the BETWEEN statement do?
Selects between a specified range
How is the CREATE TABLE statement used?
Must state the name of the table and the limits of each attribute
e.g
CREATE TABLE tblProduct
(
ProductID CHAR(4) NOT NULL PRIMARY KEY,
Description VARCHAR(20) NOT NULL,
Price CURRENCY
)
What is the CHAR(n) data type?
Character string or fixed length n
What is the VARCHAR(n) data type
Character string variable length, max n
What is the BOOLEAN data type?
True or false
What is the INTEGER,INT data type?
Integer
What is the FLOAT data type?
Number with a floating decimal point
What is the DATE data type?
Day, month, year values
What is the TIME data type?
Hour, minute, second values
What is the CURRENCY data type?
Formats numbers in the currency used in your region
What does the ALTER TABLE statement do?
Add, deletes or modifies columns in an existing table
e.g
ALTER TABLE tblProduct
ADD QtyInStock INTEGER
or
DROP QtyInStock
or
MODIFY COLUMN Description VARCHAR (30) NOT NULL
What does the INSERT INTO statement do?
Inserts a new record into a table
e.g
INSERT INTO Product (ProductID, Description, Price),
VALUES (“A345”, “Pink Rabbit”, 7.50)
What does the UPDATE statement do?
Updates a record in a table
e.g
INSERT INTO Product (ProductID, Description, Price),
VALUES (“A345”, “Pink Rabbit”, 7.50)
What does the DELETE statement do?
Deletes a record in a table
e.g
DELETE FROM Product
WHERE ProductID = “A345”
What is EDI?
Electronic Data Interchange
The computer-to-computer exchange of documents such as purchase orders, invoices and shipping documents. All documents must be a standard format s o the EDI translator can understand them
What does ACID stand for? (4)
- Atomicity
- Consistency
- Isolation
- Durability
What is Atomicity in ACID?
Requires that a transaction is completed fully or not at all
What is Consistency in ACID?
Requires that every transaction meets the defined guidelines
What is Isolation in ACID?
Requires that transactions done at the same time have the same result as if they were done one after the other
What is Durability in ACID?
Requires that once a transaction has been completed it stays that way even in a power cut
What is a problem with a Multi-User Database?
Allowing multiple users to simultaneously access a database could potentially cause one of the updates to be lost
What is Record Locking and what does it prevent?
It prevents updates being lost or inconsistencies by locking access to objects that are being modified
What is Deadlock?
A problem that occurs when two users are trying to update two records and neither can proceed
What are the 2 types of Serialization?
Timestamp ordering, Commitment ordering
What does Serialization do?
Makes sure that transactions do not overlap in time and therefore cannot interfere with each other or lead to updates being lost
What is Timestamp Ordering?
Every object in the database has a read timestamp and a write timestamp. When a user tries to save an update, if the read timestamp is not the same as it was when they started the transaction, the DBMS knows another user has accessed the same object
What is Commitment Ordering?
Transactions are ordered in terms of their dependencies on one another as well as the time they were initiated
What is Redundancy?
Duplicate hardware, located in different geographical areas, mirrors every transaction that takes place on the main system. If the main system fails, this takes over
