1,721,137 research outputs found
SPARQL with property paths on the Web
Full text linkLinked Data on the Web represents an immense source of knowledge suitable to be automatically processed and queried. In this respect, there are different approaches for Linked Data querying that differ on the degree of centralization adopted. On one hand, the SPARQL query language, originally defined for querying single datasets, has been enhanced with features to query federations of datasets; however, this attempt is not sufficient to cope with the distributed nature of data sources available as Linked Data. On the other hand, extensions or variations of SPARQL aim to find trade-offs between centralized and fully distributed querying. The idea is to partially move the computational load from the servers to the clients. Despite the variety and the relative merits of these approaches, as of today, there is no standard language for querying Linked Data on theWeb. A specific requirement for such a language to capture the distributed, graph-like nature of Linked Data sources on the Web is a support of graph navigation. Recently, SPARQL has been extended with a navigational feature called property paths (PPs). However, the semantics of SPARQL restricts the scope of navigation via PPs to single RDF graphs. This restriction limits the applicability of PPs for querying distributed Linked Data sources on the Web. To fill this gap, in this paper we provide formal foundations for evaluating PPs on the Web, thus contributing to the definition of a query language for Linked Data. We first introduce a family of reachability-based query semantics for PPs that distinguish between navigation on the Web and navigation at the data level. Thereafter, we consider another, alternative query semantics that couples Web graph navigation and data level navigation; we call it context-based semantics. Given these semantics, we find that for some PP-based SPARQL queries a complete evaluation on the Web is not possible. To study this phenomenon we introduce a notion of Web-safeness of queries, and prove a decidable syntactic property that enables systems to identify queries that areWeb-safe. In addition to establishing these formal foundations, we conducted an experimental comparison of the context-based semantics and a reachability- based semantics. Our experiments show that when evaluating a PP-based query under the context-based semantics one experiences a significantly smaller number of dereferencing operations, but the computed query result may contain less solutions.Funding Agencies|German Government, Federal Ministry of Education and Research [03WKCJ4D]; Cyber Security Technological District - Italian MIUR</p
A context-based semantics for SPARQL property paths over the web
No full textAs of today, there exists no standard language for querying Linked Data on the Web, where navigation across distributed data sources is a key feature. A natural candidate seems to be SPARQL, which recently has been enhanced with navigational capabilities thanks to the introduction of property paths (PPs). However, the semantics of SPARQL restricts the scope of navigation via PPs to single RDF graphs. This restriction limits the applicability of PPs on the Web. To fill this gap, in this paper we provide formal foundations for evaluating PPs on the Web, thus contributing to the definition of a query language for Linked Data. In particular, we introduce a query semantics for PPs that couples navigation at the data level with navigation on the Web graph. Given this semantics we find that for some PP-based SPARQL queries a complete evaluation on the Web is not feasible. To enable systems to identify queries that can be evaluated completely, we establish a decidable syntactic property of such queries
PROV-AQ: Provenance Access and Query
No full textThis document specifies how to use standard Web protocols, including HTTP, to obtain information about the provenance of resources on the Web. We describe both simple access mechanisms for locating provenance information associated with web pages or resources, and provenance query services for more complex deployments. This is part of the larger W3C Prov provenance framework
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
HomeRun:A Cardinality Estimation Advisor for Graph Databases
Full text linkDatabase systems depend on cardinality estimates for generation of optimal query execution plans. Selecting an appropriate cardinality estimation technique involves navigating trade-offs, including the accuracy of estimates, time required for estimation, and necessary statistics. These trade-offs can lead to different choices based on the dataset and query workload. Unfortunately there is limited support for advising graph database users in exploring these trade-offs and making the right choices for their scenarios. To address this critical gap, we introduce an advisor tool, HomeRun, which analyzes the performance of various cardinality estimation techniques in given usage scenarios. We explain HomeRun's capabilities using the industry-standard LSQB benchmark and synthetic scenarios. HomeRun reveals how minor changes in the dataset can significantly impact the conclusions about the performance of cardinality estimation techniques.</p
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Knowledge Discovery for Provenance Research on Colonial Heritage Objects
No full textHeritage institutions hold rich information on cultural heritage objects involving contextual information about people, places, times, and events. This information is usually kept in institutional silos, where domain researchers often work with data across institutions. Linking entities among different institutions can enrich these data sources and, in turn, aid domain research. The aggregated version of data can be further used to infer insightful knowledge that can excel in one of the time-consuming tasks of the domain, which is provenance research. This research will first focus on entity linking across institutions to construct a Knowledge Graph representing both structured metadata of objects and the collector's biography. This work aims to use this newly formed Knowledge Graph to find interesting patterns to scale-up provenance research and analyse the effect of adding such information to the current data source. Experiments with the different modalities of data and pattern mining techniques will reveal to which extent this data enrichment places a role in finding useful knowledge for the heritage objects' provenance research.</p
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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