SPARQL Update query¤

The SPARQL UPDATE query plugin is a task for outputting SPARQL UPDATE queries from the input RDF data source.

Description¤

The SPARQL Update query plugin is an example of a task. Notice well that this plugin is neither a RDF task nor a RDF dataset. This is in contrast to e.g. the SPARQL Select query and the SPARQL endpoint, respectively.

More specifically, this means the following: This plugin does not execute SPARQL queries of any sort, but generates them. It generates SPARQL Update queries from a templating engine. In order to execute these queries, we need to connect this task from an input into an output RDF dataset.

Templating¤

The SPARQL Update query plugin uses a template in order to construct and output SPARQL update queries. There are two possible template engines supported by this plugin: a Simple engine and Velocity Engine. Each of these engines supports a different set of templating features, such as for example variable interpolation with the dollar sign ($), i.e. filling in input values via placeholders in the template.

Example of the `Simple` mode¤

  DELETE DATA { ${<PROP_FROM_ENTITY_SCHEMA1>} rdf:label ${"PROP_FROM_ENTITY_SCHEMA2"} }
  INSERT DATA { ${<PROP_FROM_ENTITY_SCHEMA1>} rdf:label ${"PROP_FROM_ENTITY_SCHEMA3"} }

This will insert the URI serialization of the property value PROP_FROM_ENTITY_SCHEMA1 for the ${<PROP_FROM_ENTITY_SCHEMA1>} expression. Furthermore, it will insert a plain literal serialization for the property values PROP_FROM_ENTITY_SCHEMA2 and PROP_FROM_ENTITY_SCHEMA3 for the template literal expressions.

It is also possible to write something like ${"PROP"}^^<http://someDatatype> or ${"PROP"}@en. In other words, we can combine variable substitutions with fixed expressions to construct semi-flexible expressions within the template.

Example of the `Velocity Engine` mode¤

  DELETE DATA { $row.uri("PROP_FROM_ENTITY_SCHEMA1") rdf:label $row.plainLiteral("PROP_FROM_ENTITY_SCHEMA2") }
  #if ( $row.exists("PROP_FROM_ENTITY_SCHEMA1") )
    INSERT DATA { $row.uri("PROP_FROM_ENTITY_SCHEMA1") rdf:label $row.plainLiteral("PROP_FROM_ENTITY_SCHEMA3") }
  #end

Input values are accessible via various methods of the row variable (used with $row):

$row.uri(inputPath: String): Renders an input value as URI. Throws an exception if the value isn’t a valid URI.
$row.plainLiteral(inputPath: String): Renders an input value as plain literal, i.e. it escapes problematic characters, etc.
$row.rawUnsafe(inputPath: String): Renders an input value as is, i.e. no escaping is done. This should only be used if the input values can be trusted.
$row.exists(inputPath: String): Returns true if a value for the input path exists, else false.

The methods uri, plainLiteral and rawUnsafe throw an exception if no input value is available for the given input path.

In addition to input values, properties of the input and output tasks can be accessed via the inputProperties and outputProperties objects. The available keys in these objects are dynamic and correspond exactly to the configuration parameters of the tasks connected to the input and output ports of this operator.

To find the available keys for $inputProperties, check the parameter names of the task connected to the input port.
To find the available keys for $outputProperties, check the parameter names of the task connected to the output port.

For example, if the connected input task has a parameter named graph, you can access it as $inputProperties.uri("graph"). Similarly, if the connected output task has a parameter named endpoint, you can access it as $outputProperties.uri("endpoint").

Both inputProperties and outputProperties support the same methods as the row object:

uri(inputPath: String)
plainLiteral(inputPath: String)
rawUnsafe(inputPath: String)
exists(inputPath: String)

For more information about the Velocity Engine, visit http://velocity.apache.org.

Internal Specifics¤

In contrast to the SPARQL select operator, no FROM clause gets injected into the query.

Parameter¤