Core Concept Mastery • DBMS Module
Imagine filling out a Government Form.
Derived Attribute (Dashed Oval): If the form asks for "Age", you might write 20 today. Next year, that's wrong. That's why they ask for "Date of Birth". The system auto-calculates Age. This calculation is a Derived Attribute.
Multi-valued Attribute (Double Oval): If they ask for "Phone Number", what if you have 2? You need 2 lines. In a database, this needs special treatment (Double Oval), otherwise only the first number gets saved.
Composite Attribute: "Address" isn't just one line. It has H.No, Street, City, Zip... parts. This is a Composite Attribute.
Real life is complex! People have multiple phone numbers, and everyone gets older every year. Our diagram needs special symbols to handle these changing facts.
We don't store "Age" because it changes. We store "Birth Date" and calculate Age (Derived). For phones, we might have Home, Mobile, and Work (Multi-valued).
"A dashed ellipse represents which type of attribute?"
Derived Attribute.