Chapter 2. The Relational Model (cont.) IST2101

Review: Determinant vs. Candidate Key IST2102 DeterminantsCandidate Key (StudentID, CourseID) StudentID CourseID (StudentID, CourseID) In a relation, a candidate key must be a determinant In a relation, a determinant may not be a candidate key A relation is well-formed if and only if every determinant is a candidate key.

Normalization Process 1.Identify all the candidate keys of the relation. 2.Identify all the functional dependencies in the relation. 3.Examine the determinants of the functional dependencies. If any determinant is not a candidate key, the relation is not well formed. In this case: a.Place the columns of the functional dependency in a new relation of their own. b.Make the determinant of the functional dependency the primary key of the new relation. c.Leave a copy of the determinant as a foreign key in the original relation. d.Create a referential integrity constraint between the original relation and the new relation. 4.Repeat step 3 as many times as necessary until every determinant of every relation is a candidate key. IST2103

Normalization Process: Example 1: Step 1 IST2104 Step 1. Identify all the candidate keys of the relation. PrescriptionNumber

Normalization Process: Example 1: Step 2 IST2105 Step 2. Identify all the functional dependencies in the relation. Drug  Dosage? No Customer  (CustomerName, CustomerPhone)? Yes PrescriptionNumber  (Date, Drug, Dosage, CustomerName, CustomerPhone, Customer ) This is a trivial dependency by the definition of candidate key

Normalization Process: Example 1: Step 3 IST2106 Step 3. If any determinant is not a candidate key, the relation is not well formed. Determinant: PrescriptionNumber, Customer Candidate key: PrescriptionNumber Customer is NOT a candidate key, so the relation NOT well formed Then, we will normalize it (break it into multiple relations)

Normalization Process: Example 1: Step 3 IST2107 Step 3. Examine the determinants of the functional dependencies. If any determinant is not a candidate key, the relation is not well formed. In this case: a.Place the columns of the functional dependency in a new relation of their own. CUSTOMER (Customer , CustomerName, CustomerPhone) b.Make the determinant of the functional dependency the primary key of the new relation. CUSTOMER (Customer , CustomerName, CustomerPhone) c.Leave a copy of the determinant as a foreign key in the original relation. PRESCRIPTION(PrescriptionNumber, Date, Drug, Dosage, Customer ) d.Create a referential integrity constraint between the original relation and the new relation. Customer in PRESCRIPTION must exist in Customer in CUSTOMER

Normalization Process: Example 1: Step 4 IST2108 Step 4. Repeat step 3 as many times as necessary until every determinant of every relation is a candidate key. CUSTOMER (Customer , CustomerName, CustomerPhone) PRESCRIPTION(PrescriptionNumber, Date, Drug, Dosage, Customer ) Customer in PRESCRIPTION must exist in Customer in CUSTOMER Well-formed relational model design

Normalization Process: Exercise 1 IST2109 Step 1. Candidate keys: Step 2. Functional dependencies: Step 3. Determine if the relation is well-formed. If not, split the relation into multiple well-formed relations and specify all the primary keys, foreign keys and referential integrity constraints: Hint: If any determinant is not a candidate key, the relation is not well formed.

Normalization Process: Exercise 2 IST21010 Step 1. Candidate keys: Step 2. Functional dependencies: Step 3. Determine if the relation is well-formed. If not, split the relation into multiple well-formed relations and specify all the primary keys, foreign keys and referential integrity constraints: Hint: If any determinant is not a candidate key, the relation is not well formed.

Normalization Process: Exercise 3 IST21011 Step 1. Candidate keys Step 2. Functional dependencies GRADE(ClassName, Section, Term, Grade, StudentNumber, StudentName, Professor, ProfessorDepartment, Professor ) Step 3. Determine if the relation is well-formed. If not, split the relation into multiple well-formed relations and specify all the primary keys, foreign keys and referential integrity constraints: Hint: If any determinant is not a candidate key, the relation is not well formed.

Summary of Chapter 2 Learn the concept of the relational model: entities, relations, relationships Learn the meaning and importance of keys, foreign keys, and related terminology Learn the meaning of functional dependencies Learn to apply a process for normalizing relations IST21012

True/False Review Questions Given the functional dependency for the attributes of ENTITY1, X → (A, B, C), X is a candidate key for the relation ENTITY1 (A, B, C, X). Normalization is the process of removing all functional dependencies from a relation. In the normalization process, it is not necessary to identify all the functional dependencies in a relation. In the normalization process, if you find a candidate key that is not a primary key, then you have determined that the relation needs to be broken into two or more relations.