JSON-LD is an extension of JSON , it is a standard way of avoiding ambiguity when expressing linked data in JSON so that the data is structured in a format which is parsable by machines. It is a method of ensuring that all data attributes can be easily compared when coming from a multitude of separate data sources, which could have a different idea as to what each attribute means. For example, when two data entities have a name attribute how can the computer be certain that is refers to a "Name of a thing" in the same sense (rather than a Username or a Surname or something). URLs and data models are used to remove ambiguity by allowing attributes to have a both short form (such as name) and a fully specified long form (such http://schema.org/name) which means it is easy to discover which attribute have a common meaning within a data structure.
JSON-LD introduces the concept of the @context element which provides additional information allowing the computer to interpret the rest of the data with more clarity and depth.
Furthermore the JSON-LD specification enables you to define a unique @type associating a well-defined data model to the data itself.
JSON-LD is designed around the concept of a "context" to provide additional mappings from JSON to an RDF model. The context links object properties in a JSON document to concepts in an ontology. In order to map the JSON-LD syntax to RDF, JSON-LD allows values to be coerced to a specified type or to be tagged with a language. A context can be embedded directly in a JSON-LD document or put into a separate file and referenced from different documents (from traditional JSON documents via an HTTP Link header).
{
"@context": {
**"name"**: "<http://xmlns.com/foaf/0.1/name>",
**"homepage"**: {
"@id": "<http://xmlns.com/foaf/0.1/workplaceHomepage>",
"@type": "@id"
},
**"Person"**: "<http://xmlns.com/foaf/0.1/Person>"
},
"@id": "<https://me.example.com>",
"@type": "Person",
**"name"**: "John Smith",
**"homepage"**: "<https://www.example.com/>"
}
The example above describes a person, based on the FOAF vocabulary. First, the two JSON properties name and homepage and the type Person are mapped to concepts in the FOAF vocabulary and the value of the homepage property is specified to be of the type @id, i.e., it is specified to be an IRI in the context definition. Based on the RDF model, this allows the person described in the document to be unambiguously identified by an IRI. The use of resolvable IRIs allows RDF documents containing more information to be transcluded which enables clients to discover new data by simply following those links; this principle is known as Follow Your Nose.
By having all data semantically annotated as in the example, an RDF processor can identify that the document contains information about a person (@type) and if the processor understands the FOAF vocabulary it can determine which properties specify the person’s name and homepage.
{
"@context": "<https://json-ld.org/contexts/person.jsonld>",
"@id": "<http://dbpedia.org/resource/John_Lennon>",
"name": "John Lennon",
"born": "1940-10-09",
"spouse": "<http://dbpedia.org/resource/Cynthia_Lennon>"
}