1.4.2 Databases (Chp 8)

A row

A column

An organised collection of data

A flat file is a database that consists of one entity. Will usually be based around a single table.

A relational database are two tables entities/ tables that are linked together by a common item of interest as the primary and foreign key.

Diagram that shows the relationship between 2 or more tables

one to one relationship

one to many

many to many

unique identifier for each record in the table. Allows each record to be uniquely identified.

allows database to be searched quickly. User is unlikely to remember the unique primary key, but will remember a certain field i.e. surname. This makes it possible for the user to search.

attribute that links 2+ tables together. It exists in one table as the primary key and in another table as the foreign key.

• method is dependent on the context • i.e. manually entered in surveys • Bank scans checks using Magnetic Ink Character Recognition • Optical Mark Recognition

• selecting the correct data is an important part of data processing. • This could involve only selecting data that fits a certain criteria. • Collected data can be managed using SQL to sort, restructure, and select certain sections.

a technique used to help reduce data duplication in databases. the process of coming up with the best possible layout for a relational database.

• no redundancy • consistent data throughout linked tables records can be removed and added without issues

• all field names are unique • all records are unique • each record has a primary key • the values in the fields are of the same domain/ type • each value is atomic

• that the database is in 1NF - remove any partial dependencies (split the table)

-that the database is already in 2NF -remove any transitive data (everything must depend in the primary key and the primary key only.) (create 1:M relationship - might need a linking table)

Databases can hold vast amount of info and often need to support multiple simultaneous users. Users can be given different access rights to a database. (User Access Levels) - All these different database queries result in multiple transactions taking place, often at the same time.

a transaction is defined as a single operation executed on data. Transactions must be processed in line with ACID.

Atomicity, Consistency , Isolation, Durability

a transaction must either be processed entirely or not at all.

A transaction must keep the referential integrity rules between linked tables. Will ensure that an illegal transaction will be rejected so that the integrity of the database is upheld.