Rank-Join Indices

Synonyms

Skyline queries; Top-k queries

Definition

Let R₁ be a relation, over attributes $A^1_1,\ldots , A^1_n$. We say that R₁ is a ranked relation, if there is a designated rank attribute$A^1_r$, with domain a subset of $\mathbb {R}^{+}$, such that the value $A^1_r(t)$ for tuple t defines the score of the tuple, and induces a ranking for the tuples in R₁. Let R₁, …, R_q be ranked relations. Without loss of generality, assume that $A^1_1,\ldots ,A^q_1$ are the rank attributes, let θ be an arbitrary join condition defined between (sub)sets of the remaining attributes, and let $J(R_1,\ldots ,R_q) = (R_1 \Join _{{\theta }_1} \ldots \Join _{{\theta }_{q-1}} R_q )$ denote the resulting relation. Let $f: \mathbb {R}^{+} \times \ldots \times \mathbb {R}^{+} \rightarrow \mathbb {R}^{+}$ be a scoring function that takes as input the rank attribute values $(s_1,\ldots ,s_q) = (A^1_1(t),\ldots ,A^q_1(t))$ of tuple t ∈ J(R₁, …, R_q), and produces a score value f(s₁, …, s_q) for the...