Date 09112019 Chapter 2 37 Class Activity 25 4 minutes b Determine the

# Date 09112019 chapter 2 37 class activity 25 4

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Date 09/11/2019 Chapter 2 37 Class Activity 2.5 (4 minutes) b. Determine the cardinalities in the Clothing Shop ERD.
Date 09/11/2019 Chapter 2 38 Solution- Cardinalities
Date 09/11/2019 Chapter 2 39 1.4. Relationship: Multiple Relationships Between Entities Two entities can have more than one type of relationship between them (multiple relationships) a) Figure 2-21: Employees and departments b) Figure 2-21: Professors and courses ( fixed lower limit constraint ) Entities can be related to one another in more than one way Here, 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 09/11/2019 Chapter 2 40 1.5. Associative Entities
Date 09/11/2019 Chapter 2 41 1.5. Associative Entities An associative Entity is an entity – has attributes An associative Entity is a relationship – links entities together When should a relationship with attributes instead be an associative entity ? All relationships for the associative entity should be many The associative entity could have meaning independent of the other entities The associative entity preferably has a unique identifier , and should also have other attributes The associative entity may participate in other relationships other than the entities of the associated relationship Many-to-Many and Ternary relationships should be converted to associative entities
Date 09/11/2019 Chapter 2 42
Date 09/11/2019 Chapter 2 43 1.5. PK of associative entity Employee Employee ID Employee Name Birth Date 1234587 Jack 1/1/1960 3459087 Michael 5/2/1985 Certificate Employee ID Course ID Date Completed 1234587 C68 1/1/2017 3459087 A57 1/2/2016 3459087 C68 5/10/2016 Course Course ID Course Title Topic A57 Knowledge Management …. C68 Project Management …. Rule: in each one-to-many relationships, PK of the entity on one side is FK of the entity on the many side FK FK PK PK
Date 09/11/2019 Chapter 2 44 1.5. Cardinality constraints in a ternary relationship (Figure 2-18)
Date 09/11/2019 Chapter 2 45