ER diagrams
45 min · Intermediate
An ER diagram (entity-relationship diagram) is a picture of the things a system stores and how they are connected, drawn before any table is created. Interviewers often ask you to sketch one for a small system and then turn it into tables; Section 12's Database Design module covers the SQL side in depth.
Topics in this lesson
- Entities and attributes (simple, composite, multivalued, derived)
- Relationships and cardinality (1:1, 1:N, M:N)
- Weak entities and participation
- Converting an ER diagram to tables
- Worked example: a college placement system
Interview questions this lesson answers
- What is an ER diagram?
- What is the difference between an entity and an entity set?
- What symbols are used in a Chen ER diagram?
- What are the types of attributes?
- What is a composite attribute, and how do you store it?
- What is a multivalued attribute, and how do you store it?
- What is a derived attribute? Should it be stored?
- What is a relationship and a relationship set?
- What is the degree of a relationship?
- What is cardinality in ER diagrams?
Sign in free to continue this lesson
Create a free account to read every lesson, practise with the exercises and keep track of your progress.