SLR 10 Flashcards
Databases
What does organising data in a database allow for?
Adding, Modification, Deletion, Searching
What are electronic databases good for?
Makes it easier to backup data and save copies
Can be accessed by multiple people at a time and from many different locations
How is data stored in a table
Entities/files are stored in records (rows/tuples) and fields (columns/attributes)
What is a flat tile database?
A simple representation of data on a table
Why are large flat tile databases inefficient?
If they end up too large they end up inefficient as they are waste space, making them slow and hard to maintain
What is a relational database?
A database which is split into multiple tables which are all linked together. There should be one common field in all tables for the link to work
What is a foreign key?
A column which is linked to another column in a linked table
What are the 3 types of relationships?
One-to-one
One-to-many
Many-to-many
How can a database be made useful?
Allowing it to query to quickly retrieve information
This is done by keeping an index of primary keys
What are the methods of capturing data?
Capturing
Selecting
Managing
Exchanging
What is a paper based form?
A physical sheet of paper you can write on, which can be scanned in order to collect data. This is done using Optical Character Recognition (OCR)
What is Optical Character Recognition (OCR)?
Scans an image for text symbols into a machine-readable format
What is Optical Mark Recognition (OMR)?
Used to scan multiple choice tests and lottery tickets, helping reduce human error
What is Structured Query Language (SQL) used for?
To retrieve data with the following commands:
SELECT
FROM
WHERE
It is developed with Query By Example (QBE) to create statements which are executed against the database to complete the above tasks
What can SQL AND QBE do?
Specify tables
Specify fields
Specify criteria
Specify output sorting
Using boolean expressions such as NOT, OR, NOT
How are tables modified?
Using Database Manipulation Language (DML) these can be used:
UPDATE
DELETE
INSERT
What does ADBMS do?
Prevents the creating of duplicate private keys
Enforcing validation rules
Provides secure access
Provides encryption
Provides program data independence
Manages multiple users
What is XML and JSON?
They are human-readable and are open formats for structuring data
They’re common standards for storing and transporting data
How can data be exchanged?
Memory strikes
Optical media
Removable hard disks
Emails
Paper based forms
What is an Electronic Data Interchange (EDI)
A protocol which faciliates the exchange of data
What are the 3 types of standard form?
1NF, 2NF, 3NF
What rules need to be followed to get 1NF?
- All field names must be unique
- Values in fields should be from the same domain
- Values in fields should be atomic
- No two records can be identical
- Each table needs a primary key
What rules need to be followed to get 2NF?
- The data is already in 1NF
- Any partial independencies must be removed
What is a partial independency?
Occurs when one primary key determines another attribute
What is a dependency?
When one field relies on another field
What rules are need to be followed to get 3NF?
- The data is in 2NF
- Any transitive dependencies must be removed
What is a non-dependency key?
A value of a field which requires the value of another field that isn’t a part of the primary key
To remove this, get rid of unnecessary data and fields
What is a transitive dependency?
When an unrelated column is dependent on another unrelated column
What does atomic mean in CS?
A single item of data
What does SQL let you do?
Query Data
Manipulate data
Define data
Control data access
What SQL commands must you know?
SELECT
FROM
WHERE
LIKE
AND
OR
DELETE
INSERT
DROP
JOIN
Look in notes for examples
What is data integrity and what is it needed for?
Keeping a database consistent
This is needed so the database is always updated for everybody who access is
Definition: “The maintenance and consistency of data in a data stored. The data must relfect the reality of what it represents”
What is transactional processing?
Any information processing that is divided into individual operations called transactions
Each transaction needs to be complete as for everybody else it’ll never be partially complete
What is CRUD?
The commands:
CREATE (INSERT/CREATE)
READ (SELECT)
UPDATE
DELETE
What ensures data integrity?
Atomicity
Consistency
Isolation
Durability
What does Atomicity mean?
Means a change to a database is either completely performed or not at all
What does Consistency mean?
Any change in a database must retain the overall state, so if someone sends another money, they lose it and the other gains it
What does Isolation mean?
Means a transaction can’t be interrupted by another interruption
The current data used in the transaction is made so it can’t be accessed
What does Durability mean?
Means any change made to a database can’t be lost due to a system failure.
This is done by writing the effect of a transaction onto a non-volatile secondary storage so it can never be lost
