ch07-Relational Database Design by ER- and EERR-to-Relational Mapping

Ch07-Relational Database Design by ER- and EERR-to-Relational Mapping

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Slide 7- 1 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe
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Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Chapter 7 Relational Database Design by ER- and EERR-to-Relational Mapping
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Slide 7- 3 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Chapter Outline ER-to-Relational Mapping Algorithm Step 1: Mapping of Regular Entity Types Step 2: Mapping of Weak Entity Types Step 3: Mapping of Binary 1:1 Relation Types Step 4: Mapping of Binary 1:N Relationship Types. Step 5: Mapping of Binary M:N Relationship Types. Step 6: Mapping of Multivalued attributes. Step 7: Mapping of N-ary Relationship Types. Mapping EER Model Constructs to Relations Step 8: Options for Mapping Specialization or Generalization. Step 9: Mapping of Union Types (Categories).
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Slide 7- 4 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe ER-to-Relational Mapping Algorithm 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.
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Slide 7- 5 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe FIGURE 7.1 The ER conceptual schema diagram for the COMPANY database.
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Slide 7- 6 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe FIGURE 7.2 Result of mapping the COMPANY ER schema into a relational schema.
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Slide 7- 7 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe ER-to-Relational Mapping Algorithm (contd.) 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 (or simple 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.
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Slide 7- 8 Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe ER-to-Relational Mapping Algorithm (contd.) Step 3: Mapping of Binary 1:1 Relation Types For each binary 1:1 relationship type R in the ER schema, identify the
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Ch07-Relational Database Design by ER- and EERR-to-Relational Mapping

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