JarCastingLDflex 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",
}
};
// 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.
License
©2018–present Ruben Verborgh, Ruben Taelman. MIT License.