RDF Object
RDF Object makes it easier to read RDF data by loading it as JSON objects.
This library accepts RDFJS-compliant quads.
Installation
$ yarn install rdf-object
This package also works out-of-the-box in browsers via tools such as webpack and browserify.
Require
import {RdfObjectLoader} from "rdf-object";
or
const RdfObjectLoader = require("rdf-object").RdfObjectLoader;
Usage
RdfObjectLoader
accepts RDF quad/triple streams (or arrays) as input,
and loads the resulting graph in-memory as linked Resource
s.
A Resource
is a wrapper over an RDFJS term that holds property links.
Using a JSON-LD context,
properties are easily accessible.
Examples
The following examples assume the following imports:
import {namedNode, literal, triple} from "@rdfjs/data-model"; // External library
import {RdfObjectLoader} from "rdf-object";
Create an object loader
RdfObjectLoader
accepts a JSON-LD context as input argument.
This context can also be the URL to a JSON-LD context.
// Initialize our loader with a JSON-LD context
const context = {
'rdf': 'http://www.w3.org/1999/02/22-rdf-syntax-ns#',
'rdfs': 'http://www.w3.org/2000/01/rdf-schema#',
'type': 'rdf:type',
'label': 'rdfs:label',
'foaf': 'http://xmlns.com/foaf/0.1/',
'knows': 'foaf:knows',
'name': 'foaf:name',
'ex': 'http://example.org/'
};
const myLoader = new RdfObjectLoader({ context });
Get resources after importing
Resources are stored inside the resources
field of RdfObjectLoader
,
they are indexed by URI.
Each resource has the following fields:
value
: The term value. For example a URI or literal value.type
: The RDFJS term type.term
: The RDFJS term.
// Import triples
myLoader.importArray([
triple(namedNode('http://example.org/myResource'), namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#type'), namedNode('http://example.org/Resource')),
]).then(() => {
// Get property values by shortcut
const myResource = myLoader.resources['http://example.org/myResource'];
console.log(`URI: ${myResource.value}`);
console.log(`Term type: ${myResource.type}`);
console.log(`Term value: ${myResource.value}`);
console.log(`Term: ${myResource.term}`);
});
Alternatively, myLoader.import()
can be invoked on
an RDFJS stream of triples/quads.
This can for example accept parsed turtle streams.
Multiple calls to importArray
and import
can be done at any time
to easily combined multiple sources.
Get properties by shortcut
The property
field on a Resource
contains all property values.
It maps all predicates to objects,
where each predicate is a URI or JSON-LD shortcut,
and each object is a Resource
.
If multiple values are present for that property, only the first will be returned.
// Import triples
myLoader.importArray([
triple(namedNode('http://example.org/myResource'), namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#type'), namedNode('http://example.org/Resource')),
triple(namedNode('http://example.org/myResource'), namedNode('http://www.w3.org/2000/01/rdf-schema#label'), literal('My Resource')),
]).then(() => {
// Get property values by shortcut
const myResource = myLoader.resources['http://example.org/myResource'];
console.log(`URI: ${myResource}`);
console.log(`Type: ${myResource.property.type}`);
console.log(`Label: ${myResource.property['rdfs:label']}`);
console.log(`Label (bis): ${myResource.property['http://www.w3.org/1999/02/22-rdf-syntax-ns#label']}`);
});
Get multiple property values
Via the properties
field on Resource
,
all values of a property can be retrieved.
JSON-LD can also be used on properties
.
// Import triples
myLoader.importArray([
triple(namedNode('http://example.org/myResource'), namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#type'), namedNode('http://example.org/Resource')),
triple(namedNode('http://example.org/myResource'), namedNode('http://www.w3.org/2000/01/rdf-schema#label'), literal('My Resource')),
]).then(() => {
// Get property values by shortcut
const myResource = myLoader.resources['http://example.org/myResource'];
console.log(`Labels: ${myResource.properties.label}`);
});
The raw properties (without JSON-LD shortcuts) are
available in the propertiesUri
field on Resource
.
