systems analysis Systems analysis is "the process of studying a procedure or business to identify its goal and purposes and create systems and procedures that will efficiently achieve them". Another view sees system analysis as a problem-solving technique that b ...

, a one-to-one relationship is a type of

cardinality In mathematics, the cardinality of a set is a measure of the number of elements of the set. For example, the set A = \ contains 3 elements, and therefore A has a cardinality of 3. Beginning in the late 19th century, this concept was generalized ...

that refers to the relationship between two

entities An entity is something that exists as itself, as a subject or as an object, actually or potentially, concretely or abstractly, physically or not. It need not be of material existence. In particular, abstractions and legal fictions are usually ...

(see also

entity–relationship model An entity–relationship model (or ER model) describes interrelated things of interest in a specific domain of knowledge. A basic ER model is composed of entity types (which classify the things of interest) and specifies relationships that can ex ...

) A and B in which one element of A may only be linked to one element of B, and vice versa. In mathematical terms, there exists a

bijective In mathematics, a bijection, also known as a bijective function, one-to-one correspondence, or invertible function, is a function between the elements of two sets, where each element of one set is paired with exactly one element of the other s ...

function from A to B. For instance, think of A as the set of all human beings, and B as the set of all their brains. Any person from A can and must have only one brain from B, and any human brain in B can and must belong to only one person that is contained in A. In a

relational database A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relatio ...

, a one-to-one relationship exists when one row in a table may be linked with only one row in another table and vice versa. It is important to note that a one-to-one relationship is not a property of the data, but rather of the relationship itself. A list of mothers and their children may happen to describe mothers with only one child, in which case one row of the mothers table will refer to only one row of the children table and vice versa, but the relationship itself is not one-to-one, because mothers ''may'' have more than one child, thus forming a one-to-many relationship.

External links

Design pattern: many-to-many (order entry)
Tomjewett.com Data modeling {{systemstheory-stub

See also

External links