BINA Assistant Programmer Exam Taker: IBA (2019)প্রশ্ন ও সমাধান

An Entity-Relationship (E-R) diagram is a graphical way to model a database's structure before implementation, showing entities (real-world objects), their attributes (properties), and the relationships between entities.

Core components:

• Entity: a distinct object to store data about (e.g. Student, Course) — drawn as a rectangle.
• Attribute: a property of an entity (e.g. Student has StudentID, Name) — drawn as an oval, underlined if it's the primary key.
• Relationship: an association between two or more entities (e.g. Student enrolls in Course) — drawn as a diamond, with cardinality (1:1, 1:N, M:N) marked on the connecting lines.

Example — Student/Course enrollment system:

erDiagram
  STUDENT ||--o{ ENROLLMENT : has
  COURSE  ||--o{ ENROLLMENT : has
  STUDENT {
    int StudentID PK
    string Name
    string Department
  }
  COURSE {
    string CourseID PK
    string CourseName
    int Credits
  }
  ENROLLMENT {
    int StudentID FK
    string CourseID FK
    string Grade
  }

This shows a many-to-many relationship (a student can enroll in many courses, and a course can have many students), resolved by an associative entity ENROLLMENT that becomes its own table holding both foreign keys.

Why it matters: the E-R diagram is converted directly into relational tables during database design — each entity becomes a table, each attribute a column, and each relationship becomes either a foreign key (1:N) or a junction table (M:N).

Exam takeaway: Entities → tables, Attributes → columns, Relationships → foreign keys or junction tables; cardinality notation (1:1, 1:N, M:N) is what an examiner checks most closely on an E-R diagram.