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Some other symbols for ER-Diagrams
Weak entity:◦ An entity that depends on another entity
Key attribute:o A key attribute is the unique, distinguishing characteristic of the entity
Some other symbols for ER-Diagrams
Multivalued attribute:A multivalued attribute can have more than one value. For example, an employee entity can have multiple skill values.
Derived attribute:A derived attribute is based on another attribute. For example, an employee's monthly salary is based on the employee's annual salary.
Relationships in ER-Diagrams There are three types of relationships:
1. Binary relationship
2. Recursive relationship
3. Ternary relationship
Binary relationships◦ Relationship between two entities◦ Cardinality
◦ It has further 3 types:1. One to one relationship2. One to many relationship3. Many to many relationship
Binary relationships One to many relationship:
It reflects business rule in which one entity is related to many number of other entity.
Binary relationships Many to many relationship:
Many entities have relationship to many other entities
Participation Constraints in ER-Diagrams
Total Participation: Each entity in the entity is involved in the relationship. Total participation is represented by double lines.
Partial participation: Not all entities are involved in the relation ship. Partial participation is represented by single line.