Date 09/11/2019Chapter 237Class Activity 2.5 (4 minutes)b. Determine the cardinalities in the Clothing Shop ERD.
Date 09/11/2019Chapter 238Solution- Cardinalities
Date 09/11/2019Chapter 2391.4. Relationship: Multiple Relationships Between EntitiesTwo entities can have more than one type of relationship between them (multiple relationships)a) Figure 2-21: Employees and departmentsb) Figure 2-21: Professors and courses (fixed lower limit constraint)Entities can be related to one another in more than one wayHere, min cardinality constraint is 2. BR: At least two professors must be qualified to teach each course. BR: Each professor must be qualified to teach at least one course.
Date 09/11/2019Chapter 2401.5. Associative Entities
Date 09/11/2019Chapter 2411.5. Associative EntitiesAn associative Entity is an entity– has attributesAn associative Entity is a relationship– links entities togetherWhen should a relationship with attributes instead be an associative entity? All relationships for the associative entity should be manyThe associative entity could have meaning independent of the other entitiesThe associative entity preferably has a unique identifier, and should also have other attributesThe associative entity may participate in other relationships other than the entities of the associated relationshipMany-to-Many and Ternary relationships should be converted to associative entities
Date 09/11/2019Chapter 242
Date 09/11/2019Chapter 2431.5. PK of associative entityEmployeeEmployee IDEmployee NameBirth Date1234587Jack1/1/19603459087Michael5/2/1985CertificateEmployee IDCourse IDDate Completed1234587C681/1/20173459087A571/2/20163459087C685/10/2016CourseCourse IDCourse TitleTopicA57Knowledge Management….C68Project Management….Rule: in each one-to-many relationships, PK of the entity on one side is FK of the entity on the many side FKFKPKPK
Date 09/11/2019Chapter 2441.5. Cardinality constraints in a ternary relationship (Figure 2-18)