# Comunica SPARQL Service RDF Metadata Extract Actor

[![npm version](https://badge.fury.io/js/%40comunica%2Factor-rdf-metadata-extract-sparql-service.svg)](https://www.npmjs.com/package/@comunica/actor-rdf-metadata-extract-sparql-service)

An [RDF Metadata Extract](https://github.com/comunica/comunica/tree/master/packages/bus-rdf-metadata-extract) actor that
extracts [SPARQL Service Description metadata](https://www.w3.org/TR/sparql11-service-description/).

This module is part of the [Comunica framework](https://github.com/comunica/comunica),
and should only be used by [developers that want to build their own query engine](https://comunica.dev/docs/modify/).

[Click here if you just want to query with Comunica](https://comunica.dev/docs/query/).

## Install

```bash
$ yarn add @comunica/actor-rdf-metadata-extract-sparql-service
```

## Metadata entries

This actor adds the following entries to the metadata object.

* `sparqlService`: Value of `http://www.w3.org/ns/sparql-service-description#endpoint`.
* `defaultGraph`: Value of `http://www.w3.org/ns/sparql-service-description#defaultGraph`.
* `defaultDataset`: Value of `http://www.w3.org/ns/sparql-service-description#defaultDataset`.
* `unionDefaultGraph`: Boolean flag set when the service declares `http://www.w3.org/ns/sparql-service-description#UnionDefaultGraph` feature.
* `basicFederatedQuery`: Boolean flag set when the service declares `http://www.w3.org/ns/sparql-service-description#BasicFederatedQuery` feature.
* `inputFormats`: List of `http://www.w3.org/ns/sparql-service-description#inputFormat` when available.
* `resultFormats`: List of `http://www.w3.org/ns/sparql-service-description#resultFormat` when available.
* `supportedLanguages`: List of `http://www.w3.org/ns/sparql-service-description#supportedLanguage` when available.

## Configure

After installing, this package can be added to your engine's configuration as follows:
```json
{
  "@context": [
    "https://linkedsoftwaredependencies.org/bundles/npm/@comunica/actor-rdf-metadata-extract-sparql-service/^4.0.0/components/context.jsonld"
  ],
  "actors": [
    {
      "@id": "urn:comunica:default:rdf-metadata-extract/actors#sparql-service",
      "@type": "ActorRdfMetadataExtractSparqlService"
    }
  ]
}
```

### Config Parameters

* `inferHttpsEndpoint`: If HTTPS endpoints should be forcefully used if the original URL was HTTPS-based, defaults to `true`.