What is a Virtuoso SPARQL Endpoint, and why is it important?

A Virtuoso SPARQL Endpoint is a feature of every Virtuoso RDBMS instance that offers an HTTP-based Query Service that operates on Entity Relationship Types (Relations) represented as RDF sentence collections using the SPARQL Query Language. These operations may be read- and/or write-oriented and distributed without compromising security, performance, or scalability.

Typical Virtuoso Default SPARQL Endpoint exposed as an HTML-based Query Editor

SPARQL Grey Areas and Challenges

Despite the awesome power delivered by the SPARQL Query Language — a W3C open standard for declarative interaction with Entity Relationship Types (Relations) represented as subject→predicate→object structured sentence graphs (courtesy of the the RDF open standard) — there are some important grey areas that are somewhat underspecified or a little unclear with regard to a Semantic Web of Linked Data. Examples include —

  • Lookups (de-references) of Constants — How is follow-your-nose exploration (de-reference and load) handled as part of a query processing pipeline, especially regarding HTTP URI-constants (e.g., <http://dbpedia.org>) that identify Named Graphs (Data Source Names) and/or Subjects, Predicates, and Objects of Relations expressed in the body of a query?
  • Lookups (de-references) of Variables — How is Linked Data’s follow-your-nose exploration (de-reference and load) handled as part of a query processing pipeline, especially regarding SPARQL variables (such as ?s or ?name) that resolve to HTTP URIs which then identify Named Graphs (Data Source Names) and/or Subjects, Predicates, and Objects of Relations expressed in the body of a query?
  • Lookup (de-reference) Properties and/or Property Paths identified by Variables — What predicates (e.g., rdfs:seeAlso, foaf:knows, other predicates of this nature) within a Semantic Web of Linked Data should be crawled?
  • Lookup (de-reference) Depths for Properties and/or Property Paths identified by Variables — Having identified some predicate(s) to crawl, how far should the crawl extend?
  • Implications for Reasoning and Inference — When crawling a Semantic Web of Linked Data, when should — or shouldn’t — Reasoning and Inference be invoked?
  • Implications of the World Wide Web — How are all of these handled at Web-scale, i.e., via SPARQL Query Service endpoints (including those that may not support the basic SPARQL Protocol and/or Federated SPARQL [a/k/a SPARQL-FED])?
  • Implications for Query Complexity — How are expensive queries along dataset size or solution production time axis handled?

Virtuoso SPARQL Endpoint

Virtuoso’s SPARQL implementation handles these important and challenging issues as part of its unique ability to make distributed queries at Web-scale both feasible and demonstrable — as reflected by its pivotal role in the massive Linked Open Data (LOD) Cloud anchored by DBpedia (one of many public Virtuoso instances).

Virtuoso’s built-in SPARQL Query Service functionality delivers a variety of capabilities:

  • Supports the HTTP-based SPARQL Query Service Protocol
  • Supports Federated SPARQL (a/k/a SPARQL-FED) — inclusion of a SERVICE clause that identifies an external SPARQL Protocol endpoint upon which to execute a sub-query — as one option for executing federated queries over SPARQL endpoints from the LOD Cloud
  • Supports optional de-referencing of variables and constants in the body of a query, thereby incorporating content crawling over external data sources into the query solution production pipeline
  • Leverages “Anytime Query” functionality that ensures some (possibly incomplete) solution is provided to any querent (human or machine), irrespective of query complexity or data volume associated with solution
  • Delivers Business Intelligence and Analytics functionality via SPARQL-BI extensions, meeting the needs of sophisticated analytics oriented reports, e.g., TPC-H and various types of Graph Analytics query
  • Supports a wide variety of query solution document types including (among others) HTML, CSV, JSON, and XML for SELECT Queries, and RDF-Turtle, RDF-N-Triples, JSON-LD, and RDF-XML for DESCRIBE and CONSTRUCT Queries
  • Adds Extract, Transform, and Load operations to the query solution production pipeline through built-in integration with Virtuoso RDF Transformation Middleware (or RDFizer), commonly referred to as the Sponger — which also includes cache invalidation functionality
  • Supports HTTP Content Negotiation ("conneg"), both Basic and Dynamic via QoS algorithms
  • Provides unrivaled performance and scale — from Small Data to Big Data (be it Decision Support or OLTP usage patterns)
  • Provides unrivaled Data Security, courtesy of Attribute-Based Access Controls (ABAC)
  • Also exploitable by ODBC, JDBC, ADO.NET, OLE DB, and XMLA applications as an open standards-based extension to SQL

Conclusion

A Virtuoso SPARQL endpoint is a major feature of every Virtuoso instance that delivers on the promise of increased expressivity and data access dexterity required by Knowledge Graphs that manifest as an AI-friendly Semantic Web of Linked Data. Fundamentally, it is an indispensable tool for modern data access, management, and integration.

Related

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Kingsley Uyi Idehen

Written by

Founder & CEO, OpenLink Software — provider of Secure, High-Performance, and Cross-Platform Data Access, Integration, Virtualization, and Management Technology.

OpenLink Virtuoso Weblog

News & Articles related to OpenLink Virtuoso & Related Technologies

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