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An Entity-Relationship Diagram (ERD) is a type of structural diagram used in database design. It visually represents the structure of a database, the different entities (or data objects) that will be stored in the database, the attributes those entities have, and the relationships between entities. |
Here's a breakdown of the key components of an ERD:
Entities: Entities are the main objects or concepts about which data is to be collected. For example, in a university database, entities might include "Students", "Courses", "Professors", etc. In an ERD, entities are typically represented as rectangles.
Attributes: Attributes are the properties or characteristics of entities. For the "Students" entity in a university database, attributes might include "Student ID", "Name", "Major", "Address", etc. In an ERD, attributes are represented as ovals connected to their respective entities.
Relationships: These represent how entities interact with each other. For instance, "Students" might have a relationship with "Courses" represented by the action "Enroll In". Relationships are shown as diamonds connecting entities in an ERD.
Cardinality: This refers to the numerical relationship between entities. For example, one "Student" can "Enroll In" multiple "Courses", but each "Course" can also have multiple "Students". These relationships can be one-to-one (1:1), one-to-many (1:M), or many-to-many (M:N).
Primary Key: This is a unique identifier for each record in an entity. For example, "Student ID" could be a primary key for the "Students" entity.
Foreign Key: This is an attribute that forms a link between the data in two tables. It's a field (or collection of fields) in one table, that is used to "refer" to the primary key in another table.
ERDs are critical in understanding the structure and architecture of a database. They help ensure that the final database is accurate, efficient, and meets the needs of the application or system it's designed to support.
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