ER & EER to Relational Mapping
ER & EER to Relational Mapping
Chapter 9
1
Figure 3.2 ER schema diagram for the company database.
Fname
Minit
Lname
S__s_n Bdate
Name
Address
Sex
Salary
EMPLOYEE
supervisor
1
SUPERVISION
supervisee N
N
1
WORKS_FOR
Number
Name
Locations
StartDate
NumberOfEmployees
1
1
MANAGES
DEPARTMENT
1
CONTROLS
Hours N
WORKS_ON 1
DEPENDENTS_OF
N
PROJECT
Name N__u_m_b_e_r
Location
N
DEPENDENT
Name
Sex
BirthDate
Relationship
? Addison Wesley Longman, Inc. 2000, Elmasri/Navathe, Fundamentals of Database Systems, Third Edition
Step 1: For each regular entity type E
? Create a relation R that includes all the simple attributes of E.
? Include all the simple component attributes of composite attributes.
? Choose one of the key attributes of E as primary key for R.
? If the chosen key of E is composite, the set of simple attributes that form it will together form the primary key of R.
Chapter 9
2
Figure 7.5 Schema diagram for the COMPANY relational database schema; the primary keys are underlined.
EMPLOYEE FNAME MINIT
LNAME SSN BDATE ADDRESS
SEX SALARY SUPERSSN DNO
DEPARTMENT DNAME DNUMBER
MGRSSN
MGRSTARTDATE
DEPT_LOCATIONS DNUMBER DLOCATION
PROJECT PNAME PNUMBER
PLOCATION
DNUM
WORKS_ON ESSN PNO HOURS
DEPENDENT ESSN DEPENDENT_NAME
SEX BDATE RELATIONSHIP
? Addison Wesley Longman, Inc. 2000, Elmasri/Navathe, Fundamentals of Database Systems, Third Edition
Step 2: For each weak entity type W with owner entity type E
? Create a relation R, and include all simple attributes and simple components of composite attributes of W as attributes of R.
? In addition, include as foreign key attributes of R the primary key attribute(s) of the relation(s) that correspond to the owner entity type(s).
Chapter 9
3
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