4tuple

A 4-tuple, also called a quadruple, is an ordered collection of four elements. If A, B, C, and D are sets, a 4-tuple is an element of the Cartesian product A × B × C × D and is typically written as (a, b, c, d) with a ∈ A, b ∈ B, c ∈ C, and d ∈ D. The order of the components matters, and repetition of elements is allowed unless stated otherwise. Two 4-tuples are equal only if each corresponding component is equal.

In mathematics, 4-tuples arise in various contexts, including coordinates in four-dimensional space and representations of algebraic structures with four components. They also appear as data encodings for relations of arity four and as a basic building block in higher-dimensional constructions.

In computer science and databases, a 4-tuple can serve as a record with four fields. A database relation with four attributes has rows that are 4-tuples, one per record. In programming, a 4-tuple can be used to return or store related values that do not naturally form a single composite type, providing a simple way to group four heterogeneous components.

In networking and security, the term 4-tuple is often used for the connection identifier consisting of (source IP, destination IP, source port, destination port). This 4-tuple uniquely identifies a network connection as traffic traverses a network, and it is a common concept in firewall rules and traffic analysis.