Rule

Description

Representation of information

All data must be represented logically in tables

Guaranteed logical accessibility

All data is accessible logically using a combination of table name, key name, key value and column.

NULL support

Null value represents missing information and are not to be confused with empty, blank or zero filled data. They also are not necessarily equal.

Dynamic online catalog

The definition of data is represented in the same manner as data so that it can be relationally accessed. Example every database has catalog tables

Comprehensive data sub-language (high level language example SQL )

A unique language which is supported along with several other programming languages to achieve data definition, view and manipulation.

Updatable views

All views that can theoretically exists can be updated.

High level insert, updates and delete

Both base and derived relations can be handled as singular requests and apply to retrieval, insert, update and deletion of data.

Physical data independence

Program and terminal activities are preserved when changes are made in storage representation or access methods.

Logical data independence

Program and terminal activities are preserved when changes are made to base tables.

Integrity independence

Integrity constraints must be definable in the unique sub-language and stored in the catalog.

Distribution independence

The unique sub-language must support database distribution while preserving program and terminal activities.

Nonsubersion

A relational system which perform low-level processing of records cannot supplant the integrity rules in effect in high level, record processing by a relational language.

Relational Table database

Defined as a rectangular array of columns and rows where columns are homogenous, non-grouped, uniquely named data items( attributes ) and rows are not duplicated. It is also important to impose the property that column and row order within the array is immaterial.