Enhanced Entity Relationship Model (EER Model)
What is Enhanced Entity Relationship (EER) Model?
Enhanced Entity Relationship (EER) Model is a data model that provides a more expressive and powerful way to represent the data and relationships in a database. It is a refinement of the Entity Relationship (ER) Model, which is a popular data model used to design database systems.
The main purpose of the EER Model is to capture the rich semantics of the real world in a more precise and comprehensive way than the basic ER Model. It allows designers to represent complex relationships, constraints, and business rules more accurately and completely.
The role of the EER Model is to serve as a high-level conceptual model that provides a clear and intuitive understanding of the data and relationships in the system. It is used to communicate the design of a database system to stakeholders, such as database administrators, developers, and users.
The importance of the EER Model lies in its ability to represent complex real-world scenarios in a structured and meaningful way. It helps designers to identify the entities and relationships in the system, and to understand how they are related to each other. This enables designers to create a more accurate and comprehensive database design that meets the needs of the users.
The main components of the EER Model are:
- Entity types: These represent the real-world objects or concepts in the system, such as customers, orders, or products.
- Attributes: These represent the properties or characteristics of the entity types, such as name, address, or price.
- Relationships: These represent the associations or connections between entity types, such as a customer placing an order, or an order containing multiple products.
- Inheritance: This is a feature of the EER Model that allows a subclass to inherit the attributes and relationships of its superclass.
- Specialization and generalization: These are two types of inheritance that allow designers to represent hierarchical relationships between entity types. Specialization represents a more specific entity type that is derived from a more general entity type, while generalization represents a more general entity type that is derived from multiple more specific entity types.
Here is an example of an EER Model for a simple online store:
- Entity types: Customer, Order, Product
- Attributes: Customer - name, address, email; Order - order number, order date, total cost; Product - product id, product name, unit price
- A customer places one or more orders (one-to-many)
- An order consists of one or more products (one-to-many)
- Physical product (specialization of Product) - attributes: weight, dimensions
- Digital product (specialization of Product) - attributes: file size, download link
The EER Model also includes a number of advanced modeling concepts that allow designers to represent more complex scenarios. These include:
- Aggregation: This is a relationship between two entity types, where one entity type contains the other entity type as a part. For example, in an EER Model for a car dealership, the entity type "Car" might be aggregated by the entity type "Dealership," to represent the fact that a dealership has a collection of cars.
- Association classes: These are additional entity types that are used to represent additional attributes or relationships that exist between two entity types. For example, in an EER Model for a library, an association class might be used to represent the attributes of a book loan, such as the loan date and the due date.
- Weak entity types: These are entity types that do not have a unique identifier of their own, and are instead identified by their relationship with another entity type. For example, in an EER Model for a school, a weak entity type "Enrollment" might be used to represent the relationship between a student and a course, with the student's enrollment being identified by the combination of their student ID, and the course ID.
- N-ary relationships: These are relationships between three or more entity types. For example, in an EER Model for a university, an n-ary relationship might be used to represent the relationship between a student, a course, and a professor, to represent the fact that a student is enrolled in a course that is taught by a particular professor.
The EER Model is a powerful and flexible tool for designing database systems and is widely used in a variety of applications, including business, finance, healthcare, and education. It provides a clear and intuitive way to represent the data and relationships in a system and helps designers to create more accurate and comprehensive database designs.