Presentation on theme: "Normal Forms By Christopher Archibald October 16 th 2007."— Presentation transcript:
Normal Forms By Christopher Archibald October 16 th 2007
Overview Database Normalization 1 st Normal Form 2 nd Normal Form 3 rd Normal Form Boyce- Codd Normal Form (BCNF) Lossless-Join
Normalization Normalization is a technique for designing relational table to: Minimize duplication of information Minimize duplication of information Reduce the potential for data anomalies Reduce the potential for data anomalies
Normal Form Normal forms provide a stepwise progression toward the goal of fully normalized relation schema that are free for data redundancies.
First Normal Form (1NF) 1NF definition: A schema R is in 1NF only when the attributes comprising the schema are atomic and single-valued No Multi-valued attributes No Multi-valued attributes No composite attributes No composite attributes No repeating groups (2 columns can not store similar information) No repeating groups (2 columns can not store similar information) Can’t have a Null Attribute Can’t have a Null Attribute Must have a Primary Key Must have a Primary Key
First Normal Form Example This is in 1NF (Has primary Key, no repeating group, No Null attributes and No multivariable What happens if James gets a Second Phone Number?
First Normal Form Example No longer in 1NF because Telephone Number has a multivariable. Now we need to redesign our table
First Normal Form Example Not in First Normal forum Tel. No. 3 is a null attribute Tel. No. 1-2 repeat similar information (Repeating group)
First Normal Form This is in First Normal Form Telephone Number is no long a repeating group No Multivariable No Null Attributes Has a Primary Key
Second Normal Form (2NF) 2NF Definition: A relation schema R is in 2NF if every non-prime attribute in R is fully functionally dependent on the primary key of R. Must be 1NF Must be 1NF An Attribute that is not part of the candidate key must be dependent on the candidate key and not a part of the candidate key An Attribute that is not part of the candidate key must be dependent on the candidate key and not a part of the candidate key
Second Normal Form Example Only Candidate key is (Employee, Skill) Not in 2NF Current Work Location is dependent on Employee Can Cause an Anomaly Updating Jones Work location for Typing and Shorthand but not Whittling. Then asking “What is Jones current work location”, can cause a contradictory answer, because there are 2 different locations.
Second Normal Form Example Both tables are in 2NF Meets 1NF requirements No non-primary key attribute is dependent on part of a key.
1NF and 2NF 1NF and 2NF remove most anomalies Following table is in 2NF There is redundancy under Winner/Winner DoB Al Fredrickson and Chip Masterson Al Fredrickson and Chip Masterson Can cause an anomaly Can cause an anomaly
Third Normal Form (3NF) 3NF Definition: A relation schema R is in 3NF if no non-prime attribute is functionally dependent on another non- prime attribute in R Table must be in 2NF Table must be in 2NF Eliminate field that do not depended on the primary key by placing them in different tables Eliminate field that do not depended on the primary key by placing them in different tables
Third Normal Form Example Table is in 2NF but fails to meet 3NF Winner Date of Birth is Dependent on Winner If Al Fredrickson Date of birth is update in the first row but not the second ask, “What Al Fredrickson Date of birth” will result in 2 different dates. If Al Fredrickson Date of birth is update in the first row but not the second ask, “What Al Fredrickson Date of birth” will result in 2 different dates.
Third Normal Form Example Table is in 3NF Meets 1NF and 2NF No non-primary Key attribute is Dependent on another non- primary Key attribute Update Anomalies cannot occur in these tables
Boyce-Codd Normal Form (BCNF) BCNF Definition: A relation Schema R is in BCNF if for every non-trivial functional dependency in R, the determinant is a superkey of R Does not allow Functional Dependency that is not part of a Candidate key Does not allow Functional Dependency that is not part of a Candidate key Most 3NF meet the requirement of a BCNF
Boyce-Codd Normal Form Example Candidate key (Tutor ID, Student ID) And (SSN, Student ID) Table is in 3NF, but not BCNF SNN is dependent on Tutor ID but (Tutor id, SNN) is not a Candidate key
Other Normal Forms There is also Fourth normal form Fourth normal form Fifth normal Form Fifth normal Form Domain/key Normal form Domain/key Normal form Sixth normal form Sixth normal form Which will be covered in chapter 9
Lossless-Join Decomposition The principle behind Lossless-Join decomposition is that the decomposition of a relation schema, R, should be strictly reversible, i.e. When we break tuples in to different tables for normalization we should be able to combined them and get what we started
Lossless-Join Decomposition Flight # OriginDestinationMileage DL723Boston St. Louis 1214 DL577Denver Los Angeles 1100 DL5219Minneapolis St. Louis 580 DL357ChicagoDallas1058 DL555DenverHouston1100 DL5237Cleveland 580
Lossless-Join Decomposition OriginDestinationMileage Boston St. Louis 1214 Denver Los Angeles 1100 Minneapolis St. Louis 580 ChicagoDallas1058 DenverHouston1100 Cleveland 580 Flight # MileageDL7231214 DL5771100 DL5219580 DL3571058 DL5551100 DL5237580
Lossless-Join Decomposition Flight # OriginDestinationMileage DL723Boston St. Louis 1214 DL577Denver Los Angeles 1100 DL577DenverHouston1100 DL5219Minneapolis St. Louis 580 DL5219Cleveland 580 DL357ChicagoDallas1058 DL555Denver Lost Angeles 1100 DL555DenverHouston1100 DL5237Minneapolis St. Louis 580 DL5237Cleveland 580