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The Relational Database Design

The Relational Database Design. ER- and EER-to-Relational Mapping. ER to Relational Mapping. Mapping of regular entity types Multivalued attributes Mapping of relationship Binary relationship N-ary relationship Mapping of weak entity types Mapping of specialization and generalization.

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The Relational Database Design

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  1. The Relational Database Design ER- and EER-to-Relational Mapping

  2. ER to Relational Mapping • Mapping of regular entity types • Multivalued attributes • Mapping of relationship • Binary relationship • N-ary relationship • Mapping of weak entity types • Mapping of specialization and generalization

  3. FIGURE 7.1: The ER conceptual schema diagram for the COMPANY database.

  4. Regular Entity Types • Mapping • Create a new relation. • Include all the (simple) attributes of the entity. • Choose one of the key attribute as primary key.

  5. Multivalued Attributes • Mapping • Create a new relation R for each multivalued A. • Include an attribute corresponding to A and the primary key attribute K (as a foreign key in R) • The primary key of R is K and A.

  6. Binary Relationships • Binary M:N relationships • Create a new relation S. • Include as foreign keys the primary keys of the participating entities. The primary key of S is the combination of these. • Include all the (simple) attributes of the relationship type.

  7. Binary Relationships • Binary 1:1 relationships • Choose the entity with total participation. • Include the primary key of the other relation as a foreign key. • Include all the (simple) attributes of the relationship.

  8. Binary Relationships • Binary 1:N relationships • Choose the entity at the N side. • Include the primary key of the other relation as a foreign key. • Include all the (simple) attributes of the relationship.

  9. N-ary Relationships • Mapping • Create a new relation S. • Include as foreign keys the primary keys of the participating entities. The primary key of S is the combination of these. • Include all the (simple) attributes of the relationship type.

  10. Weak Entity Types • Mapping • Create a relation. • Include all the (simple) attributes of the weak entity. • Include as a foreign key the primary key of the owner entity. • The primary key is the combination of the primary key of the owner and the partial key of the weak entity.

  11. FIGURE 7.2: Result of mapping the COMPANY ER schema into a relational schema.

  12. FIGURE 7.3: Mapping the n-ary relationship type SUPPLY from Figure 4.11a.

  13. Specialization and Generalization • Mapping • Create a relation for the superclass (similar to mapping a regular entity) • Create a relation for each subclass, include primary key of the superclass (as its primary key) and local attributes.

  14. FIGURE 7.4: Options for mapping specialization or generalization.

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