Database Systems

Concepts on Database Systems / 222

Data

Raw, unprocessed facts and figures.

Information

Processed, organised and structured data in a context.

Database

Structured collection of data/ information

Features of Good Information

Timely, accurate and complete

Features of Data Storage Management

Visual storage, how it’s structured

Most important feature of DBMS

An integrated view of an organisation’s operations

Relational Data Model

Data stored in tables with relationships between them.

Relation

Table

Two important features of rows/tuples

The number of them is indefinite and each one will describe a single instance of data.

Tuple

Row

How are tuples usually written?

Attributes in parentheses, with commas separating them.

What is meant by Data type?

Attributes must have a data type, but these depend on the particular DBMS.

What are common ‘Data Types’ for attributes?

TEXT, INTEGER, REAL, DATE

What is a Schema?

A relation is described USING a schema, consisting of name of the relation and the set of attributes (with their data types).

What is a Relation Instance?

Not static —> tuple insertion/updates/deletion —> A set of tuples for a relation at a moment is an instance of that relation.

PK

Unique attribute for an entity / should not change or become null.