# RDF String Turtle

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This package contains utility functions to convert between the string-based
and [RDFJS](https://github.com/rdfjs/representation-task-force/) representations of RDF terms, quads and triples.

_This is a fork of [RDF String](https://github.com/rubensworks/rdf-string.js) that is adapted to make string representation compatible with Turtle/SPARQL syntax._

This allows for convenient and compact interaction with RDF terms and quads,
as they can be serialized as plain JSON.

Quads are represented as follows:
```
{
  subject:   '<http://example.org/cartoons#Tom>',
  predicate: '<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>',
  object:    '<http://example.org/cartoons#Cat>'
  graph:     '<http://example.org/myGraph>'
}
```
Different terms types in quads are represented as follows:
* **URLs, URIs and IRIs are strings wrapper in `<>``**: `'<http://example.org/cartoons#Tom>'`
* **Literals are represented as double quoted strings**: `'"Tom"'`, `'"Tom"@en-gb'`, `'"Tom"@en-gb--ltr'`, `'"1"^^<http://www.w3.org/2001/XMLSchema#integer>'`
* **Blank nodes are prefixed by `_:`**: `'_:blankNodeName'`
* **Variables are prefixed by `?`**: `'?variableName'`

## Usage

The following examples assume the following imports:
```javascript
import * as RdfDataModel from "rdf-data-model";
import * as RdfString from "rdf-string-ttl";
```

### Term to string

Convert an RDFJS term to the string-based representation.

```javascript
// Prints <http://example.org>
console.log(RdfString.termToString(RdfDataModel.namedNode('http://example.org')));

// Prints _:b1
console.log(RdfString.termToString(RdfDataModel.blankNode('b1')));

// Prints "abc"
console.log(RdfString.termToString(RdfDataModel.literal('abc')));

// Prints "abc"@en-us
console.log(RdfString.termToString(RdfDataModel.literal('abc', 'en-us')));

// Prints "abc"@en-us--ltr
console.log(RdfString.termToString(RdfDataModel.literal('abc', { language: 'en-us', direction: 'ltr' })));

// Prints "abc"^^<http://example.org/>
console.log(RdfString.termToString(RdfDataModel.literal('abc', namedNode('http://example.org/'))));

// Prints ?v1
console.log(RdfString.termToString(RdfDataModel.variable('v1')));

// Prints empty string
console.log(RdfString.termToString(RdfDataModel.defaultGraph()));
```

### String to term

Convert an string-based term to the RDFJS representation.

_Optionally, a custom RDFJS DataFactory can be provided as second argument to create terms instead of the built-in DataFactory._

```javascript
// Outputs a named node
RdfString.stringToTerm('<http://example.org>');

// Outputs a blank node
RdfString.stringToTerm('_:b1');

// Outputs a literal
RdfString.stringToTerm('"abc"');

// Outputs a literal with a language tag
RdfString.stringToTerm('"abc"@en-us');

// Outputs a literal with a language tag and direction
RdfString.stringToTerm('"abc"@en-us--ltr');

// Outputs a literal with a datatype
RdfString.stringToTerm('"abc"^^<http://example.org/>');

// Outputs a variable
RdfString.stringToTerm('?v1');

// Outputs a default graph
RdfString.stringToTerm('');
```

### Quad to string-based quad

Convert an RDFJS quad to a string-based quad.

```javascript
// Prints { subject: '<http://example.org>', predicate: '<http://example.org>', object: '"abc"', graph: '' }
console.log(RdfString.quadToStringQuad(RdfDataModel.triple(
  namedNode('http://example.org'),
  namedNode('http://example.org'),
  literal('abc'),
)));
```

### String-based quad to quad

Converts a string-based quad to an RDFJS quad.

_Optionally, a custom RDFJS DataFactory can be provided as second argument to create quads and terms instead of the built-in DataFactory._

```javascript
// Outputs a quad
RdfString.stringQuadToQuad({
  subject: '<http://example.org>',
  predicate: '<http://example.org>',
  object: '"abc"',
  graph: '',
});
```

## License
This software is written by [Ruben Taelman](http://rubensworks.net/).
These utility functions are inspired by the implementation of [N3.js](https://github.com/RubenVerborgh/N3.js).

This code is released under the [MIT license](http://opensource.org/licenses/MIT).