GCSE A* REVISION NOTES


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Databases

Database Concept

describe a database as a persistent organised store of data

Database – A persistent and organised store of data

explain the use of data handling software to create, maintain and interrogate a database.

Data handling software helps users to create, maintain and interrogate a database

DBMS

describe how a DBMS allows the separation of data from applications and why this is desirable

DBMS – Database Management System

describe the principal features of a DBMS and how they can be used to create customised data handling applications.

Relational Databases

understand the relationship between entities and tables

Entity – A real world item about which data is stored in a database. Corresponds to tables in the database

understand the components of a relational database, such as tables, forms, queries, reports and modules

understand the use of logical operators in framing database queries

explain the use of key fields to connect tables and avoid data redundancy

Primary Key – Field that holds data unique for each record (unique identifier). Two records cannot have the same primary key but can have duplicated data for other fields

Foreign Key – Primary key from another table linking the two. This means data relating to the record in this table can be retrieved from the table with the foreign key with no duplication of data. Preventing data redundancy.

describe methods of validating data as it is input

Check Digit – A calculation is performed on a number that generates another digits which is appended to the number. This is common on account numbers, bar codes and book ISBNs. When the data is entered the calculation is repeated and if the same check digit is not generated the input is rejected.

Format Check- Data must comfort to a particular pattern such as registration plate

Length check – Data must be within certain limits. Telephone number might be set up to be no longer than 12 digits

Lookup check – Checks that the entered data exists in a database

Presence check – Checks that something has been entered

Range check – Checks data is within a given sensible range

Type Check – Checks that the data entered is the correct type


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