Matching Top-k Answers of Twig Patterns in Probabilistic XML

The flexibility of XML data model allows a more natural representation of uncertain data compared with the relational model. The top-k matching of a twig pattern against probabilistic XML data is essential. Some classical twig pattern algorithms can be adjusted to process the probabilistic XML. However, as far as finding answers of the top-k probabilities is concerned, the existing algorithms suffer in performance, because many unnecessary intermediate path results, with small probabilities, need to be processed. To cope with this problem, we propose a new encoding scheme called PEDewey for probabilistic XML in this paper. Based on this encoding scheme, we then design two algorithms for finding answers of top-k probabilities for twig queries. One is called ProTJFast, to process probabilistic XML data based on element streams in document order, and the other is called PTopKTwig, based on the element streams ordered by the path probability values. Experiments have been conducted to study the performance of these algorithms.