This technical note presents the ubiquitous problem of query containment for conjunctive queries (an NP-complete problem), and an elegant implementation CQCP of Conjunctive Query Containment in Prolog, in just 7 lines of code. We also describe two important applications of conjunctive query containment: semantic query optimization and minimization. The latter can be implemented by another conci...

Hi-Desert Water District (HDWD), the primary water-management agency in the Warren Groundwater Basin, California, plans to construct a waste water treatment plant to reduce future septic-tank effluent from reaching the groundwater system. The treated waste water will be reclaimed by recharging the groundwater basin via recharge ponds as part of a larger conjunctive-use strategy. HDWD wishes to ...

This paper describes our submission to the TREC 2011 microblog task. For the experiments, we use our new self-index search engine, NeWT, to support ranked search in the Twitter document corpus. We use a combination of phrase queries and degrading conjunctive Boolean intersection to improve retrieval effectiveness. Keywords-self-index; full-text search, phrases, threshold; intersection

We study the use of SIMD instructions to support complex conjunctive numerical predicates. Compared to previous studies, we aim to model more realistic use scenarios, where different data types, different comparison operations, and different predicate types can be mixed in a single filtering clause. Moreover, the evaluation of the predicates on a set of columns can take advantage of multiple pr...

We study the data complexity of answering conjunctive queries over Description Logic knowledge bases constituted by a TBox and an ABox. In particular, we are interested in characterizing the FOrewritability and the polynomial tractability boundaries of conjunctive query answering, depending on the expressive power of the DL used to express the knowledge base. What emerges from our complexity an...

Conjunctive query answering is an important DL reasoning task. Although this task is by now quite well-understood, tight complexity bounds for conjunctive query answering in expressive DLs have never been obtained: all known algorithms run in deterministic double exponential time, but the existing lower bound is only an EXPTIME one. In this paper, we prove that conjunctive query answering in AL...

We show that, for OWL 2 QL ontology-mediated queries with (i) ontologies of bounded depth and conjunctive queries of bounded treewidth, (ii) ontologies of bounded depth and bounded-leaf tree-shaped conjunctive queries, and (iii) arbitrary ontologies and bounded-leaf tree-shaped conjunctive queries, one can construct and evaluate nonrecursive datalog rewritings by, respectively, LOGCFL, NL and L...

We investigate efficient enumeration algorithms for conjunctive queries for databases over binary relations that satisfy the X property. Tree-like relations such as XPath axes or grids are natural examples of such relations. We first show that the result of an n-ary conjunctive query Q over an X structure S can be enumerated with a delay in O(n·|S|·|Q|) between two consecutive n-tuples. Then, w...