What Is a Functional Dependency?

As an important component in database normalization, database or functional dependency is a situation in which a value allows for the smooth transition to the next value in the sequence without any type of interruption. When this type of situation exists, the flow of information within the database proceeds without any type of delays or issues, and the integrity of the data itself is maintained. Functional dependency is essential in the creation and operation of relational databases, since the process involves the easy association with one value or type of data with other relevant values.

One of the easiest ways to understand how functional dependency works is to consider the use of a government-issued identification number, such as the Social Security number that is routinely issued to each citizen of the United States. By using this number as a means of identification, it is possible for employers to access information about the holder of that number; potential lenders and other creditors can utilize the number to access relevant financial information about an applicant, and the number makes it possible to access information such as taxes assessed and paid, income levels from one year to the next, and to calculate the government supported retirement benefits that the individual will eventually enjoy after leaving the work force. In many cases, employers may actually use this same number as the primary employee identification number or some section of the number as a relational tool to access the remainder of the employee’s electronic file.

Within the scope of database development and operation, functional dependency serves to allow users to enter some value that in turn can be used to retrieve the information that is desired. For example, a salesperson may enter the value of a company name in order to retrieve all records associated with contacts associated with a corporate customer. In like manner, salesperson who is planning a sales trip may enter a city name as the value as a means of accessing the names and contact information of all customers located near his or her destination, making it easier to arrange appointments with those clients.

While the exact structure of how a system provides functional dependency may vary based on the application involved, the end result is still the same. One value is related to another, making it possible to access the necessary information with relative ease. With so many records kept in databases rather than relying on the older method of hard copy files, this type of relational dependency is very important for locating and making use of relevant data.