Synonyms
Equality-generating dependency (egd)
Definition
Tuple-generating dependencies, or tgds, are one of the two major types of database dependencies (the other major type consists of equality-generating dependencies, or egds).
To define tgds, the notion of an atomic formula is first needed, which is a formula of the form P(x 1,...,x k ), where P is a k-ary relational symbol, and x 1,...,x k are variables, not necessarily distinct.
Then tgds are formulas of the form ∀x(φ(x) →∃y ψ(x, y)), where
- 1.
φ(x) is a conjunction of atomic formulas, all with variables among the variables in x.
- 2.
every variable in x appears in φ(x) (but not necessarily in ψ(x, y)).
- 3.
ψ(x, y) is a conjunction of atomic formulas, all with variables among the variables in x and y.
If y is empty, so that there are no existentially-quantified variables, then the tgd is called full.
Conditions (1) and (2) together are sometimes replaced by the weaker condition that φ(x) be an arbitrary first-order formula with free...
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Fagin, R. (2009). Tuple-Generating Dependencies. In: LIU, L., ÖZSU, M.T. (eds) Encyclopedia of Database Systems. Springer, Boston, MA. https://doi.org/10.1007/978-0-387-39940-9_1274
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DOI: https://doi.org/10.1007/978-0-387-39940-9_1274
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