E-R Diagrams
The Basic Structure of an E-R diagram will have the following components.
Rectangles: These are classified into two parts. The first half coloured in blue contains the name of the entity set. The second half in white contains the names of all the attributes. The attributes that are part of the key are underlined.
Diamonds: These represent relationship sets.
Undivided Rectangles: These represent the attributes present in a relationship set.
Lines: The lines help us to link entity sets to relationship sets.
Dashed Lines: These help link attributes of a relationship set to another relationship set.
Double Lines: These indicate the total participation of an entity in a relationship set.
Double Diamond: These represent identifying relationship sets that are linked to weak entity sets.
E-R diagrams show a way to point out complex constraints on the number of times every entity takes part in the relationships in a relationship set.