arXiv subjects

Pan Hu

Publications and source records attributed to Pan Hu.

22 records · Page 2Linked to original sources

arXiv2019

Datalog Reasoning over Compressed RDF Knowledge Bases

Materialisation is often used in RDF systems as a preprocessing step to derive all facts implied by given RDF triples and rules. Although widely used, materialisation considers all possible rule applications and can use a lot of memory for storing the derived facts, which can hinder performance. We present a novel materialisation technique that compresses the RDF triples so that the rules can sometimes be applied to multiple facts at once, and the derived facts can be represented using structure sharing. Our technique can thus require less space, as well as skip certain rule applications. Our experiments show that our technique can be very effective: when the rules are relatively simple, our system is both faster and requires less memory than prominent state-of-the-art RDF systems.

cs.DB↗

arXiv2018

Modular Materialisation of Datalog Programs

The seminaïve algorithm can materialise all consequences of arbitrary datalog rules, and it also forms the basis for incremental algorithms that update a materialisation as the input facts change. Certain (combinations of) rules, however, can be handled much more efficiently using custom algorithms. To integrate such algorithms into a general reasoning approach that can handle arbitrary rules, we propose a modular framework for materialisation computation and its maintenance. We split a datalog program into modules that can be handled using specialised algorithms, and handle the remaining rules using the seminaïve algorithm. We also present two algorithms for computing the transitive and the symmetric-transitive closure of a relation that can be used within our framework. Finally, we show empirically that our framework can handle arbitrary datalog programs while outperforming existing approaches, often by orders of magnitude.

cs.AI↗

arXiv2017

Optimised Maintenance of Datalog Materialisations

To efficiently answer queries, datalog systems often materialise all consequences of a datalog program, so the materialisation must be updated whenever the input facts change. Several solutions to the materialisation update problem have been proposed. The Delete/Rederive (DRed) and the Backward/Forward (B/F) algorithms solve this problem for general datalog, but both contain steps that evaluate rules 'backwards' by matching their heads to a fact and evaluating the partially instantiated rule bodies as queries. We show that this can be a considerable source of overhead even on very small updates. In contrast, the Counting algorithm does not evaluate the rules 'backwards', but it can handle only nonrecursive rules. We present two hybrid approaches that combine DRed and B/F with Counting so as to reduce or even eliminate 'backward' rule evaluation while still handling arbitrary datalog programs. We show empirically that our hybrid algorithms are usually significantly faster than existing approaches, sometimes by orders of magnitude.

cs.DB↗

arXiv2017

Effects of internal asymmetry on interface curvatures and outer drags determining the oriented shift of the eccentric globules

The physical mechanism of the oriented shift and inverse of eccentric globules in a modest extensional flow are investigated in this paper. Through this work, a shift of the globule, which is driven mainly by the asymmetric interfacial curvature, not by the outer drag, is disclosed. The asymmetric layout of the daughter droplet leads to the asymmetric drags from the continuous phase and the asymmetric deformation of the globule with different interface curvatures. As the inner droplet has both enhancing and suppressing effect on the globule deformation, the interface curvatures will vary when changing the relative size and location of the inner droplet. This curvature difference results in the asymmetric pressure distribution and circulation inside the globule. Eventually, the interaction of the inner driving force (pressure differences) and the outer drags causes the oriented shift and inverse of the globule. The shift direction is affected not only by the structural asymmetry parameter (eccentricity), but also by some flow features such as the capillary number. The results obtained here might enlighten potential applications for the movement of soft globules driven by curvature differences.

cond-mat.soft↗