COMP231 Tutorial 1 ER Model and ER to Relational Schema

E-R Diagram Rectangles – entity sets Ellipses – attributes Diamonds – relationship sets Double ellipses – multivalued attributes Dashed ellipses – derived attributes Double lines – total participation Double rectangles – weak entity sets Double diamonds – identifying relationship sets 2

Exercise 1.1 Construct E-R Diagram A university registrar’s office maintains data about the following entities: courses, including number, title, credits, syllabus, and prerequisites; course offerings, including course number, year, semester, section number, instructor(s), timings, and classroom; students, including student-id, name, and program; instructors, including identification number, name, department, and title. Further, the enrollment of students in courses and grades awarded to students in each course they are enrolled must be appropriately modeled. Construct an E-R diagram for the registrar’s office.

Entities course-offering instructor student course

Course “courses including number, title, credits, syllabus, and prerequisites” Attribute? Relationship? courseno credits prerequisite requires course maincourse syllabus title

Course Offering “course offerings, including course number, year, semester, section number, instructor(s), timings, and classroom” semester time courseno course- offering is_offered room course secno year

Weak Entity A weak entity can only be identified uniquely by combining the primary key of another (owner) entity and the partial key of itself. Owner entity set and weak entity set must participate in one-to-many relationship (one owner entity, many weak entities). Weak entity set must have total participation in this identifying relationship set. 4

Student, Instructor “students, including student-id, name, and program” “instructors, including identification number, name, department, and title” sid name iid name student instructor program dept title

Enrollment “Further, the enrollment of students in courses and grades awarded to students in each course they are enrolled must be appropriately modeled.” course-offering enrolls student grade

Anymore?? Instructor teaches course….. course-offering instructor

E-R Diagram for a University

Exercise 1.2 Covert E-R Diagram into Tables

Entities (Not Weak)

Entities (Not Weak) course (courseno, title, syllabus, credits) student (sid, name, program) instructor (iid, name, dept, title)

Weak Entities

Weak Entities course-offering (courseno, secno, year, semester, time, room)

Relationships (Not defining weak entities)

Relationships (Not defining weak entities) enrolls (sid, courseno, secno, semester, year, grade) teaches (courseno, secno, semester, year, iid) requires (maincourse, prerequisite)

Relationships with Weak Entities

Relationships with Weak Entities There is no extra table for the relationship between a weak entity and its strong entity. The relationship is already present in the schema for the weak entity. course-offering (courseno, secno, year, semester, time, room)

Relational Schemas for a University course (courseno, title, syllabus, credits) student (sid, name, program) instructor (iid, name, dept, title) course-offering (courseno, secno, year, semester, time, room) enrolls (sid, courseno, secno, semester, year, grade) teaches (courseno, secno, semester, year, iid) requires (maincourse, prerequisite)

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