E r to relational mapping
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E/R to relational mapping. E/R to relational mapping algorithm – overview Mapping algorithm step 1-7 Steen Jensen, autumn 2013. E/R to relational mapping algorithm - overview. The next slides shows an algorithm for converting an E/R diagram to a relational model

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E r to relational mapping

E/R to relational mapping

  • E/R to relational mapping algorithm – overview

  • Mapping algorithm step 1-7

  • Steen Jensen, autumn 2013


E r to relational mapping algorithm overview

E/R to relational mapping algorithm - overview

  • The next slides shows an algorithm for converting an E/R diagram to a relational model

  • The algorithm contains 7 steps:

    • Mapping of regular entity types

    • Mapping of weak entity types

    • Mapping of binary 1:1 relationship types

    • Mapping of binary 1:N relationship types

    • Mapping of binary M:N relationship types

    • Mapping of multivalued attributes

    • Mapping of N-ary relationship types


E r to relational mapping algorithm base example

E/R to relational mapping algorithm – base example

The steps will be based upon figure 7.1 from Elmasri chapter 7


E r to relational mapping algorithm step 1 mapping of regular entity types

E/R to relational mapping algorithm – step 1- mapping of regular entity types

  • For each regular (strong) entity type create a relation, that includes all simple attributes

  • Choose one of the attributes as a primary key

  • See a) in the below figure


E r to relational mapping algorithm step 2 mapping of weak entity types

E/R to relational mapping algorithm – step 2- mapping of weak entity types

  • For each weak entity type create a relation, that includes all simple attributes

  • Include as foreign key the primary key(s) of the relation(s) corresponding to the ownerentity type(s)

  • The primary key is the combination of the foreign key and the partial key of the weak entity

  • See b) in the below figure


E r to relational mapping algorithm step 3 mapping of binary 1 1 relationship types

E/R to relational mapping algorithm – step 3- mapping of binary 1:1 relationship types

  • Include a foreign key in one of the entities taking part of the relationship (pick either end)

  • Also include any attributes from the relationship

  • See the below figure – here the entity type Department is chosen (relationship Manages)


E r to relational mapping algorithm step 4 mapping of binary 1 n relationship types

E/R to relational mapping algorithm – step 4- mapping of binary 1:N relationship types

  • Include a foreign key in the N-side of the relationship

  • Also include any attributes from the relationship

  • See the below figure – the relationships Works_for, Controls and Supervision has been implemented)


E r to relational mapping algorithm step 5 mapping of binary m n relationship types

E/R to relational mapping algorithm – step 5- mapping of binary M:N relationship types

  • Each M:N relationship is converted into a relation with a combined primary key (the primary key from both participating entities)

  • Also include any attributes from the relationship

  • See c) in the below figure – the relationship Works_onhas been implemented


E r to relational mapping algorithm step 6 mapping of multivalued attributes

E/R to relational mapping algorithm – step 6- mapping of multivalued attributes

  • Each multivalued attribute is converted into a relation with a combined primary key: the attribute itself + foreign key

  • For each value a tuple will exist in the new relation

  • See d) in the below figure – the multivalued attribute Locations has been implemented


E r to relational mapping algorithm step 7 mapping of n ary relationship types

E/R to relational mapping algorithm – step 7- mapping of N-ary relationship types

Figure3.17 from chapt. 3 in Elmasri

Figure7.4 from chapt. 7 in Elmasri

  • Each N-ary relationship is converted into a relation with a combined primary key (the primary keys from all participating entities)

  • Also include any attributes from the relationship


Assignment map e r diagram for amazon to a relational model

Assignment: Map E/R diagram for Amazon to a relational model

Continue with your solution for Amazon – the E/R diagram

Follow the steps described in the slides and convert the E/R diagram into a relational model

Start today and continue at home, so you can present a solution next time in class – make a Word document with the relational models and upload it to the folder called Relational models for Amazonin studie.rhs.dk


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