Attributes and Tables

Understanding Attributes

Attributes are the characteristics or properties that represents the objects within a system in a database.
These can take the form of several data types, including text strings, integers, decimal numbers, dates, and Booleans.
Each attribute in a database must have a unique name.
Attributes can allow or disallow null values.
These properties describe the features of the data that is being stored.
An attribute’s data type dictates what kind of data can be stored in that attribute.

A Primary Key is a specific form of attribute that uniquely identifies every record in a database table.
Primary keys must contain unique values, and cannot contain null values.
A table can have only one primary key.

In the context of databases, a table is a set of data elements organised using a model of vertical columns (which are identified by their name) and horizontal rows.
The cell is the intersection of the row and column.
A table has a specified number of columns, but can have any number of rows.
The term relation is used to refer to a table, as a table is fundamentally a mathematical relation.

Table relationships define how data in one table relates to data in another table.
Table relationships can be one-to-one, one-to-many, or many-to-many.

A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables.
It acts as a cross-reference between tables because the foreign key in one table is a primary key in another table.

Database normalisation is the process of structuring a relational database in accordance with a series of normal forms in order to reduce data redundancy and improve data integrity.
Normalisation involves decomposing a table into less redundant and smaller tables without losing information.
Defining foreign keys in the old table referencing the primary keys of the new ones.
The objective is to isolate data so that additions, deletions, and modifications of a field can be made in just one table and then propagated through the rest of the database via the defined foreign keys.