Characterizing and Computing Causes for Query Answers in Databases from Database Repairs and Repair Programs

Abstract

A correspondence between database tuples as causes for query answers in databases and tuple-based repairs of inconsistent databases with respect to denial constraints has already been established. In this work, answerset programs that specify repairs of databases are used as a basis for solving computational and reasoning problems about causes. Here, causes are also introduced at the attribute level by appealing to a both null-based and attributebased repair semantics. The corresponding repair programs are presented, and they are used as a basis for computation and reasoning about attribute-level causes. They are extended to deal with the case of causality under integrity constraints. Several examples with the DLV system are shown.

Repair-Based Degrees of Database Inconsistency

“…The same applies to the use of the inconsistency measure to explore the causes for inconsistency, in particular, to analyze how it changes when tuples or combinations thereof are removed from the database. Such an application sounds natural given the established connection between database repairs, causality and causal responsibility [11,6].…”

“…Similar repair programs can be produced to specify attribute-based repairs that, instead of deleting (or inserting) tuples, change attribute values in existing tuples. This is the case, for example, when one allows changing values into a null value as in SQL databases, on the assumption that joins and comparisons through nulls do not hold [6]. This becomes relevant in Section 7.…”

“…The connection between database causality and database repairs was established and exploited for causality purposes in[11,6].…”

“…In this particular case, it might be better to use |D n | 8. This approach was followed in[6] to compute maximum responsibility degrees of database tuples as causes for violations of DCs, appealing to a causality-repair connection[11].…”

Measuring and Computing Database Inconsistency via Repairs

“…Σ and dist (D, {D}) = 0, a consistent instance D should have 0 as inconsistency degree. 1 Notice that the class Rep S (D, Σ) might contain instances that are not sub-instances of D, for example, for different forms of inclusion dependencies (INDs) we may want to insert tuples; 2 or even under DCs, we may want to appeal to attribute-based repairs. In the following we consider only repairs that are sub-instances of the given instance.…”