What is the importance of constraints in a physical model? What role do different constraints play in maintaining referential integrity and data integrity?

Answer with Explanation:

Constraints are a very important feature in a relational model. Constraints are useful because they allow a designer to specify the semantics of data in the database. They are the rules that force Database Management Systems (DBMSs) to check that data satisfies the semantics.

Data integrity is the overall completeness, accuracy and consistency of data. This can be indicated by the absence of alteration between two instances or between two updates of a data record, meaning data is intact and unchanged

Referential integrity (RI) is a method for ensuring the "correctness" of data within a Database Management System. It embodies the integrity and usability of a relationship by establishing rules that govern that relationship.

Proper database RI ensures data integrity for both planned application programs and for queries in ad hoc SQL statements and BI tools.

By defining referential constraints, you can set up the database to control the semantic accuracy of the data it contains. To define a referential constraint, you must create a primary key in the parent table and a foreign key in the dependent table.

You must also define what actions are allowed when data is added or modified. This is accomplished with a set of rules applied to each relationship. The combination of the primary and foreign key columns and the rules that dictate the data that can be housed in those key columns can be defined to ensure correct and useful relational databases.

So, it is a good physical database design practice to implement referential integrity using database constraints.