17.1 Notation and Normalization (Revision #13)

Notation - IE

Aqua Data Studio's ER Modeler uses the Information Engineering Notation (IE) for Data Modeling. Information Engineering serves many purposes, including organisation planning, business re-engineering, application development, information systems planning and systems re-engineering.

Normalization

First Normal Form

An entity is in the first normal form (1NF) if it contains no repeating groups.

Second Normal Form

An entity is in the second normal form (2NF) if all of its attributes depend on the whole (primary) key.

Third Normal Form

An entity is in the third normal form (3NF) if it is in the second normal form and all of its attributes are not transitively dependent on the primary key. The third normal form means that no column within a table is dependent on a descriptor column that, in turn, depends on the primary key.

If you cannot find a place for an attribute that observes these rules, you have probably made one of the following errors:

• The attribute is not well defined.
• The attribute is derived, not direct.
• The attribute is really an entity or a relationship.
• Some entity or relationship is missing from the model.

Boyce - Codd Normal Form (BCNF)

Boyce-Codd Normal Form (BCNF) is an extension of 3NF in the case with two or more candidate keys which are composite and overlapping (that is, they have at least one field in common). If these conditions are not fulfilled, 3NF and BCNF are equivalent. A table is BCNF if, and only if its only determinants are candidate keys.

Fourth Normal Form

A table is in Fourth Normal Form (4NF) if it is 3NF and it does not represent two or more independent many-to-many relationships.

Fifth Normal Form

A table is in Fifth Normal Form (5NF) if it is 4NF and its information content cannot be reconstructed from several tables containing fewer attributes.

Relationships

One-to-One Relationship

A pair of tables bears a one-to-one relationship when a single record in the first table is related to only one record in the second table.

One-to-Many Relationship

A pair of tables bears a one-to-many relationship when a single record in the first table is related to one or more records in the second table. A single record in the second table is related to only one record in the first table.

Many-to-Many Relationship

A pair of tables bears a one-to-one relationship when a single record in the first table can be related to one or more records in the second table. A single record in the second table can related to one or more records in the first table.