Default-all is dangerous!

TL;DR

The paper demonstrates that the default-all propagation scheme for database annotations can dangerously propagate irrelevant annotations, and proposes a safer, query-rewrite-insensitive alternative called minimum propagation.

Contribution

It introduces the minimum propagation scheme, a novel query-rewrite-insensitive method that accurately propagates only relevant annotations in database queries.

Findings

Default-all can propagate irrelevant annotations.

Minimum propagation is straightforward to evaluate.

Minimum propagation returns only relevant annotations.

Abstract

We show that the default-all propagation scheme for database annotations is dangerous. Dangerous here means that it can propagate annotations to the query output which are semantically irrelevant to the query the user asked. This is the result of considering all relationally equivalent queries and returning the union of their where-provenance in an attempt to define a propagation scheme that is insensitive to query rewriting. We propose an alternative query-rewrite-insensitive (QRI) where-provenance called minimum propagation. It is analogous to the minimum witness basis for why-provenance, straight-forward to evaluate, and returns all relevant and only relevant annotations.