In the context of database relationships, cardinality refers to the number of instances or entities that can be associated with another instance or entity in a relationship. It essentially defines how many records from one table are related to records in another table.

There are three commonly used cardinality types in database relationships:

1. One-to-One (1:1) Cardinality: This cardinality occurs when each record in one table is associated with exactly one record in another table, and vice versa. For example, let's consider a database schema for a university where each student is assigned a unique student ID, and this ID is associated with only one record in the "Student" table and vice versa.

2. One-to-Many (1:N) Cardinality: This cardinality occurs when each record in one table can be associated with multiple records in another table, but each record in the second table can only be associated with one record in the first table. For instance, in the same university database schema, each student can enroll in multiple courses, but each course can have only one associated student.

3. Many-to-Many (N:N) Cardinality: This cardinality occurs when each record in one table can be associated with multiple records in another table, and vice versa. In this case, an intermediary table is used to connect the two tables. To provide an example, in a bookstore database schema, each book can be written by multiple authors, and each author can write multiple books. Hence, an intermediary table is used to store the relationships between books and authors.

It is important to define and understand the cardinality of database relationships to ensure data integrity and accurate representation of real-world scenarios. Cardinality helps determine how tables are related and how data should be structured, avoiding data redundancy and inconsistency.

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