Rank-Join Indices

Synonyms

Definition

Let R ₁ be a relation, over attributes A ₁ ¹, …, A _n ¹. We say that R ₁ is a ranked relation, if there is a designated rank attribute A _r ¹, with domain a subset of $\mathbb{R}^{+}$, such that the value A _r ¹(t) for tuple t defines the score of the tuple, and induces a ranking for the tuples in R ₁. Let R ₁, …, R _q be ranked relations. Without loss of generality, assume that A ₁ ¹, …, A ₁ ^q are the rank attributes, let θ be an arbitrary join condition defined between (sub)sets of the remaining attributes, and let $J(R_{1},\ldots,R_{q}) = (R_{1} \bowtie _{\theta _{1}}\ldots \bowtie _{\theta _{q-1}}R_{q})$ 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, …, s _q ) = (A ₁ ¹(t), …, A ₁ ^q(t)) of tuple t ∈ J(R ₁, …, R _q ), and produces a score value f(s ₁, …, s _q ) for the tuple t. A top-k join query asks for the ktuples...