Databases Flashcards
Flat File definition
A database that consists of a single file.
Primary Key:
An attribute that is a unique identifier as its value will always be different depending on the object.
Foreign Key:
An attribute that links 2 tables together
Secondary Key:
Similar to a primary key but for humans to search quickly
Composite Key:
A key formed through combining multiple attributes
1NF:
+ Each field should be unique
+All data types in a field should be seperate (from the same domain)
+Values in fields should be atomic (only 1)
+No 2 records (whole records) should be identical
+ Each table needs a primary key
2NF:
1NF + No partial dependencies (for composite primary keys only)
3NF:
Contains no non-key dependencies, each field only depends on the primary key and nothing else
How to fix a M-M relationship?
Create a new table linking both with both tables primary keys as a composite primary key.
Indexing:
A method used to store the position of each record by a certain attribute, automatically done on the primary key, secondary keys are indexed as well
Data capture methods:
Magnetic Ink Character Recognition
Optical Mark Recognition (Multiple choice questions)
Optical Character Recognition
What is a Transaction
A transaction is a single operation executed on data
What is ACID:
Atomicity: A transaction must be finished or not at all
Consistency: A transaction must maintain the referential integrity rules between linked tables
Isolation: Simultaneous executions of transactions should lead to the same result as if they were executed one after another
Durability: Once a transaction has been executed, it will remain so regardless of anything
Name of the process of preventing simultaneous access to records, when one person is editing a database, another cannot
Record Locking
What is deadlock
When 2 users accessing different databases cannot switch to each others databases as record locking prevents it
