Step 1: Mapping of Regular Entity Types.
For each regular (strong) entity type E in the ER schema, create a relation R that includes all the simple attributes of E.
Choose one of the key attributes of E as the 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.
Example: We create the relations EMPLOYEE,DEPARTMENT, and PROJECT in the relational schema corresponding to the regular entities in the ER diagram.
SSN, DNUMBER, and PNUMBER are the primary keys for the relations EMPLOYEE, DEPARTMENT, and PROJECT as shown.
Step 2: Mapping of Weak Entity Types
For each weak entity type W in the ER schema with owner entity type E, create a relation R & include all simple attributes (orsimple components of composite attributes) of W as attributes of
R.
Also, include as foreign key attributes of R the primary key attribute(s) of the relation(s) that correspond to the owner entity type(s).
The primary key of R is the combination of the primary key(s) of the owner(s) and the partial key of the weak entity type W, if any.
Example: Create the relation DEPENDENT in this step to correspond to the weak entity type DEPENDENT.
Include the primary key SSN of the EMPLOYEE relation as a foreign key attribute of DEPENDENT (renamed to ESSN).
The primary key of the DEPENDENT relation is the combination {ESSN, DEPENDENT_NAME} because DEPENDENT_NAME is the partial key of DEPENDENT.
Step 6: Mapping of Multivalued attributes.
For each multivalued attribute A, create a new relation R.
This relation R will include an attribute corresponding to A, plus the primary key attribute K-as a foreign key in R-of the relation that represents the entity type of relationship type that has A as an
attribute.
The primary key of R is the combination of A and K. If the multivalued attribute is composite, we include its simple components.
Example: The relation DEPT_LOCATIONS is created.
The attribute DLOCATION represents the multivalued attribute LOCATIONS of DEPARTMENT, while DNUMBER-as foreign keyrepresents the primary key of the DEPARTMENT relation.
The primary key of R is the combination of {DNUMBER, DLOCATION}.
For each regular (strong) entity type E in the ER schema, create a relation R that includes all the simple attributes of E.
Choose one of the key attributes of E as the 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.
Example: We create the relations EMPLOYEE,DEPARTMENT, and PROJECT in the relational schema corresponding to the regular entities in the ER diagram.
SSN, DNUMBER, and PNUMBER are the primary keys for the relations EMPLOYEE, DEPARTMENT, and PROJECT as shown.
Step 2: Mapping of Weak Entity Types
For each weak entity type W in the ER schema with owner entity type E, create a relation R & include all simple attributes (orsimple components of composite attributes) of W as attributes of
R.
Also, include as foreign key attributes of R the primary key attribute(s) of the relation(s) that correspond to the owner entity type(s).
The primary key of R is the combination of the primary key(s) of the owner(s) and the partial key of the weak entity type W, if any.
Example: Create the relation DEPENDENT in this step to correspond to the weak entity type DEPENDENT.
Include the primary key SSN of the EMPLOYEE relation as a foreign key attribute of DEPENDENT (renamed to ESSN).
The primary key of the DEPENDENT relation is the combination {ESSN, DEPENDENT_NAME} because DEPENDENT_NAME is the partial key of DEPENDENT.
Step 6: Mapping of Multivalued attributes.
For each multivalued attribute A, create a new relation R.
This relation R will include an attribute corresponding to A, plus the primary key attribute K-as a foreign key in R-of the relation that represents the entity type of relationship type that has A as an
attribute.
The primary key of R is the combination of A and K. If the multivalued attribute is composite, we include its simple components.
Example: The relation DEPT_LOCATIONS is created.
The attribute DLOCATION represents the multivalued attribute LOCATIONS of DEPARTMENT, while DNUMBER-as foreign keyrepresents the primary key of the DEPARTMENT relation.
The primary key of R is the combination of {DNUMBER, DLOCATION}.
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