Data relationship specifies the existence of information in one of the data extension columns, while the same information is contained in another column of some other data extension. The column is usually the primary key to one of the data extensions. In computer programming, tables are considered as data structures for the information organisation.

For example, a database that will enable people to book airline tickets should be created. Among the considered factors are the following airline services; airport code, plane number, seat number and a ticket number. All the four tables are related to a person, who has to identify which airline to travel with. In an airline, there are many planes and one travels with only one plane at a time. The seat number shows where exactly a person will sit while on board, and the ticket number serves as a proof for a flight booking. In this case, the airport code is the primary key because it will appear both on the ticket and at the airport as a person checks in.

The key aspect of producing a successful database is making sure that the reliability level of information enclosed in that the database is maintained in a constant trend. Therefore, data relationships are paramount in programming. Defining a relationship in the database design helps in grouping the fields, which contain related information. Organization of the tables and fields in order to reduce recurrence and dependency data is called normalization. A database that is not normalized contains recurring data in many fields, which may cause inconsistency. An un-normalized database may be tricky to use or fail to work as intended. One may consider creating an un-normalised database when the data used in a query is placed in one single table, lacking jeopardy of the data integrity.

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