5. Question
Which of the following plays an important role in representing information about the real world in a database? Explain briefly
1)DDL )DML 3)Buffer manager 4)the data model

6. E-R Model
Attribute
Attribute
Employees
ssn
name
lot
Attribute
Entity

7. E-R Model dname did dbudget Department Attribute Attribute Attribute
Entity

8. Figure. The Report_To Relationship Set
name
ssn
lot
Employees
super-visor
subor-dinate
Reports_To
Figure. The Report_To Relationship Set
since
name
dname
ssn
lot
did
budget
Employees
Works_In
Departments
Figure. The Works_in Relationship set

9. E-R Model Figure. Key Constraint on Manages since lot name ssn dname
did
budget
Manages
Employees
Departments
Figure. Key Constraint on Manages

10. Mapping cardinality of a relationship
1-to-1
1-to Many
Many-to-1
Many-to-Many

11. 1-to-many

12. Many - 1

13. Many - many

14. Alternative Cardinality Specification

15. Department major offers faculty teaches Professor advisor enrollment
Courses
teaches
Professor
advisor
enrollment
Students

16. Department major offers faculty teaches Professor advisor enrollment
Courses
teaches
Professor
advisor
enrollment
Students

17. Participation Constraints
since
since
name
name
dname
dname
ssn
lot
did
did
budget
budget
Employees
Manages
Departments
Works_In
since

18. Weak Entities
name
cost
ssn
lot
pname
age
Employees
Policy
Dependents

19. ISA (`is a’) Hierarchies
name
ssn
lot
Employees
hourly_wages
hours_worked
ISA
contractid
Hourly_Emps
Contract_Emps

20. Aggregation name ssn lot Employees Monitors until started_on since
dname
pid
pbudget
did
budget
Projects
Sponsors
Departments

21. Entity vs. Attribute Figure. The Works_In4 Relationship Set
from to
name
Employees
ssn
lot
dname
did
budget
Works_In4
Departments
Figure. The Works_In4 Relationship Set
name
dname
budget
did
ssn
lot
Employees
Works_In4
Departments
Duration
from to
Figure. The Works_In4 Relationship Set

22. Entity vs. Relationship
since
dbudget
name
dname
ssn
lot
did
budget
Employees
Manages2
Departments
Figure. The Manages2 Relationship Set
name
ssn
lot
since
dname
Employees
did
budget
Manages2
Departments
ISA
This fixes the
problem!
Managers
dbudget
Figure. The Manages2 Relationship Set

23. Binary vs. Ternary Relationships
name
Employees
ssn
lot
pname
age
Covers
Dependents
Bad design
Policies
policyid
cost
<- Figure. Policies as an entity Set
name
Employees
ssn
lot
pname
age
Dependents
Purchaser
Beneficiary
Better design
Figure. PolicyRevisited
policyid
cost
Policies

24. Exercises
1)Explain the following terms briefly:
attribute, domain, entity, relation-ship, entity set, relationship set, one-to-many relationship, many-to-many relationship,
participation constraint, overlap constraint, covering constraint, weak entity set, aggregation, and role indicator

25. 2) A university database contains information about professors (identified
employee id No., or EIN) and courses (identified by courseid). Professors teach courses;
each of the following situations ,concerns the Teaches relationship set.
For each situation, draw an ER diagram that describes it (assuming no further constraints hold)
i. Professors can teach the same course in several semesters, and each offering must be recorded.
ii. Professors can teach the same course in several semesters, and only the most recent such offering needs to be recorded
. (Assume this condition applies in all
subsequent questions.)
iii. Every professor must teach some course

26. iv. every professor teaches exactly one course (no more, no less).
v. Every professor teaches exactly one course (no more, no less), and every course must be taught by some professor

27. vi. Now suppose that certain courses can be taught by a team of professors jointly,
but it is possible that no one professor in a team can teach the course.
Model this situation, introducing additional entity sets and relationship sets if necessary