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Chapter 9

Relational Database Design by ER- and EER-to-Relational Mapping . Chapter 9. Lecture # 20 August 4 ,2012. Review of ER-to-Relational Mapping Algorithm. We present the concepts of a general mapping algorithm Algorithm has 7 steps: Step 1: Mapping of regular (strong) entity types

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Chapter 9

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  1. Relational Database Design by ER- and EER-to-Relational Mapping Chapter 9 Lecture # 20 August 4 ,2012

  2. Review of ER-to-Relational Mapping Algorithm • We present the concepts of a general mapping algorithm • Algorithm has 7 steps: • Step 1: Mapping of regular (strong) entity types • Step 2: Mapping of weak (dependent) entity types • Steps 3, 4, 5: Mapping of binary relationship types of different cardinality ratios (1:1, 1:N, M:N) • Step 6: Mapping of multi-valued attributes • Step 7: Mapping of n-ary relationship types, n > 2 • Example: We use the COMPANY ER schema diagram (Figure 9.1, next slide) to illustrate the mapping steps • Additional steps (Steps 8, 9) for mapping EER model constructs (specialization/generalization, UNION types) presented later

  3. EER To Relational MappingsMapping of Specialization or Generalization • Step 8: Options for Mapping Specialization or Generalization. • Option 8A: Multiple relations—superclass and subclasses. • Option 8B: Multiple relations—subclass relations only. • Option 8C: Single relation with one type attribute. • Option 8D: Single relation with multiple type attributes.

  4. EER To Relational MappingsMapping of Specialization or Generalization • Step 8: Options for Mapping Specialization or Generalization. • Option 8A: Suitable for Total, Partial Disjoint or Overlapping • Option 8B: Recommended only for disjoint • Option 8C: Works only for disjoint • Option 8D:Works for specializations whose subclasses are overlapping.

  5. EER To Relational MappingsMapping of Specialization or Generalization • Step 8: Options for Mapping Specialization or Generalization. • Options 8A and 8B can be called the multiple-relation options. • 8C and 8D can be called the single-relation options

  6. EER Model Example

  7. EER Model Example

  8. EER Model Example

  9. Example

  10. Another Example

  11. EER To Relational MappingsMapping of Union Types • Step 9: Mapping of Union Types (Categories). For mapping a category whose defining super classes have different keys, it is customary to specify a new key attribute, called a surrogate key, when creating a relation to correspond to the category.

  12. Union Type-Example

  13. In-Class Exercises • Apply the ER-to-Relational Mapping Algorithm to the SHIP_TRACKING ER Schema in Figure 9.8 (next slide)

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