The Query class is used to execute a query on a Model object using the default query language SPARQL. For more information, please refer to https://librdf.org/rasqal/ for details on supported query languages.
Details
A Query is executed using the executeQuery method, which returns a QueryResults object that can be iterated over the query solution sequence.
Methods
Query-initialize: Initialize a Query object.executeQuery: Execute a query.setQueryResultLimit: Set limit on returned query results.getQueryResultLimit: Get the query result limit.getResults: Return all query results.writeResults: Write query results to a file.freeParser: Free memory used by a librdf query.
See also
redland: redland package
Examples
world <- new("World")
storage <- new("Storage", world, "hashes", name="", options="hash-type='memory'")
model <- new("Model", world, storage, options="")
stmt <- new("Statement", world=world,
subject="https://cn.dataone.org/cn/v1/resolve/urn:uuid:274a0c5c-3082-4562-bbd3-2b1288768cac",
predicate="http://www.w3.org/ns/prov#hadPlan",
object="https://cn.dataone.org/cn/v1/resolve/urn:uuid:01305f45-f22b-40c8-8d27-00357d01e4a5")
status <- addStatement(model, stmt)
stmt <- new("Statement", world=world,
subject="https://orcid.org/0000-0002-2192-403X",
predicate="http://www.w3.org/ns/prov#Agent",
object="slaughter",
objectType="literal",
datatype_uri="http://www.w3.org/2001/XMLSchema#string")
status <- addStatement(model, stmt)
queryString <-
paste("PREFIX orcid: <https://orcid.org/>",
"PREFIX dataone: <https://cn.dataone.org/cn/v1/resolve/>",
"PREFIX prov: <http://www.w3.org/ns/prov#>",
"SELECT ?a ?c WHERE { ?a prov:Agent ?c . }", sep=" ")
query <- new("Query", world, queryString, base_uri=NULL, query_language="sparql", query_uri=NULL)
# Return all results as a string
results <- getResults(query, model, "rdfxml")