Conversion from ER diagram to relational model ER

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 1

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 2

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

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 4

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 5

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 6

Multi valued attributes • Multi valued attributes – Own relation – Foreign key to the “owning” relation. Conversion from ER diagram to relational model 7