ER Diagrams [18 points]
[4 points] True or False:
1. ER diagrams are used to model the physical schema of a database.
? ??False, they are used to model the logical schema. Physical schema refers to things like file and index layout.
2. An entity set E can be associated with a relationship set R more than once.
? ??True, for example a relationship Reports_To which has the entity Employees participating twice, since Managers are also Employees.
3. At most 2 distinct entity sets can be associated with any relationship set R.
? ??False, for example, a ternary relationship “Covers” with participating entities Employees, Dependents, and Policies.
4. A weak entity set must have total participation in its identifying relationship set.
? ??True, by definition.
