Conversion from ER diagram to relational model
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Conversion from ER diagram to relational model







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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.
Conversion from ER diagram to relational model

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Slide 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

Slide 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

Slide 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

Slide 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

Slide 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

Slide 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

Slide 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

Slide 8

Multi valued attributes

  • Multi valued attributes

    • Own relation

    • Foreign key to the “owning” relation.

Conversion from ER diagram to relational model

Slide 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

Slide 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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