In this document, we show how to build custom connectors to any NLP / text analytics library to perform text analytics tasks. These connectors handle the invocation of the underlying library to process text data in table columns, in the query processing pipeline.

The component Sclera - Apache OpenNLP Connector is built using this SDK. For examples of how the connector is used in Sclera, please refer to the documentation on using text analytics in SQL.

Building Text Analytics Library Connectors

To build a custom datasource connector, you need to provide implementations of the following abstract classes in the SDK:

  • NlpService (Scala, Java)
    • Provides text analytics operators as a service to Sclera, using the specified library.
    • Contains an id that identifies this service.
    • Contains the method createObject that is used to create a new task object for the task named in the parameter taskName for this service.
  • NlpTask (Scala, Java)
    • Wrapper over classes implementing text analytics algorithms.
    • Provides a function eval that takes a data stream (an iterator over rows, with associated metadata) as input and returns the same data stream, with each row augmented by columns resultCols containing the output of executing the task taskName on the text in column inputCol. If the evaluation on a row emits multiple evaluation results, the input row is repeated in the output for each such result.

The Sclera - Apache OpenNLP Connector, included with the Sclera platform, is open source and implements the interface mentioned above. The code for the Sclera - Apache OpenNLP Connector, in Scala, also appears as an illustrative example in the Sclera Extensions (Scala) Github repository.

Packaging and Deploying the Connector

The included Sclera - Apache OpenNLP Connector implementation uses sbt for building the connector (installation details). This is not a requirement – any other build tool can be used instead.


For Scala:

  • The Scala implementation has a dependency on the "sclera-core" library. This library is available from the Sclera repository; see the included sbt build file for the details. Note that the dependency is annotated "provided" since the jar for "sclera-core" will be available in the CLASSPATH when this connector is run with Sclera.

For Java:

Deployment Steps

The connector can be deployed using the following steps:

Alternative 1 (Recommended)

  • First, publish the implementation as a local package. In sbt, this is done by running sbt publish-local.
  • Run the following to install the component and its dependencies:

    > $SCLERA_HOME/bin/ package_name package_version package_org
    • $SCLERA_HOME is the directory where Sclera is installed
    • package_name is the name of the package being installed
    • package_version is the version of the package being installed
    • package_org is the org of the package being installed
  • Run the following to include the path to the installed component package jar and the dependencies in the CLASSPATH:

    > . $SCLERA_HOME/assets/install/classpath/
    • The bash script was automatically created in the previous step, while installing the package. The package_name part of the file name is the name of the package installed.

The connector should now be visible to Sclera, and can be used in the queries.

Alternative 2

  • First, compile and package the implementation into a jar file. In sbt, this is done by running sbt package. If you have external dependencies, you may need to assemble everything into a single jar – in sbt, this can be done using the sbt-assembly plugin.
  • Next, add the path to the generated jar file to the CLASSPATH environment variable.

The connector should now be visible to Sclera, and can be used in the queries.

Note: Please ensure that the identifier you assign to the connector is unique, that is - does not conflict with the identifier of any other available NlpService instance.

Related Documentation