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In this paper we study the problem of mining all frequent queries in a given database table, a problem known to be intractable even for conjunctive queries. We restrict our attention to projection-selection queries, and we assume that the table to be mined satisfies a set of functional dependencies. Under these assumptions we define a pre-ordering over queries and we show the following: (a) the support measure is anti-monotonic (with respect to ), and (b) if we define q ≡ q ′ iff q q ′ and q ′ q then all queries of an equivalence class have the same support.With these results at hand, we further restrict our attention to star schemas of data warehouses. In those schemas, the set of functional dependencies satisfies an important property, namely, the union of keys of all dimension tables is a key for the fact table. The main contribution of this paper is the proposal of a level-wise algorithm for mining all frequent projection-selection queries in a data warehouse over a star schema. Moreover, we show that, in the case of a star schema, the complexity in the number of scans of our algorithm is similar to that of the well known Apriori algorithm, i.e., linear with respect to the number of attributes.

No abstract

International audienc

International audienc