4,540 research outputs found
Shared Arrangements: practical inter-query sharing for streaming dataflows
Current systems for data-parallel, incremental processing and view
maintenance over high-rate streams isolate the execution of independent
queries. This creates unwanted redundancy and overhead in the presence of
concurrent incrementally maintained queries: each query must independently
maintain the same indexed state over the same input streams, and new queries
must build this state from scratch before they can begin to emit their first
results. This paper introduces shared arrangements: indexed views of maintained
state that allow concurrent queries to reuse the same in-memory state without
compromising data-parallel performance and scaling. We implement shared
arrangements in a modern stream processor and show order-of-magnitude
improvements in query response time and resource consumption for interactive
queries against high-throughput streams, while also significantly improving
performance in other domains including business analytics, graph processing,
and program analysis
Reasoning & Querying – State of the Art
Various query languages for Web and Semantic Web data, both for practical use and as an area of research in the scientific community, have emerged in recent years. At the same time, the broad adoption of the internet where keyword search is used in many applications, e.g. search engines, has familiarized casual users with using keyword queries to retrieve information on the internet. Unlike this easy-to-use querying, traditional query languages require knowledge of the language itself as well as of the data to be queried. Keyword-based query languages for XML and RDF bridge the gap between the two, aiming at enabling simple querying of semi-structured data, which is relevant e.g. in the context of the emerging Semantic Web. This article presents an overview of the field of keyword querying for XML and RDF
Four Lessons in Versatility or How Query Languages Adapt to the Web
Exposing not only human-centered information, but machine-processable data on the Web is one of the commonalities of recent Web trends. It has enabled a new kind of applications and businesses where the data is used in ways not foreseen by the data providers. Yet this exposition has fractured the Web into islands of data, each in different Web formats: Some providers choose XML, others RDF, again others JSON or OWL, for their data, even in similar domains. This fracturing stifles innovation as application builders have to cope not only with one Web stack (e.g., XML technology) but with several ones, each of considerable complexity. With Xcerpt we have developed a rule- and pattern based query language that aims to give shield application builders from much of this complexity: In a single query language XML and RDF data can be accessed, processed, combined, and re-published. Though the need for combined access to XML and RDF data has been recognized in previous work (including the W3C’s GRDDL), our approach differs in four main aspects: (1) We provide a single language (rather than two separate or embedded languages), thus minimizing the conceptual overhead of dealing with disparate data formats. (2) Both the declarative (logic-based) and the operational semantics are unified in that they apply for querying XML and RDF in the same way. (3) We show that the resulting query language can be implemented reusing traditional database technology, if desirable. Nevertheless, we also give a unified evaluation approach based on interval labelings of graphs that is at least as fast as existing approaches for tree-shaped XML data, yet provides linear time and space querying also for many RDF graphs. We believe that Web query languages are the right tool for declarative data access in Web applications and that Xcerpt is a significant step towards a more convenient, yet highly efficient data access in a “Web of Data”
Shortest Path Trajectory System Based on Dijkstra Algorithm
In the master project, the researcher discussed the shortest path solution to a single source problem based on Dijkstra algorithm as resolving the basic concepts. Everybody can travel by different routes to reach a different destination point. This can be time consuming if they do not travel trough the best route. This project aims to determine locations of the node that reflect all the items in the list, build the route by connecting nodes and evaluate the proposed algorithm for the single source shortest path problem. This project includes the modification of main algorithm which has been implemented in the prototype development. This study discussed the emphasis on the single source shortest path at the location of specific studies. The study will produce a decision-makers prototype
Distributed Processing of k Shortest Path Queries over Dynamic Road Networks
The problem of identifying the k-shortest paths (KSPs for short) in a dynamic
road network is essential to many location-based services. Road networks are
dynamic in the sense that the weights of the edges in the corresponding graph
constantly change over time, representing evolving traffic conditions. Very
often such services have to process numerous KSP queries over large road
networks at the same time, thus there is a pressing need to identify
distributed solutions for this problem. However, most existing approaches are
designed to identify KSPs on a static graph in a sequential manner (i.e., the
(i+1)-th shortest path is generated based on the i-th shortest path),
restricting their scalability and applicability in a distributed setting. We
therefore propose KSP-DG, a distributed algorithm for identifying k-shortest
paths in a dynamic graph. It is based on partitioning the entire graph into
smaller subgraphs, and reduces the problem of determining KSPs into the
computation of partial KSPs in relevant subgraphs, which can execute in
parallel on a cluster of servers. A distributed two-level index called DTLP is
developed to facilitate the efficient identification of relevant subgraphs. A
salient feature of DTLP is that it indexes a set of virtual paths that are
insensitive to varying traffic conditions, leading to very low maintenance cost
in dynamic road networks. This is the first treatment of the problem of
processing KSP queries over dynamic road networks. Extensive experiments
conducted on real road networks confirm the superiority of our proposal over
baseline methods.Comment: A shorter version of this technical report has been accepted for
publication as a full paper in ACM SIGMOD 2020: International Conference on
Management of Dat
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