Browsing by Author "Soto, Adrian"

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    Querying APIs with SPARQL
    (2022) Mosser, Matthieu; Pieressa, Fernando; Reutter, Juan L.; Soto, Adrian; Vrgoc, Domagoj
    Although the amount of RDF data has been steadily increasing over the years, the majority of information on the Web is still residing in other formats, and is often not accessible to Semantic Web services. A lot of this data is available through APIs serving JSON documents. In this work we propose a way of extending SPARQL with the option to consume JSON APIs and integrate this information into SPARQL query answers, obtaining a language that combines data from the "traditional" Web to the Semantic Web. Our proposal is based on an extension of the SERVICE operator with the ability to connect to JSON APIs. With the aim of evaluating these queries as efficiently as possible, we show that the main bottleneck is the amount of API requests, and present an algorithm that produces "worst-case optimal" query plans that reduce the number of requests as much as possible. We note that the analysis of this algorithm is studied in terms of an algorithm for evaluating relational queries with access methods with the minimal number of access queries, which is of independent interest. We show the superiority of the worst-case optimal approach in a series of experiments that take existing SPARQL benchmarks, and augment them with the ability to connect to JSON APIs in order to obtain additional information. (C) 2020 Elsevier Ltd. All rights reserved.
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    Recursion in SPARQL
    (2021) Reutter, Juan L.; Soto, Adrian; Vrgoc, Domagoj
    The need for recursive queries in the Semantic Web setting is becoming more and more apparent with the emergence of datasets where different pieces of information are connected by complicated patterns. This was acknowledged by the W3C committee by the inclusion of property paths in the SPARQL standard. However, as more data becomes available, it is becoming clear that property paths alone are not enough to capture all recursive queries that the users are interested in, and the literature has already proposed several extensions to allow searching for more complex patterns.