The Impact of Disjunction on Query Answering Under Guarded-Based Existential Rules

These results have a important practical impact, since they make it possible to identify those sets of binary guarded existential rules for which it is possible to answer every

The chase procedure (or simply chase) is considered as one of the most fundamental algorithmic tools in databases — it accepts as input a database D and a set Σ of con- straints and,

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• Data complexity for QAtc and QAlin goes from PTIME to coNP-c. → Intuition: QAtc and QAlin can code disjunctive IDs QAtc: In T + (a, b) , is the T -path of length 1, 2,

For combined complexity, the membership problem for universal UCQ- solutions is 2E XP T IME -complete for Horn-ALCHI and Horn-ALCI; E XP T IME -com- plete for Horn-ALCH,

While in the combined complexity this task remains 2E XP T IME -complete, in case of fixed arity and fixed sets of rules, we observe the classical positive effect of restricting

For these sets of MDs a conjunctive query can be rewritten to retrieve, in polynomial time, the resolved answers, provided there are no joins on existentially quantified vari-

Since our rewriting algorithm is sound and complete (established by making use of the notion of chase), terminates under STGDs, and the rewritten query is a UCQs, answering