Finding Patterns in a Knowledge Base using Keywords to Compose Table Answers

We aim to provide table answers to keyword queries against knowledge bases. For queries referring to multiple entities, like "Washington cities population" and "Mel Gibson movies", it is better to represent each relevant answer as a table which aggregates a set of entities or entity-joins within the same table scheme or pattern. In this paper, we study how to find highly relevant patterns in a knowledge base for user-given keyword queries to compose table answers. A knowledge base can be modeled as a directed graph called knowledge graph, where nodes represent entities in the knowledge base and edges represent the relationships among them. Each node/edge is labeled with type and text. A pattern is an aggregation of subtrees which contain all keywords in the texts and have the same structure and types on node/edges. We propose efficient algorithms to find patterns that are relevant to the query for a class of scoring functions. We show the hardness of the problem in theory, and propose path-based indexes that are affordable in memory. Two query-processing algorithms are proposed: one is fast in practice for small queries (with small patterns as answers) by utilizing the indexes; and the other one is better in theory, with running time linear in the sizes of indexes and answers, which can handle large queries better. We also conduct extensive experimental study to compare our approaches with a naive adaption of known techniques.Comment: VLDB 201

Accretion Flow Properties of EXO 1846-031 During its Multi-Peaked Outburst After Long Quiescence

We study the recent outburst of the black hole candidate EXO 1846-031 which went into an outburst in 2019 after almost 34 years in quiescence. We use archival data from Swift/XRT, MAXI/GSC, NICER/XTI and NuSTAR/FPM satellites/instruments to study the evolution of the spectral and temporal properties of the source during the outburst. Low energy X-ray flux of the outburst shows multiple peaks making it a multipeak outburst. Evolving type-C quasi-periodic oscillations (QPOs) are observed in the NICER data in the hard, hard intermediate and soft intermediate states. We use the physical Two Component Advective Flow (TCAF) model to analyze the combined spectra of multiple satellite instruments. According to the TCAF model, the accreting matter is divided into Keplerian and sub-Keplerian parts, and the variation in the observed spectra in different spectral states arises out of the variable contributions of these two types of accreting matter in the total accretion rate. Studying the evolution of the accretion rates and other properties of the accretion flow obtained from the spectral analysis, we show how the multiple peaks in the outburst flux arises out of discontinuous supply and different radial velocities of two types of accreting matter from the pile-up radius. We detect an Fe emission line at $\sim6.6$ keV in the hard and the intermediate states in the NICER spectra. We determine the probable mass of the black hole to be $12.43^{+0.14}_{-0.03}~M_\odot$ from the spectral analysis with the TCAF model. We also estimate viscous time scale of the source in this outburst to be $\sim 8$ days from the peak difference of the Keplerian and sub-Keplerian mass accretion rates.Comment: 15 pages, 8 Figures, 2 Tables (In Communication ApJ

Ranking objects by exploiting relationships: computing top-k over aggregation

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