Informally, two tuples are snapshot equivalent if the snapshots of the tuples at all times are identical.
Let temporal relation schema R have n time dimensions, Di, i = 1,…, n, and let τi, i = 1,…, n be corresponding timeslice operators, e.g., the valid timeslice and transaction timeslice operators. Then, formally, tuples x and y are snapshot equivalent if
| ∀t1∈D1…∀tn∈Dn( | |||
| *1cmτntn(…(τ1t1(x))…) = τntn(…(τ1t1(y))…)) . | |||
Similarly, two relations are snapshot equivalent if at every instant their snapshots are equal. Snapshot equivalence is a binary relation that can be applied to tuples and to relations.