Search results for "SPARQL"
showing 10 items of 42 documents
Export of Relational Databases to RDF Databases: A Case Study
2010
The vast amount of business information nowadays is stored in relational databases. For the Semantic Web vision to become a reality, we need ways how to exploit this data in form of RDF triples. The universal and commonly accepted solution for this problem still does not exist. In most cases, mapping languages are used for specification of correspondences between OWL ontology and DB schema. At the same time, these languages generally are not well suited for specification of mappings in cases when there is a substantial difference between OWL ontology and DB schema. In this paper, we describe a new model transformation-based method for specification of correspondences between the elements of…
Faceted Search Over RDF-Based Knowledge Graphs
2016
Knowledge graphs such as Yago and Freebase have become a powerful asset for enhancing search, and are being intensively used in both academia and industry. Many existing knowledge graphs are either available as Linked Open Data, or they can be exported as RDF datasets enhanced with background knowledge in the form of an OWL 2 ontology. Faceted search is the de facto approach for exploratory search in many online applications, and has been recently proposed as a suitable paradigm for querying RDF repositories. In this paper, we provide rigorous theoretical underpinnings for faceted search in the context of RDFbased knowledge graphs enhanced with OWL 2 ontologies. We identify well-defined fra…
A framework for context-sensitive metadata description
2006
Expectations regarding the new generation of Web depend on the success of Semantic Web technology. Resource Description Framework (RDF) is a basis for explicit and machine-readable representation of semantics. However RDF is not suitable for describing dynamic and context-sensitive resources (eg. processes). We present the Context Description Framework (CDF) as an extension of the RDF by adding a 'TrueInContext' component to the basic RDF triple ('subject-predicate-object'), and consider contextual value as a container of RDF statements. We also add a probabilistic component, which allows multilevel contextual dependence descriptions as well as presumes possibility for Bayesian reasoning wi…
ViziQuer: A Tool to Explore and Query SPARQL Endpoints
2011
The presented tool uses a novel approach to explore and query a SPARQL endpoint. The tool is simple to use as a user needs only to enter an address of a SPARQL endpoint of one's interest. The tool will extract and visualize graphically the data schema of the endpoint. The user will be able to overview the data schema and use it to construct a SPARQL query according to the data schema. The tool can be downloaded from http://viziquer.lumii.lv. There is also additional information and help on how to use it in practice.
Export of Relational Databases to RDF Databases by Model Transformations
2011
The Semantic Web is a Web of Data. To fulfill this web with data we need methods how to transfer business data from existing relational databases. In most cases, textual mapping languages are used for the specification of correspondences between relational DB schema and OWL ontology. These languages generally are rather awkward and not well-suited for the specification of mappings in cases when there is a substantial semantic gap between the source ER schema and the target OWL ontology. At the same time specification of mappings is a classical use case for graphical model transformation languages. In our previous work [10] we have proposed a new, model transformation-based method for the sp…
Ontology-based cooperation of information systems : contributions to database-to-ontology mapping and XML-to-ontology mapping
2010
This thesis treats the area of ontology-based cooperation of information systems. We propose a global architecture called OWSCIS that is based on ontologies and web-services for the cooperation of distributed heterogeneous information systems. In this thesis, we focus on the problem of connecting the local information sources to the local ontologies within OWSCIS architecture. This problem is articulated by three main axes: 1) the creation of the local ontology from the local information sources, 2) the mapping of local information sources to an existing local ontology, and 3) the translation of queries over the local ontologies into queries over local information sources.
Vizuāli semantiski vaicājumi pār relāciju datubāzēm
2020
Korektu vaicājumu izveide ir svarīgākais posms datu izguves procesā. Konstruējot vaicājumu vizuāli, tiek sniegta iespēja iegūt korektus datus ne tikai jomas speciālistiem, bet arī citu profesiju pārstāvjiem bez specifiskām tekstuālās vaicājuma valodas sintakses zināšanām. Dažādas vaicājumu bāzētas valodas kā SPARQL tiek izmantotas, lai iegūtu datus no semantiskā tīmekļa, bet, izmantojot minēto vaicājumu valodu, nav iespējams tieši izgūt datus no relāciju datubāzēm. Ontoloģijā bāzēta datu piekļuve ir kļuvusi par populāru pieeju lielo datu laikmetā. Darbā tiek apskatīta iespēja OBDA pieejas ietvaros veikt vizuāli semantisku vaicājumu izpildi, pār relāciju datubāzēm izmantojot R2RML. Izmantojo…
Schema-Backed Visual Queries over Europeana and Other Linked Data Resources
2021
We describe and demonstrate the process of extracting a data-driven schema of the Europeana cultural heritage Linked data resource (with actual data classes, properties and their connections, and cardinalities) and application of the extracted schema to create a visual query environment over Europeana. The extracted schema information allows generating SHACL data shapes describing the actual data endpoint structure. The schema extraction process can be applied also to other data endpoints with a moderate data schema size and a potentially large data triple count, as e.g., British National Bibliography Linked data resource.
ViziQuer: A Web-Based Tool for Visual Diagrammatic Queries Over RDF Data
2018
We demonstrate the open source ViziQuer tool for web-based creation and execution of visual diagrammatic queries over RDF/SPARQL data. The tool supports the data instance level and statistics queries, providing visual counterparts for most of SPARQL 1.1 select query constructs, including aggregation and subqueries. A query environment can be created over a user-supplied SPARQL endpoint with known data schema (a data schema exploration service is available, as well). There are pre-defined demonstration query environments for a mini-university data set, a fragment of synthetic similar to reality hospital data set, and a variant of Linked Movie Database RDF data set.
Integration of Spatial processing and knowledge Processing through the Semantic Web Stack
2011
International audience; This paper presents the integration process of spatial technologies and Semantic Web technologies and its associated tool. The result of this work is a spatial query and rule engine of spatial. To do so, existing ontology with spatial elements is adjusted in order to process the spatial knowledge through spatial technologies. This paper outlines the methods and the processes of these adjustments and how results are returned by our tool. The SWRL and the SPARQL language are extended for spatial purpose and the existing OWL ontology wine is used as an application example.