Can One Escape Red Chains?

On Monotonic Determinacy and Rewritability for Recursive Queries and Views

“…For specialized recursive queries and views over a graph schema, the regular path queries, both the determinacy and monotonic determinacy problem have been studied. For one-and two-way regular path queries and views monotonic determinacy (aka "losslessness with respect to the sound view assumption") is decidable in ExpSpace ( [10] for 1-way, [11] for 2-way), and implies Datalog rewritability [15], while plain determinacy is undecidable [16]. It follows from [14] that monotonic determinacy is undecidable for Datalog queries and CQ views and implies rewritability in Datalog over views.…”

“…For our positive results, a key tool is an automata-theoretic technique, involving bounds on the treewidth of view images and the forward-backward method developed for analysis of guarded logics [8,19]. For our negative results, we show how to adapt some of the coding ideas used in showing undecidability of determinacy [16][17][18] to the setting of monotonic determinacy, and we also show how tools from constraint satisfaction [4] can be used to provide monotonically-determined queries that have no Datalog rewriting.…”