Gabriela Montoya

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A large number of SPARQL endpoints are available to access the Linked Open Data cloud, but query capabilities still remain very limited. Thus, to support efficient semantic data management of federations of endpoints, existing SPARQL query engines require to be equipped with new functionalities. First, queries need to be decomposed into sub-queries not only(More)
Testbeds proposed so far to evaluate, compare, and eventually improve SPARQL query federation systems have still some limitations. Some variables and configurations that may have an impact on the behavior of these systems (e.g., network latency, data partitioning and query properties) are not sufficiently defined; this affects the results and repeatability(More)
Federated query engines allow to consume linked data from SPARQL endpoints. Replicating data fragments from different sources allows to re-organize data to better fit federated query processing of data consumers. However, existing federated query engines poorly support replication. In this paper, we propose a replication-aware federated query engine that(More)
We present DEFENDER and illustrate the benefits of identifying promising query decompositions and efficient plans that combine results from federations of SPARQL endpoints. DEFENDER is a query decomposer that implements a two-fold approach. First triple patterns in a SPARQL query are decomposed into simple sub-queries that can be completely executed on one(More)
The Local-As-View (LAV) integration approach aims at querying heterogeneous data in dynamic environments. In LAV, data sources are described as views over a global schema which is used to pose queries. Query processing requires to generate and execute query rewritings, but for SPARQL queries, the LAV query rewritings may not be generated or executed in a(More)
Local-As-View (LAV) mediators provide a uniform interface to a federation of heterogeneous data sources to attempt the execution of queries against the federation. LAV mediators rely on query rewriters to translate mediator queries into equivalent queries on the federated data sources. The query rewriting problem in LAV mediators has shown to be(More)
Data replication and deployment of local SPARQL endpoints improve scalability and availability of public SPARQL endpoints, making the consumption of Linked Data a reality. This solution requires synchronization and specific query processing strategies to take advantage of replication. However, existing replication aware techniques in federations of SPARQL(More)
SemLAV allows to execute SPARQL queries against the Deep Web and Linked Open Data data sources. It implements the mediatorwrapper architecture based on view definitions over remote data sources. SPARQL queries are expressed using a mediator schema vocabulary, and SemLAV selects relevant data sources and rank them. The ranking strategy is designed to deliver(More)