AS Level CS (9618) 8 Database

Database

A structured collection of items of data that can be accessed by different applications programs.

Relational database

a database where the data items are linked by internal pointers.

Table

a group of similar data in a database with rows for each instance of an entity and columns for each attribute.

Record (database)

a row in a table in a database.

Field

a column in a table in a database.

Tuple

one instance of an entity which is represented by a row in a table.

Entity

anything that can have data stored about it; for example a person; place; event; things

Attribute (database)

an individual data item stored for an entity; for example a person; attributes could include name; address; date of birth

Candidate key

an attribute or smallest set of attributes in a table where no tuple has the same value

Primary key

a unique identifier for a table. It is a special case of a candidate key

Secondary key

a candidate key that is an alternative to the primary key

Foreign key

a set of attributes in one table that refer to the primary key in another table

Relationship

situation in which one table in a database has a foreign key that refers to a primary key in another table in the database

Referential integrity

property of a database that does not contain any values of a foreign key that are not matched to the corresponding primary key

Index (database)

a data structure built from one or more columns in a database table to speed up searching for data

Entity-relationship (E-R) model or E-R diagram

a graphical representation of a database and the relationships between the entities

Normalisation (database)

the process of organising data to be stored in a database into two or more tables and relationships between the tables; so that data redundancy is minimised

First normal form (1NF)

the status of a relational database in which entities do not contain repeated groups of attributes

Second normal form (2NF)

the status of a relational database in which entities are in 1NF and any non-key attributes depend upon the primary key

Third normal form (3NF)

the status of a relational database in which entities are in 2NF and all non-key attributes are independent

Composite key

a set of attributes that form a primary key to provide a unique identifier for a table

Database management system (DBMS)

systems software for the definition and creation and manipulation of a database

Data management

the organisation and maintenance of data in a database to provide the information required

Data dictionary

a set of data that contains metadata (data about other data) for a database

Data modelling

the analysis and definition of the data structures required in a database and to produce a data model

Logical schema

a data model for a specific database that is independent of the DBMS used to build that database

Access rights (database)

the permissions given to database users to access modify or delete data

Data definition language (DDL)

a language used to create modify and remove the data structures that form a database

Data manipulation language (DML)

a language used to add modify delete and retrieve the data stored in a relational database

SQL script

a list of SQL commands that perform a given task often stored in a file for reuse