Podcast
Questions and Answers
What is the primary purpose of an Entity-Relationship model?
What is the primary purpose of an Entity-Relationship model?
- To visualize data relationships
- To design a database schema (correct)
- To analyze data queries
- To implement a database
What are the components that an ER model is based on?
What are the components that an ER model is based on?
- Entities and relationships
- Attributes and constraints
- Entities, relationships, and dependencies
- Entities, attributes, and constraints (correct)
What is an entity in the context of an ER model?
What is an entity in the context of an ER model?
- A constraint on a database design
- A specific object or thing in the mini-world (correct)
- A relationship between objects
- A property of an object
What is an attribute in the context of an ER model?
What is an attribute in the context of an ER model?
In the COMPANY database, what is a department composed of?
In the COMPANY database, what is a department composed of?
What is a Relationship Type?
What is a Relationship Type?
What is tracked for each employee in the COMPANY database?
What is tracked for each employee in the COMPANY database?
What is the purpose of an Entity-Relationship Diagram (ER Diagram)?
What is the purpose of an Entity-Relationship Diagram (ER Diagram)?
What is represented by a diamond-shaped box in an ER diagram?
What is represented by a diamond-shaped box in an ER diagram?
How many relationship types are identified in the refined COMPANY database schema?
How many relationship types are identified in the refined COMPANY database schema?
What is a project in the COMPANY database?
What is a project in the COMPANY database?
What is the degree of the relationships identified in the refined COMPANY database schema?
What is the degree of the relationships identified in the refined COMPANY database schema?
What is the popular name for the VehicleIdentificationNumber attribute?
What is the popular name for the VehicleIdentificationNumber attribute?
What is the relationship type between an EMPLOYEE and a DEPARTMENT in the refined COMPANY database schema?
What is the relationship type between an EMPLOYEE and a DEPARTMENT in the refined COMPANY database schema?
What happens to the attribute 'Manager of DEPARTMENT' in the refined design?
What happens to the attribute 'Manager of DEPARTMENT' in the refined design?
How are attributes typically displayed in an ER diagram?
How are attributes typically displayed in an ER diagram?
What is the purpose of underlining a key attribute in an ER diagram?
What is the purpose of underlining a key attribute in an ER diagram?
What is possible between the same participating entity types?
What is possible between the same participating entity types?
What is the relationship type between a PROJECT and a DEPARTMENT in the refined COMPANY database schema?
What is the relationship type between a PROJECT and a DEPARTMENT in the refined COMPANY database schema?
What is an entity set?
What is an entity set?
How many initial entity types are identified for the COMPANY database?
How many initial entity types are identified for the COMPANY database?
What is the name of the employee who manages a department?
What is the name of the employee who manages a department?
What does a department control in the COMPANY database?
What does a department control in the COMPANY database?
What is the purpose of an ER diagram?
What is the purpose of an ER diagram?
Study Notes
ER Model
- An Entity-Relationship (ER) model describes the structure of a database with the help of a diagram, known as an Entity-Relationship Diagram (ER Diagram).
- An ER model is a design or blueprint of a database that can later be implemented as a database.
- ER Model is based on the notion of real-world entities and relationships among them.
- ER Model is best used for the conceptual design of a database.
ER Model Components
- Entities and their attributes
- Constraints
- Relationships among entities
ER Diagram
- Entity types are displayed in rectangular boxes
- Attributes are displayed in ovals
- Each attribute is connected to its entity type
- Components of a composite attribute are connected to the oval representing the composite attribute
- Each key attribute is underlined
- Multivalued attributes are displayed in double ovals
Entity Set
- Each entity type will have a collection of entities stored in the database
- Called the entity set
- The entity set is the current state of the entities of that type that are stored in the database
Entity Types in the COMPANY Database
- DEPARTMENT
- PROJECT
- EMPLOYEE
- DEPENDENT
Attributes for Each Entity Type
- DEPARTMENT: name, number, employee who manages the department, start date of the department manager, locations
- PROJECT: unique name, unique number, location
- EMPLOYEE: social security number, address, salary, sex, birthdate, department, projects, number of hours per week worked on each project, direct supervisor
- DEPENDENT: name, sex, birthdate, relationship to the employee
Relationship Types
- Is the schema description of a relationship
- Identifies the relationship name and the participating entity types
- Identifies certain relationship constraints
Relationship Sets
- The current set of relationship instances represented in the database
- The current state of a relationship type
Relationship Types in the COMPANY Database
- WORKS_FOR (between EMPLOYEE, DEPARTMENT)
- MANAGES (between EMPLOYEE, DEPARTMENT)
- CONTROLS (between DEPARTMENT, PROJECT)
- WORKS_ON (between EMPLOYEE, PROJECT)
- SUPERVISION (between EMPLOYEE (as subordinate), EMPLOYEE (as supervisor))
- DEPENDENTS_OF (between EMPLOYEE, DEPENDENT)
ER Diagram – Relationship Types
- WORKS_FOR, MANAGES, WORKS_ON, CONTROLS, SUPERVISION, DEPENDENTS_OF
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Description
Learn about the Entity-Relationship model, a design blueprint for databases that represents real-world entities and their relationships. Understand how to create an ER diagram and implement a database.