Set properties by shortcut
The property
and properties
field can also be used to set new values on a resource.
For example:
// Sets a single property value
myResource.property['rdfs:label'] = new Resource({ term: literal('Name') });
// Sets multiple property values
myResource.properties['rdfs:label'].push(new Resource({ term: literal('Name 1') }));
myResource.properties['rdfs:label'].push(new Resource({ term: literal('Name 2') }));
Resources are nested
As Resource
properties map to other Resource
s,
nested property paths can be followed easily.
// Import triples
myLoader.importArray([
triple(namedNode('https://www.rubensworks.net/#me'), namedNode('http://xmlns.com/foaf/0.1/knows'), namedNode('https://ruben.verborgh.org/profile/#me')),
triple(namedNode('https://www.rubensworks.net/#me'), namedNode('http://xmlns.com/foaf/0.1/knows'), namedNode('https://data.verborgh.org/people/joachim_van_herwegen')),
triple(namedNode('https://www.rubensworks.net/#me'), namedNode('http://xmlns.com/foaf/0.1/name'), literal('Ruben Taelman')),
triple(namedNode('https://ruben.verborgh.org/profile/#me'), namedNode('http://xmlns.com/foaf/0.1/name'), literal('Ruben Verborgh')),
triple(namedNode('https://data.verborgh.org/people/joachim_van_herwegen'), namedNode('http://xmlns.com/foaf/0.1/name'), literal('Joachim Van Herwegen')),
]).then(() => {
// Get friend names via nested resources
const rubenT = myLoader.resources['https://www.rubensworks.net/#me'];
console.log(`Friends of ${rubenT.property.name}:`);
for (const friend of rubenT.properties.friends) {
console.log(`* ${friend.property.name}`);
}
});
Conveniently access RDF lists
RDF lists are automatically parsed
and exposed as a JavaScript array via the
list
field on Resource
.
// Import triples
myLoader.importArray([
triple(namedNode('http://example.org/myResource'), namedNode('http://example.org/list'), namedNode('http://example.org/myList0')),
triple(namedNode('http://example.org/myList0'), namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#first'), literal('A')),
triple(namedNode('http://example.org/myList0'), namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#rest'), namedNode('http://example.org/myList1')),
triple(namedNode('http://example.org/myList1'), namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#first'), literal('B')),
triple(namedNode('http://example.org/myList1'), namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#rest'), namedNode('http://example.org/myList2')),
triple(namedNode('http://example.org/myList2'), namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#first'), literal('C')),
triple(namedNode('http://example.org/myList2'), namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#rest'), namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#nil')),
]).then(() => {
// Get friend names via nested resources
const myResource = myLoader.resources['http://example.org/myResource'];
console.log(`List values of ${myResource}`);
for (const listElement of myResource.property['ex:list'].list) {
console.log(`* ${listElement}`);
}
});
If you don't want RDF lists to be parsed automatically,
you can set normalizeLists
to false
in the RdfObjectLoader
constructor.
Conveniently construct Resources
If you want to create custom Resources yourself, for example during testing, then you can create them for any given term:
myLoader.getOrMakeResource(namedNode('ex:myResource'));
Alternatively, you can use createCompactedResource
to easily create a resource with compacted properties:
myLoader.createCompactedResource({
'@id': 'http://example.org/myId',
propertyLiteral: '"abc"',
propertyWithList: {
list: [
'"abc"'
]
},
propertyWithNestedHash: {
nestedProperty: {
'@id': 'http://example.org/mySubId',
}
},
propertyWithResource: myLoader.getOrMakeResource(namedNode('ex:myResource')),
});
Special field cases:
- '@id' represents the IRI identifier.
- 'list' is considered an RDF list.
Values can be nested hashes, for which other Resources will be created. String values will be converted into term sources following the semantics of rdf-string.js. Values can also be Resources or RDF/JS terms.
createCompactedResources
is equivalent, but accepts an array (or hash) as input,
and converts it into an array of resources.
License
This software is written by Ruben Taelman.
This code is released under the MIT license.