LDflex

LDflex makes Linked Data in JavaScript fun

LDflex is a domain-specific language for querying Linked Data on the Web as if you were browsing a local JavaScript graph.

You can write things like person.friends.firstName to get a list of your friends. Thanks to the power of JSON-LD contexts and JavaScript’s Proxy, these properties are not hard-coded in LDflex, but can be chosen at runtime. They feel as if you’re traversing a local object, while you’re actually querying the Web—without pulling in all data first.

Tim Berners-Lee came up with the idea for such a fluid JavaScript interface to Linked Data, in a discussion on how to make Linked Data easier for developers.

Articles and tutorials

• Tutorial slides and walkthrough
• Cheatsheet
• Designing a Linked Data developer experience, discussing the design of LDflex
• Solid Chess, an app built with LDflex

Installation

npm install ldflex

In order to execute queries, you will also need a query engine:

npm install @ldflex/comunica

Usage

When you have obtained a starting subject, you can navigate through its properties using standard JavaScript dot property syntax.

In order to query for the result, use await if you want a single value, or for await to iterate over all values.

Initialization

const { PathFactory } = require('ldflex');
const { default: ComunicaEngine } = require('@ldflex/comunica');
const { namedNode } = require('@rdfjs/data-model');

// The JSON-LD context for resolving properties
const context = {
  "@context": {
    "@vocab": "http://xmlns.com/foaf/0.1/",
    "friends": "knows",
    "label": "http://www.w3.org/2000/01/rdf-schema#label",
    "rbn": "https://ruben.verborgh.org/profile/#"
  }
};
// The query engine and its source
const queryEngine = new ComunicaEngine('https://ruben.verborgh.org/profile/');
// The object that can create new paths
const path = new PathFactory({ context, queryEngine });

Looking up data on the Web

const ruben = path.create({ subject: namedNode('https://ruben.verborgh.org/profile/#me') });
showPerson(ruben);

async function showPerson(person) {
  console.log(`This person is ${await person.name}`);

  console.log(`${await person.givenName} is interested in:`);
  for await (const name of person.interest.label)
    console.log(`- ${name}`);

  console.log(`${await person.givenName} is friends with:`);
  for await (const name of person.friends.givenName)
    console.log(`- ${name}`);
}

Inspecting the generated path expression

(async person => {
  console.log(await person.friends.givenName.pathExpression);
})(ruben);

Getting all subjects of a document

(async document => {
  for await (const subject of document.subjects)
    console.log(`${subject}`);
})(ruben);

Getting all properties of a subject

(async subject => {
  for await (const property of subject.properties)
    console.log(`${property}`);
})(ruben);

Converting an LDflex expression into a SPARQL query

(async person => {
  console.log(await person.friends.givenName.sparql);
})(ruben);

Sorting path results

(async person => {
  for await (const uri of person.interest.sort('label'))
    console.log(`- ${uri}`);
})(ruben);

The sort function takes multiple arguments, creating a path that sorts on the last argument. The path can also continue after the sort: person.friends.sort('country', 'label').givenName will sort the friends based on the label of their country, and then return their names.

Modifying data

// Add a new value
await person['http://xmlns.com/foaf/0.1/name'].add(literal(name));
await person['http://xmlns.com/foaf/0.1/nick'].add(literal(nickname));

// Set a new value and override existing values
await person['http://xmlns.com/foaf/0.1/name'].set(literal(name));
await person['http://xmlns.com/foaf/0.1/nick'].set(literal(nickname));

// Delete object values
await person['http://xmlns.com/foaf/0.1/name'].delete();
await person['http://xmlns.com/foaf/0.1/nick'].delete();

// Replace object values
await person['http://xmlns.com/foaf/0.1/name'].replace(literal(oldName), literal(name));

Accessing collections

Handle rdf:List, rdf:Bag, rdf:Alt, rdf:Seq and rdf:Container.

For rdf:Lists

(async publication => {
  // Returns an Array of Authors
  const authors = await publication['bibo:authorList'].list();
})(ordonez_medellin_2014);

For rdf:Alt, rdf:Seq and rdf:Containers

(async data => {
  // Returns an Array of elements
  const elements = await data['ex:myContainer'].container();
})(data);

For rdf:Bags

(async data => {
  // Returns a Set of elements
  const elements = await data['ex:myBag'].containerAsSet();
})(data);

Alternatively, .collection can be used for any collection (i.e. rdf:List, rdf:Bag, rdf:Alt, rdf:Seq and rdf:Container) provided the collection has the correct rdf:type annotation in the data source

(async publication => {
  // Returns an Array of Authors
  const authors = await publication['bibo:authorList'].collection();
})(ordonez_medellin_2014);

NamedNode URI utilities

ruben.namespace // 'https://ruben.verborgh.org/profile/#'
ruben.fragment // 'me'
await ruben.prefix // 'rbn'

Additional Handlers

The following libraries provide handlers that extend the functionality of LDflex:

• async-iteration-handlers Provides methods such as .map, .filter and .reduce for the async-iterable results returned by LDflex.

License

©2018–present Ruben Verborgh, Ruben Taelman. MIT License.

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