ER图应用举例.docVIP

A company database needs to store information about employees (identi?ed by ssn,with salary and phone as attributes), departments (identi?ed by dno, with dname and budget as attributes), and children of employees (with name and age as attributes). Employees work in departments; each department is managed by an employee; a child must be identi?ed uniquely by name when the parent (who is an employee; assume that only one parent works for the company) is known. We are not interested in information about a child once the parent leaves the company. Draw an ER diagram that captures this information. 2 Consider the following information about a university database: Professors have an SSN, a name, an age, a rank, and a research specialty. Projects have a project number, a sponsor name (e.g., NSF), a starting date, an ending date, and a budget. Graduate students have an SSN, a name, an age, and a degree program (e.g., M.S.or Ph.D.). Each project is managed by one professor (known as the project’s principal inves-tigator). Each project is worked on by one or more professors (known as the project’s co-investigators). Professors can manage and/or work on multiple projects. Each project is worked on by one or more graduate students (known as the project’s research assistants). When graduate students work on a project, a professor must supervise their work on the project. Graduate students can work on multiple projects, in which case they will have a (potentially di?erent) supervisor for each one. Departments have a department number, a department name, and a main o?ce. Departments have a professor (known as the chairman) who runs the department. Professors work in one or more departments, and for each department that they work in, a time percentage is associated with their job. Graduate students have one major department in which they are working on their degree. Each graduate student has another, more senior graduate student (known as a student advisor) who advises him or her o