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Conversion from ER diagram to relational model

Conversion from ER diagram to relational model. ER is a visual model The relational model is a matemathical model. Database development as part of systems development. Analysis phase Draw an ER-diagram Design phase Convert ER-diagram to relational model.

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Conversion from ER diagram to relational model

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  1. Conversion from ER diagram to relational model ER is a visual model The relational model is a matemathical model Conversion from ER diagram to relational model

  2. Database development as part of systems development • Analysis phase • Draw an ER-diagram • Design phase • Convert ER-diagram to relational model. • Check if the relations are sufficiently normalized. • Realization phase • Create tables in a DBMS. Conversion from ER diagram to relational model

  3. Procedure for conversion from ER to relational model • Strong entity types • have their own relation with all the single-valued attributes. • composite attributes: Simple attributes (“leaves”) in the relations. • primary key transferred from ER to the relation. Conversion from ER diagram to relational model

  4. Converting weak entities • Weak entity types • have their own relation with all single-valued attributes • partial key transferred from ER to the relation • foreign key to referring to the “strong” entity (identifying relationship). • primary key = partial key + foreign key to “strong” entity. Conversion from ER diagram to relational model

  5. Binary relationships 1:1 • Binary 1:1 relationships (rare) • data from the relationship (if any) integrated into one of the related entities [your choice]. • one of the related relations gets a foreign key to the other [your choice: easy to find a “way” from on to the other, but not vice versa] • 1:1 relations are rare in ER-diagrams {they are usually modeled as a single entity } Conversion from ER diagram to relational model

  6. Binary relationships 1:N • Binary relationships with cardinality 1:N • data from the relationship (if any) integrated into the relation with the “N” • The “N” relation has a foreign key to the “1” relation. Conversion from ER diagram to relational model

  7. Binary relationships N:M • Binary relationships with cardinality N:M • Own relation with 2 foreign keys (1 for each of the relation entities) • Date (like timestamps, etc.) on the relationships goes into the relation. Conversion from ER diagram to relational model

  8. Multi valued attributes • Multi valued attributes • Own relation • Foreign key to the “owning” relation. Conversion from ER diagram to relational model

  9. N-ary relationships • Relationships with N (more than 2) entities • Own relation with N foreign keys (1 for each related entity) Conversion from ER diagram to relational model

  10. Inheritance, page 295 • ER-modeling allows inheritance between entity types. • Problem • No inheritance in the relational model. • Solution • Try to avoid inheritance in ER. Conversion from ER diagram to relational model

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