Question :
What is cardinality in data modeling?
Subject
Software Engineering
Standard
Computer Science Engineering
Views
629
Asked By
Knowledge
Anaisha
Answer / Solution
Answer / Solution
In data modeling, cardinality refers to the relationship between two entities. There are three types of cardinality:
- One-to-one: Each row in the first table can be related to only one row in the second table. For example, a table of employees might have a one-to-one relationship with a table of employee salaries. Each employee would have only one salary, and each salary would be associated with only one employee.
- One-to-many: Each row in the first table can be related to zero or more rows in the second table. For example, a table of products might have a one-to-many relationship with a table of orders. Each product can be ordered multiple times, but each order will only have one product.
- Many-to-many: Each row in the first table can be related to zero or more rows in the second table, and vice versa. For example, a table of students might have a many-to-many relationship with a table of courses. Each student can take multiple courses, and each course can be taken by multiple students.
Cardinality is important for data modeling because it helps to ensure that the data in the database is consistent. For example, if a table has a one-to-one relationship with another table, then it is not possible for a row in the first table to be related to more than one row in the second table. This helps to ensure that the data in the database is accurate and reliable.
Cardinality can be represented visually using entity-relationship diagrams (ERDs). An ERD is a graphical representation of a database schema. In an ERD, cardinality is represented by a line connecting two entities. The type of cardinality is indicated by the shape of the end of the line. For example, a one-to-one relationship is represented by a line with a diamond at one end. A one-to-many relationship is represented by a line with a crow's foot at one end. A many-to-many relationship is represented by a line with two crow's feet.
Cardinality is an important concept in data modeling. It helps to ensure that the data in the database is consistent and accurate. By understanding cardinality, you can create better data models that will support your business needs.
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