Database Normalization Il-Han Yoo CS 157A Professor: Sin-Min Lee

 Database normalization relates to the level of redundancy in a relational database’s structure.  The key idea is to reduce the chance of having multiple different version of the same data.  Well-normalized databases have a schema that reflects the true dependencies between tracked quantities.  Any increase in normalization generally involves splitting existing tables into multiple ones, which must be re-joined each time a query is issued. Database Normalization

Normal Forms Edgar F. Codd originally established three normal forms: 1NF, 2NF and 3NF. Edgar F. Codd originally established three normal forms: 1NF, 2NF and 3NF. 3NF is widely considered to be sufficient. 3NF is widely considered to be sufficient. Normalizing beyond 3NF can be tricky with current SQL technology as of 2005 Normalizing beyond 3NF can be tricky with current SQL technology as of 2005 Full normalization is considered a good exercise to help discover all potential internal database consistency problems. Full normalization is considered a good exercise to help discover all potential internal database consistency problems.

First Normal Form ( 1NF ) “What is your favorite color?” “What food will you not eat?” TABLE 1 Person / Favorite Color Bob / blue Jane / green TABLE 2 Person / Foods Not Eaten Bob / okra Bob / brussel sprouts Jane / peas

Second normal Form ( 2NF ) 2NF prescribes full functional dependency on the primary key. 2NF prescribes full functional dependency on the primary key. It most commonly applies to tables that have composite primary keys, where two or more attributes comprise the primary key. It most commonly applies to tables that have composite primary keys, where two or more attributes comprise the primary key. It requires that there are no non-trivial functional dependencies of a non-key attribute on a part (subset) of a candidate key. A table is said to be in the 2NF if and only if it is in the 1NF and every non- key attribute is irreducibly dependent on the primary key It requires that there are no non-trivial functional dependencies of a non-key attribute on a part (subset) of a candidate key. A table is said to be in the 2NF if and only if it is in the 1NF and every non- key attribute is irreducibly dependent on the primary key

2NF Example PART_NUMBER (PRIMARY KEY) SUPPLIER_NAME (PRIMARY KEY) PRICE SUPPLIER_ADDRESS The PART_NUMBER and SUPPLIER_NAME form the composite primary key. SUPPLIER_ADDRESS is only dependent on the SUPPLIER_NAME, and therefore this table breaks 2NF.

SUPPLIER_NAME (PRIMARY KEY) SUPPLIER_ADDRESS 2NF Example (Con’t) In order to find if a table is in 2NF, ask whether any of the non-key attributes of the table could be derived from a subset of the composite key, rather than the whole composite key. If the answer is yes, it's not in 2NF. This is solved sometimes by using a correlation file, such as the supplier table above.

Third normal form 3NF requires that there are no non-trivial functional dependencies of non-key attributes on something other than a superset of a candidate key. A table is in 3NF if none of the non-primary key attributes is a fact about any other non-primary key attribute. In summary, all non-key attributes are mutually independent.

3NF Example PART_NUMBER (PRIMARY KEY) MANUFACTURER_NAME MANUFACTURER_ADDRESS MANUFACTURER_NAME (PRIMARY KEY) MANUFACTURER_ADDRESS PART_NUMBER (PRIMARY KEY) MANUFACTURER_NAME

Example Problems ? 1.Not very efficient with storage 2.This design does not protect data integrity 3.This table does not scale well

First Normal Form

Defining Relationships One to One One to Many Many to Many

Second Normal Form

Third Normal Form This new table violate Second Normal Form as the street and city will be verically redundant. Province will need to be in its own table which the city table will refer to as a foreign key.

Boyce-Codd normal form (BCNF) BCNF requires that there are no non-trivial functional dependencies of attributes on something other than a superset of a candidate key (called a superkey). All attributes are dependent on a key, a whole key and nothing but a key (excluding trivial dependencies, like A->A).

A table is said to be in the BCNF if and only if it is in the 3NF and every non-trivial, left- irreducible functional dependency has a candidate key as its determinant. In more informal terms, a table is in BCNF if it is in 3NF and the only determinants are the candidate keys.

Fourth normal form (4NF) 4NF requires that there are no non-trivial multi-valued dependencies of attribute sets on something else than a superset of a candidate key (called a superkey). 4NF requires that there are no non-trivial multi-valued dependencies of attribute sets on something else than a superset of a candidate key (called a superkey). A table is said to be in 4NF if and only if it is in the BCNF and multi-valued dependencies are functional dependencies. A table is said to be in 4NF if and only if it is in the BCNF and multi-valued dependencies are functional dependencies.

4NF Example EMPLOYEE_IDQUALIFICATION_IDTRAINING_COURSE_ID employee_qualification table: EMPLOYEE_ID QUALIFICATION_ID employee_training_course table: EMPLOYEE_ID TRAINING_COURSE_ID

EMPLOYEE_IDDEGREE_IDUNIVERSITY_ID 4NF Expample (con’t) This would require no changes to fit the fourth normal form requirements.

Fifth normal form (5NF and also PJ/NF) 5NF requires that there are no non-trivial join dependencies that not follow from the key constraints. 5NF requires that there are no non-trivial join dependencies that not follow from the key constraints. A table is said to be in the 5NF if and only if it is in 4NF and every join dependency in it is implied by the candidate keys. A table is said to be in the 5NF if and only if it is in 4NF and every join dependency in it is implied by the candidate keys.

Domain/key normal form(DKNF) DKNF requires that each key uniquely identifies each row in a table. DKNF requires that each key uniquely identifies each row in a table. A domain is the set of permissible values for an attribute. A domain is the set of permissible values for an attribute. By enforcing key and domain restrictions, the database is assured of being freed from modification anomalies. By enforcing key and domain restrictions, the database is assured of being freed from modification anomalies.

While sometimes called the 6NF, the DKNF should not be considered together with the seven other normal forms (1–6 and Boyce-Codd), because contrary to them it is not always achievable; furthermore, tables in the real 6NF are not always in the DKNF. While sometimes called the 6NF, the DKNF should not be considered together with the seven other normal forms (1–6 and Boyce-Codd), because contrary to them it is not always achievable; furthermore, tables in the real 6NF are not always in the DKNF.

Sixth normal form(6NF) This normal form was, as of 2005, only recently conjectured: the sixth normal form (6NF) was only defined when extending the relational model to take into account the temporal dimension (ie. time). This normal form was, as of 2005, only recently conjectured: the sixth normal form (6NF) was only defined when extending the relational model to take into account the temporal dimension (ie. time). Unfortunately, most current SQL technologies as of 2005 do not take into account this work, and most temporal extensions to SQL are not relational. Unfortunately, most current SQL technologies as of 2005 do not take into account this work, and most temporal extensions to SQL are not relational.