Determinant (computer science)

A determinant is a relational design theory term that deals with the conceptual design of the schemas of relational databases . The determinant describes the dependency between attributes of a relation . It defines which attribute sets determine the value of the other attributes.

definition

One or more attributes of a relational schema act as determinants if other attributes of the relational schema functionally depend on them ; so if and in each case a set of attributes of a relation schema , then is a determinant of when of functionally dependent (in characters ). A determinant is a condition that restricts the possible characteristics of a database schema, because if applies, then only such characteristics of are permitted for which the following applies: ${\ displaystyle A}$ ${\ displaystyle B}$ ${\ displaystyle R}$ ${\ displaystyle A}$ ${\ displaystyle B}$ ${\ displaystyle B}$ ${\ displaystyle A}$ ${\ displaystyle A \ rightarrow B}$ ${\ displaystyle A \ rightarrow B}$ ${\ displaystyle R}$

If two tuples have the same values for all attributes in , then the values of all attributes in both tuples must also match.

{\ displaystyle A}

{\ displaystyle B}

Determinants and keys

If determinant is thus within the relation all other attribute values by be determined, it means Super Key from . Furthermore, if ${\ displaystyle A}$ ${\ displaystyle R}$ ${\ displaystyle R}$ ${\ displaystyle A}$ ${\ displaystyle A}$ ${\ displaystyle R}$

${\ displaystyle A}$ is a determinant of and ${\ displaystyle R}$
${\ displaystyle A}$ is minimal

(in other words: is functionally dependent on, but not on a real subset of ), then is a key candidate or candidate keys , one of which can be selected as the primary key for . The scheme is then fully functionally dependent on . ${\ displaystyle R}$ ${\ displaystyle A}$ ${\ displaystyle A}$ ${\ displaystyle A}$ ${\ displaystyle R}$ ${\ displaystyle R}$ ${\ displaystyle A}$

literature

Alfons Kemper, André Eickler: Database systems. An introduction. Oldenbourg, Munich 2004, ISBN 3-486-27392-2 , page 163, 165f