Explain the use of cardinality 

Cardinality in database design refers to the relationship between tables or entities and indicates how many instances of one entity relate to instances of another. It plays a key role in defining the structure and integrity of the database. Cardinality is used in several contexts:

1. **Entity Relationships:** Specifies the number of instances of one entity that can or must be associated with instances of another entity. Common types include:

   - **One-to-One (1:1):** Each record in one table corresponds to exactly one record in another table.

   - **One-to-Many (1:N):** A single record in one table can relate to multiple records in another table.

   - **Many-to-Many (M:N):** Multiple records in one table can relate to multiple records in another table, often requiring a junction table.

2. **Data Integrity:** Ensures that relationships between entities are consistent and adheres to defined constraints, such as referential integrity.

3. **Database Design:** Helps in designing efficient schema structures by defining how tables are related, which affects how data is queried and maintained.

4. **Query Optimization:** Impacts how queries are formulated and optimized, influencing performance and efficiency.

Understanding and defining cardinality correctly is crucial for creating a well-structured, efficient, and reliable database schema.