Presentation on theme: "Complex entities and relationships Case examples are from the book: Lars Fank Databaser Teori og Praksis ISBN 87-571-2397-7."— Presentation transcript:
Complex entities and relationships Case examples are from the book: Lars Fank Databaser Teori og Praksis ISBN 87-571-2397-7
Short repetition: Many-to-many, One-to-many, trees, and network relationships:
Repetition: One-to-many relationships
Repetition: Many-to-many relations.
Different illustrations of tree structure relationships:
Different illustrations of network structure relationships:
Relationship degree Type of relationshipRelationship degree One-to-many relationshipBinary Many-to-many relationshipBinary One-to-one relationshipBinary Tree structure relationshipUnary Network relationshipUnary Order relationshipUnary Relationship of degree NN-ary
Different illustrations of simple relationships of order 3.
Different illustrations of simple relationships of degree 3.
ER and Bachman illustrations of the relationship of order three.
An ER relationship need not be implemented as a table or a forign key How would you convert the Bachman diagram to an ER-diagram with normalized tables?
Entities and relationships must not be connected directly in ER-diagrams. Therefore, ER-diagrams need a pseudoentity if two relationships need to be connected
ER relationships may be viewed as Bachman entities depending on the application area.
ER versus Bachman diagrams: In this course you should not use ER-diagrans because they are ambiguous