CODEWITHSUNDEEP
sparqlsemantic-weblinked-data
Wisamx
Wisamx

Reputation: 303

Is there a central SPARQL endpoint for the semantic web

We are going to have the semantic web. Now we have LOD cloud.

Every data set has its own SPARQL endpoint.

I can query the dataset triples.

How can I query the whole semantic web or LOD?

Upvotes: 0

Views: 348

Answers (5)

Andre Valdestilhas
Andre Valdestilhas

Reputation: 15

It's still a prototype, which means bugs, but one of the aims of wimuQ is to provide a way to query all 539 public SPARQL endpoints + all datasets from LODLaundromat and LODStats, that is more than 600,000 datasets, more than 5 terabytes. As far as I know, it is the most extensive collection datasets accessible from one single place.

For more information, the paper is available here:

Upvotes: 0

Kingsley Uyi Idehen
Kingsley Uyi Idehen

Reputation: 925

There is no central point regarding the notion of a Semantic Web of Linked Data. Instead, like any Super Information Highway, you have major concentration points (hubs or junctions) that enable you to discover routes to a variety of destinations.

Major Semantic Web of Linked Data hubs that we oversee at OpenLink Software include:

  1. DBpedia
  2. DBpedia-Live
  3. URIBurner
  4. LOD Cloud Cache

Remember, the fundamental principle behind Linked Open Data is that hyperlinks (HTTP URIs) function as words in sentences constructed using RDF Language. Thus, you can use the SPARQL Query Language to produce query solutions (tables or graphs) that expose desired routes (e.g., using Property Paths).

Finally, you can also use Federated SPARQL Query (SPARQL-FED) to navigate a Semantic Web of Linked Data.

Examples:

select distinct * 
where { 
        ?s a <http://dbpedia.org/ontology/AcademicJournal> ; 
        rdf:type{1,3} ?o 
       } 

LIMIT 50

Query Solution Document Link.

We are also working on a publicly available Google Spreadsheet that provides additional information related to the kinds of datasets accessible via the LOD Cloud that we maintain.

Upvotes: 2

szymon
szymon

Reputation: 327

To my knowledge LOD-a-lot is currently the one ongoing effort that gets closest to the vision of querying the whole web of data. And this is obviously done using different means than SPARQL endpoints.

Upvotes: 1

knb
knb

Reputation: 9295

There exists a W3C-owned and (un-?)maintained wiki page with ~60 SPARQL endpoints. Many "last accessed/checked" entries are from 2010. On that page is a link to http://sparqles.ai.wu.ac.at/availability which lists more endpoints and is much more recent and up-to-date.

Read the 2nd paragraphs titled "SPARQL Endpoints" of the blogpost Querying DBpedia with GraphQL for a skeptical view of the state of SPARQL today. Cannot say it any better myself.

Also note that SPARQL permits every endpoint to offer any number of "named GRAPH" constructs that can be queried at that endpoint. So that is another feature more to consider.

Upvotes: 5

Leslie Sikos
Leslie Sikos

Reputation: 549

No, there is no such single SPARQL endpoint, because the Semantic Web is decentralized by design. However, SPARQL 1.1 supports federated queries over different SPARQL endpoints using the SERVICE keyword. See https://www.w3.org/TR/sparql11-federated-query/ for reference. More specifically, there is a mention in the literature about how to determine which data sources might be relevant for query answering at Internet scale:

Hartig O., Bizer C., Freytag J.C. (2009) Executing SPARQL queries over the Web of Linked Data. In: Bernstein A. et al. (eds.) The Semantic Web – ISWC 2009. ISWC 2009. Lecture Notes in Computer Science, vol. 5823, pp. 293–309. Heidelberg: Springer. doi: 10.1007/978-3-642-04930-9_19

Upvotes: 6

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