University Schema: ER Example

University Database

This ER diagram shows how university people, courses, and facilities are connected. Read rectangles as entity sets, diamonds as relationships, and follow the connecting lines to see the constraints.

University ER diagram

Entities and keys

• Strong entities: student, instructor, department, course, classroom, and time_slot have underlined key attributes.
• Weak entity: section depends on course. The double rectangle and double diamond sec_course mark this dependency. A section is identified by its course and its section details (sec_id, semester, and year).

Relationships and constraints

Relationship	How to read it
course_dept, inst_dept, stud_dept	Courses, instructors, and students are associated with departments. Each arrow toward department means each participating entity is associated with at most one department.
advisor	Connects students to instructors. The arrow toward instructor means each student has at most one advisor.
teaches	Connects instructors and sections; the diagram allows many-to-many participation.
takes	Connects students and sections. grade describes a student’s result for that section, not a property of the student alone.
prereq	Connects a course to another course. The role names course_id and prereq_id distinguish the course from its prerequisite.
sec_time_slot, sec_class	Connect sections to time slots and classrooms. The arrow toward classroom means each section is associated with at most one classroom.

Reading the notation

• An arrow marks the “at most one” side; it does not mean participation is mandatory.
• A double line means every entity on that side must participate in the relationship.
• A double rectangle marks a weak entity; its double diamond is the identifying relationship.
• An underlined attribute is a key; a dashed underline marks a partial key.

This is a core ER diagram. See Advanced ER Concepts for specialization, ternary relationships, and aggregation.