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Introduction to Database Design
Database Management Systems, 3rd ed., Ramakrishnan and Gehrke, Chapter 2
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Figure 2.5: Roles Name SSN Lot Employees supervisor subordinate
ReportsTo 2
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Relationship Cardinalities: Mappings
. . . . . . 1:1 1:N N:M 3
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Key Constraint: 1:N FName SectNum CourseNum Room SSN Office Class
Teaches Faculty Each class has only one (at most one) instructor. 4
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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
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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
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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
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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
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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
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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
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Figure 2.15: Entity vs. Attribute
DName Name DID Budget SSN Lot Employees WorksIn4 Departments From Duration To 11
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ISA Hierarchy Name GPA ID Students Thesis Group ISA UnderGrads Grads
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Figure 2.16 Name DBudget Since DName SSN DID Lot Budget Employees
Manages2 Departments What are the problems with this design? 13
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Revised Figure 2.16 Name SSN Lot Employees DBudget DName ISA Since DID
Departments Other entity sets Manages2’ Managers 14
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Figure 2.17 Name PName Age SSN Lot Dependents Employees Covers Cost
PolicyID Policies 15
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Figure 2.17 Name PName Age SSN Lot Dependents Employees Covers
Beneficiary Policies Cost PolicyID 16
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Subset of Figure 2.13 Departments PID StartedOn Projects PBudget
Sponsors DID Budget Since DName 17
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Figure 2.13 Departments PID StartedOn Projects PBudget Sponsors DID
Since DName Monitors Employees Until SSN Name Lot 18
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Figure 2.19 Name Lot SSN Employees StartedOn DName PBudget DID Budget
PID Projects Sponsors2 Departments 19
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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
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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
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Example (continued) Possible solution: Company Applied JobApplicant
ResultsIn JobOffer Interview 22
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Example (continued) More desirable solution conceptually: JobApplicant
Company Interview ResultsIn JobOffer 23
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