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Configuration-SPARQL-Datasets.md

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Configuring SPARQL Datasets

SPARQL Datasets are an abstraction dotNetRDF which separates the Leviathan engine (our in-memory SPARQL engine) from the data so that arbitrary datasets can be plugged into it. This allows for datasets which don't have to be in-memory themselves though they do have to materialise triples in-memory as needed by the engine.

As a general rule anywhere you could have used a Triple Store (see Configuration API - Triple Stores) via the dnr:usingStore property you can use a Dataset instead via the dnr:usingDataset property.

Datasets are configured using the Configuration Vocabulary in a number of ways, as each dataset is different each has its own unique configuration.

In-Memory Datasets

The in-memory dataset represents pure in-memory data which is the default operation mode for Leviathan. Any IInMemoryQueryableStore instance can be wrapped in a InMemoryDataset.

The following example shows a Triple Store configuration being specified as the underlying source for a Dataset configuration:

@prefix dnr: <http://www.dotnetrdf.org/configuration#> .

_:dataset a dnr:SparqlDataset ;
  dnr:type "VDS.RDF.Query.Datasets.InMemoryDataset" ;
  dnr:usingStore _:store .

_:store a dnr:TripleStore ;
  dnr:type "VDS.RDF.TripleStore" ;
  dnr:usingGraph _:a ;
  dnr:usingGraph _:b .

_:a a dnr:Graph ;
  dnr:type "VDS.RDF.Graph" ;
  dnr:fromFile "example.rdf" .

_:b a dnr:Graph ;
  dnr:type "VDS.RDF.Graph" ;
  dnr:fromUri <http://dbpedia.org/resource/Southampton> .

As you can see for an in-memory dataset you simply connect it to a dnr:TripleStore definition using the dnr:usingStore property.

You may alternatively use the InMemoryQuadDataset just by changing the value of the dnr:type property appropriately. The quad dataset may be more performant if your queries access named graphs frequently.

Web Demand Datasets

The WebDemandDataset is a wrapper around another dataset that allows the dataset to load missing graphs on demand from the web. It can be configured simply like so:

@prefix dnr: <http://www.dotnetrdf.org/configuration#> .

_:dataset a dnr:SparqlDataset ;
  dnr:type "VDS.RDF.Query.Datasets.WebDemandDatset" ;
  dnr:usingDataset _:memDataset .

_:memDataset a dnr:SparqlDataset ;
  dnr:type "VDS.RDF.Query.Datasets.InMemoryQuadDataset" .