The volume of RDF data continues to grow over the past decade and many known RDF datasets have billions of triples. A grant challenge of managing this huge RDF data is how to access this big RDF data efficiently. A popular approach to addressing the problem is to build a full set of permutations of (S, P, O) indexes. Although this approach has shown to accelerate joins by orders of magnitude, the large space overhead limits the scalability of this approach and makes it heavyweight. In this paper, we present TripleBit, a fast and compact system for storing and accessing RDF data. The design of TripleBit has three salient features. First, the compact design of TripleBit reduces both the size of stored RDF data and the size of its indexes. Second, TripleBit introduces two auxiliary index structures, ID-Chunk bit matrix and ID-Predicate bit matrix, to minimize the cost of index selection during query evaluation. Third, its query processor dynamically generates an optimal execution ordering for join queries, leading to fast query execution and effective reduction on the size of intermediate results. Our experiments show that TripleBit outperforms RDF-3X, MonetDB, BitMat on LUBM, UniProt and BTC 2012 benchmark queries and it offers orders of mangnitude performance improvement for some complex join queries.
Abstract-The emerging need for conducting complex analysis over big RDF datasets calls for scale-out solutions that can harness a computing cluster to process big RDF datasets. Queries over RDF data often involve complex self-joins, which would be very expensive to run if the data are not carefully partitioned across the cluster and hence distributed joins over massive amount of data are necessary. Existing RDF data partitioning methods can nicely localize simple queries but still need to resort to expensive distributed joins for more complex queries. In this paper, we propose a new data partitioning approach that takes use of the rich structural information in RDF datasets and minimizes the amount of data that have to be joined across different computing nodes. We conduct an extensive experimental study using two popular RDF benchmark data and one real RDF dataset that contain up to billions of RDF triples. The results indicate that our approach can produce a balanced and low redundant data partitioning scheme that can avoid or largely reduce the cost of distributed joins even for very complicated queries. In terms of query execution time, our approach can outperform the state-of-the-art methods by orders of magnitude.
Text objects occurring in image can provide much useful information for content based information retrieval and counting applications, because they contain much minute information related to the documents contents. However, extracting text from images and videos is a very difficult task due to the varying font, size, color, orientation, and malformation of text objects. Although a large number of text extraction approaches have been reported in the past work, no specific designed text model and character features are presented to capture the unique properties and structure of characters and text objects. We have proposed SVM, KNN and NN Techniques in our research. The thesis was focused on the design of an algorithm to detect the text from images, extract it and convert it into speech for those who are unable to read and its implementation on MATLAB.
Abstract-Large scale graph processing represents an interesting systems challenge due to the lack of locality. This paper presents PathGraph, a system for improving iterative graph computation on graphs with billions of edges. Our system design has three unique features: First, we model a large graph using a collection of tree-based partitions and use pathcentric computation rather than vertex-centric or edge-centric computation. Our path-centric graph parallel computation model significantly improves the memory and disk locality for iterative computation algorithms on large graphs. Second, we design a compact storage that is optimized for iterative graph parallel computation. Concretely, we use delta-compression, partition a large graph into tree-based partitions and store trees in a DFS order. By clustering highly correlated paths together, we further maximize sequential access and minimize random access on storage media. Third but not the least, we implement the path-centric computation model by using a scatter/gather programming model, which parallels the iterative computation at partition tree level and performs sequential local updates for vertices in each tree partition to improve the convergence speed. We compare PathGraph to most recent alternative graph processing systems such as GraphChi and X-Stream, and show that the path-centric approach outperforms vertex-centric and edge-centric systems on a number of graph algorithms for both in-memory and out-of-core graphs.
In recent years, systems researchers have devoted considerable effort to the study of large-scale graph processing. Existing distributed graph processing systems such as Pregel, based solely on distributed memory for their computations, fail to provide seamless scalability when the graph data and their intermediate computational results no longer fit into the memory; and most distributed approaches for iterative graph computations do not consider utilizing secondary storage a viable solution. This paper presents GraphMap, a distributed iterative graph computation framework that maximizes access locality and speeds up distributed iterative graph computations by effectively utilizing secondary storage. GraphMap has three salient features: (1) It distinguishes data states that are mutable during iterative computations from those that are read-only in all iterations to maximize sequential access and minimize random access. (2) It entails a two-level graph partitioning algorithm that enables balanced workloads and locality-optimized data placement. (3) It contains a proposed suite of locality-based optimizations that improve computational efficiency. Extensive experiments on several real-world graphs show that GraphMap outperforms existing distributed memory-based systems for various iterative graph algorithms.
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