Introduction to Database Design Database Management Systems, 3rd ed., Ramakrishnan and Gehrke, Chapter 2

Figure 2.5: Roles Name SSN Lot Employees supervisor subordinate ReportsTo 2

Relationship Cardinalities: Mappings . . . . . . 1:1 1:N N:M 3

Key Constraint: 1:N FName SectNum CourseNum Room SSN Office Class Teaches Faculty Each class has only one (at most one) instructor. 4

N:M Relationship SName SectNum CourseNum Room SSN Major Class Takes Student More than 1 student may take a given class; more than 1 class may be taken by a given student. 5

1:1 Relationship Since Name FName SSN Office ID Major Faculty Mentors Student Each faculty member may serve as the mentor for only 1 student; each student may have only 1 mentor. 6

Participation Constraint Indicates whether existence of entity depends on its being related to another entity via a relationship set. Total participation constraint (existence dependency) – Every dependent entity must be related to an entity in the entity set on which it is dependent. Partial participation constraint – Some of the dependent entities are related to entities in the other entity set. 7

Example of Total Participation FName DName MainOffice SSN Office Faculty WorksFor Department Participation constraint: Each faculty member must work for some (i.e., at least one) department. A faculty entity cannot exist without being assigned to a department. Key constraint: Each faculty member may work for at most one department. 8

Figure 2.11: Weak Entity Set Name Cost PName Age SSN Lot Employees Policy Dependents Partial key is shown in blue rather than with a broken underline. 9

Figure 2.14: Entity vs. Attribute DName Name To From DID Budget SSN Lot Employees WorksIn4 Departments Problem with this design: Does not allow an employee to work in a given department over more than one time period. 10

Figure 2.15: Entity vs. Attribute DName Name DID Budget SSN Lot Employees WorksIn4 Departments From Duration To 11

ISA Hierarchy Name GPA ID Students Thesis Group ISA UnderGrads Grads 12

Figure 2.16 Name DBudget Since DName SSN DID Lot Budget Employees Manages2 Departments What are the problems with this design? 13

Revised Figure 2.16 Name SSN Lot Employees DBudget DName ISA Since DID Departments Other entity sets Manages2’ Managers 14

Figure 2.17 Name PName Age SSN Lot Dependents Employees Covers Cost PolicyID Policies 15

Figure 2.17 Name PName Age SSN Lot Dependents Employees Covers Beneficiary Policies Cost PolicyID 16

Subset of Figure 2.13 Departments PID StartedOn Projects PBudget Sponsors DID Budget Since DName 17

Figure 2.13 Departments PID StartedOn Projects PBudget Sponsors DID Since DName Monitors Employees Until SSN Name Lot 18

Figure 2.19 Name Lot SSN Employees StartedOn DName PBudget DID Budget PID Projects Sponsors2 Departments 19

Another Aggregation Example Information about applicants who have interviewed for a position at a company: CAddress ContactPhone CName Address ContactName Date Company Interview JobApplicant Phone SSN Name Fundamentals of Database Systems, Elmasri and Navathe 20

Example (continued) We want to associate a job offer with an interview. Why won’t this work? Company Interview JobApplicant JobOffer Attributes have been omitted for brevity. 21

Example (continued) Possible solution: Company Applied JobApplicant ResultsIn JobOffer Interview 22

Example (continued) More desirable solution conceptually: JobApplicant Company Interview ResultsIn JobOffer 23