What do you mean by a self-referencing foreign key? Explain with the help of an example.

Integrity constraints are the rules defined on a relational database schema and satisfied by all the instances of database in order to model the real-world concepts correctly. They ensure the consistency of database while the modifications are made by the users. For example, the integrity constraint ensures that the value of ISBN in BOOK relation cannot be duplicated or null.

A database can be defined as a collection of related data from which users can efficiently retrieve the desired information. A database can be anything from a simple collection of roll numbers, names, addresses and phone numbers of students to a complex collection of sound, images and even video or film clippings. Though databases are generally computerized, instances of non-computerized databases from everyday life can be cited in abundance. A dictionary, a phone book, a collection of recipes and a TV guide are examples of non-computerized databases. The examples of computerized databases include customer files, employee rosters, books catalog, equipment inventories and sales transactions.

A Database Management System (DBMS) is an integrated set of programs used to create and maintain a database. The main objective of a DBMS is to provide a convenient and effective method of defining, storing, retrieving and manipulating the data contained in the database.

To provide a high degree of data independence, the definition or the description of the database structure (structure of each file, the type and storage format of each data item) and various constraints on the data are stored separately in a table. This table is known as the DBMS catalog. The information contained in the catalog is called the metadata (data about data).

The property of DBMS that allows program-data independence is known as data abstraction. Data abstraction allows the database system to provide an abstract view of the data to its users without giving the physical storage and implementation details.