1. Employee and Company Relationship 1: Employment An employee works for the company. Example: Employee → Company (association: "works for"). Relationship 2: Shareholding An employee can also own shares in the company. Example: Employee → Company (aggregation or association: "owns shares of"). Here, the same two entities, Employee and Company, are connected in two distinct ways—one as an employer-employee relationship, and another as a shareholder-company relationship.
2. Student and Course Relationship 1: Enrollment A student is enrolled in a course. Example: Student → Course (association: "enrolled in"). Relationship 2: Evaluation A student is evaluated for performance in the course. Example: Student → Course (association: "graded by"). The enrollment relationship is about participating in the course, while the evaluation relationship concerns grading. These relationships are complementary but independent.
3. Author and Book Relationship 1: Authorship An author writes a book. Example: Author → Book (composition: "writes"). Relationship 2: Ownership An author might own copies of the book or rights to it. Example: Author → Book (aggregation: "owns rights to").