Preserving Constraints with the Stable Chase

Talk by Maximilian Marx

Location: APB 3027
Start: 8. March 2018 at 9:20 am
End: 8. March 2018 at 10:50 am
Research group: Knowledge-Based Systems
Event series: KBS Seminar
iCal

Conjunctive query answering over databases with constraints – also known as (tuple-generating)

dependencies – is considered a central database task. To this end, several versions of a con- struction called chase have been described. Given a set Σ of dependencies, it is interesting to ask which constraints not contained in Σ that are initially satisfied in a given database instance are preserved when computing a chase over Σ. Such constraints are an example for the more general class of incidental constraints, which when added to Σ as new dependencies do not affect certain answers and might even speed up query answering. After formally introducing incidental constraints, we show that deciding incidentality is undecidable for tuple-generating dependencies, even in cases for which query entailment is decidable. For dependency sets with a finite universal model, the core chase can be used to decide incidentality. For the infinite case, we propose the

stable chase, which generalises the core chase, and study its relation to incidental constraints.