On database query languages for K-relations (original) (raw)

Abstract

The relational model has recently been extended to so-called K-relations in which tuples are assigned a unique value in a semiring K. A query language, denoted by RA C K , similar to the classical positive relational algebra, allows for the querying of K-relations. In this paper, we define more expressive query languages for K-relations, that extend RA C K to express operations on annotated tuples that are natural extensions of corresponding operations of the relational algebra, namely difference and constant annotations. We investigate conditions on semirings under which these operations can be added in a natural way, and establish basic properties of these query languages. Moreover, we show how the provenance semiring of Green et al. can be extended to record provenance of data in the presence of difference and constant annotations. Finally, we investigate completeness of RA C K and extensions thereof in the sense of Bancilhon and Paredaens (BP). K are already established in [11], less is known about its expressive power. Furthermore, it was left open in [11] how to incorporate difference in RA C K to get a full relational algebra on K-relations. Hence, our goal is twofold. On one hand, we define more expressive query languages for K-relations, that extend RA C K to express operations on annotated tuples that are natural extensions of corresponding operations of the relational algebra. On the other hand, we investigate completeness of RA C K and extensions thereof. Recall

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