ER model(entity relationship model)¶
Symbols to be used¶
Entity ā Rectangle
- What: A real-world thing or object class (table candidate).
- Notation: Rectangle with entity name inside.
- College example: Student, Faculty, Staff, Course, Department.
- Notes: Instances = rows/tuples.
Attribute ā Oval (Ellipse)
- What: Property of an entity.
- Notation: Single oval connected to its entity.
- College example: Student ā Name, DOB, Email.
Composite Attribute ā Oval with sub-ovals
- What: Attribute that breaks into subparts.
- Notation: Parent oval connected to child ovals.
- College example: Address ā Street, City, PIN.
Multivalued Attribute ā Double oval
- What: Attribute that can have multiple values for one entity.
- Notation: Double-lined oval.
- College example: Student ā PhoneNumbers (student may have several).
Derived Attribute ā Dashed oval
- What: Computable attribute, not stored physically.
- Notation: Oval with dashed outline.
- College example: Age derived from DOB.
Relationship ā Diamond
- What: Association between entities.
- Notation: Diamond connecting participating entities; name inside.
- College example: ENROLLED_IN between Student and Course, TEACHES between Faculty and Course.
Total vs Partial Participation ā Double line vs Single line
- What: Double line = total (every entity instance must participate); single = optional/partial.
- College example: If every Course must belong to a Department ā total participation of Course in offered_by relationship (double line).
Key (Primary Key) ā Underlined attribute
- What: Attribute(s) uniquely identifying an entity instance.
- Notation: Underline the attribute name or mark PK.
- College example: StudentID (PK), CourseCode (PK).
