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Databases 103

Databases 103. Entities and Attributes. Two Entities. ENTITY( Primary Key , Attribute, Attribute2, Attribute3, Foreign Key ). CUSTOMER( Cid , Name, Address, DOB, Postcode, Allowed, Vid ) VIDEO( Vid , Name, Cast, Rating, Condition). Attribute = Name. Attribute = Postcode. Attribute = DoB.

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Databases 103

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  1. Databases 103

  2. Entities and Attributes

  3. Two Entities ENTITY(Primary Key, Attribute, Attribute2, Attribute3, Foreign Key) CUSTOMER(Cid, Name, Address, DOB, Postcode, Allowed, Vid) VIDEO(Vid, Name, Cast, Rating, Condition)

  4. Attribute = Name Attribute = Postcode Attribute = DoB Entity = Customer Attribute = Address Attribute = CUSTID Entities and Attributes Attribute = Age Attribute = Title Entity = DVD Attribute = Condition Attribute = DVDID

  5. Databases Two and Three Student Course Repeating Group

  6. The three normal forms

  7. First idea ….. • STUDENT(student number, student name, DoB, Sex, course1, course2, course3) • COURSE(course number, course name, teacher number, teacher name) This is called a repeating attribute It is not allowed in First Normal form This is called a repeating attribute It is not allowed in First Normal form

  8. First idea ….. • STUDENT(student number, student name, DoB, Sex, course number) • COURSE(course number, course name, teacher number, teacher name) This is called a repeating attribute It is not allowed in First Normal form This is called a repeating attribute It is not allowed in First Normal form

  9. First Normal Form • STUDENT(student number, student name, DoB, Sex, course number) • COURSE(course number, course name, teacher number, teacher name)

  10. First Normal Form No repeating attributes or repeating groups of attributes

  11. Second Normal Form Key • No partial dependencies What does that mean? Student name and sex are dependent only on part of the key They are unrelated to Course no.

  12. Second Normal Form • STUDENT(student number, student name, DoB, Sex) • STUDENT_TAKES(student number, course number) • COURSE(course number, course name, teacher number, teacher name)

  13. Many to Many in Second Normal Form Student Course Link Student Course

  14. Third Normal Form • No ‘non key’ dependencies In this case, teacher name is dependent on teacher no, not course number So we break the table into two

  15. Third Normal Form • STUDENT(student number, student name, DoB, Sex) • STUDENT_TAKES(student number, course number) • COURSE(course number, course name, teacher number) • TEACHER(teacher number, teacher name)

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