For each of the following pairs of rules, identify two entity types and one relationship. State the cardinality for relationship in each case. If you don’t think enough information is available to define either of these, then state an assumption that makes it clear. Draw the ER diagram.
1. A department employs many persons. A person is employed by, at most, one department.
2. A manager manages, at most, one department. A department is managed by, at most, one manager.
3. An author may write many books. A book may be written by many authors.
4. A team consists of many players. A player plays for only one team.
5. A lecturer teaches, at most, one course. A course is taught by exactly one lecturer.
6. A flight-leg connects two airports. An airport is used by many flight-legs.
7. A purchase order may be for many products. A product may appear on many purchase orders.
8. A customer may submit many orders. An order is for exactly one customer.
Help
To identify the entity types and relationships in each of the given pairs of rules, we can follow these steps:
1. Read the statements and identify the key entities involved.
2. Determine the relationship between the entities.
3. Assign appropriate cardinality to the relationship based on the given information.
Let's go through each pair and identify the entity types and relationships:
1. A department employs many persons. A person is employed by, at most, one department.
- Entity types: Department, Person
- Relationship: Employment
- Cardinality: One department employs many persons. A person can be employed by, at most, one department.
2. A manager manages, at most, one department. A department is managed by, at most, one manager.
- Entity types: Manager, Department
- Relationship: Management
- Cardinality: One manager manages, at most, one department. A department is managed by, at most, one manager.
3. An author may write many books. A book may be written by many authors.
- Entity types: Author, Book
- Relationship: Writing
- Cardinality: An author may write many books. A book may be written by many authors.
4. A team consists of many players. A player plays for only one team.
- Entity types: Team, Player
- Relationship: Participation
- Cardinality: One team consists of many players. A player plays for only one team.
5. A lecturer teaches, at most, one course. A course is taught by exactly one lecturer.
- Entity types: Lecturer, Course
- Relationship: Teaching
- Cardinality: One lecturer teaches, at most, one course. A course is taught by exactly one lecturer.
6. A flight-leg connects two airports. An airport is used by many flight-legs.
- Entity types: Flight-leg, Airport
- Relationship: Connection
- Cardinality: A flight-leg connects two airports. An airport is used by many flight-legs.
7. A purchase order may be for many products. A product may appear on many purchase orders.
- Entity types: Purchase Order, Product
- Relationship: Purchase
- Cardinality: A purchase order may be for many products. A product may appear on many purchase orders.
8. A customer may submit many orders. An order is for exactly one customer.
- Entity types: Customer, Order
- Relationship: Submission
- Cardinality: A customer may submit many orders. An order is for exactly one customer.
Based on the provided information, an ER diagram can be drawn to visually represent these relationships and entity types. Unfortunately, as a text-based AI, I cannot create visual diagrams. However, you can use any ER diagram tool or software to create the diagrams.