CaSS Docs

# JSON-LD, RDF Formats

CaSS uses JSON-LD (opens new window) for data storage. JSON-LD is a simple, light-weight data format that's also parsable as standard JSON. It exists to provide a standard for holding 'Linked Data' (LD), which you can think of as meaning links to data (usually in place of the data itself) as values inside standard JSON objects.

JSON-LD is a compromise between rich data modeling formats such as Turtle and RDF-JSON and the much simpler, easier to use JSON. JSON-LD has many layers of complexity that should be unwrapped slowly. This guide will discuss a few of them necessary to use CASS.

# In a Nutshell

A JSON-LD object is a JSON object that also holds

  1. A type (@type)
  2. An identifier (@id)

JSON Object

{
    "name": "Bob"
}

JSON-LD Object

{
    "@type":                  "http://schema.org/Person",
    "@id":                    "http://dev.cassproject.org/api/data/Bob",
    "http://schema.org/name": "Bob"
}

Keep in mind:

  • All references to fields or objects in JSON-LD are URLs, instead of IDs or long pointers.
  • A JSON-LD object should be stored and retrievable at the location indicated by its @id (commonly just ‘id’).
  • Navigating to any URL should give you enough information to use the object.

# Context

To make life simpler, the @context field either provides something similar to a namespace or a link to a document that describes a namespace. This has the benefit of providing meaning to things like shortened fields.

{
    "@context": "http://schema.cassproject.org/0.3",
    "@type":    "http://schema.org/Person",
    "@id":      "http://dev.cassproject.org/api/data/Bob",
    "name":     "Bob"
}

The field ‘name’ is specified by the namespace to mean ‘http://schema.org/name (opens new window)’. These allow JSON-LD documents to be more tractable to developers.

# With Security

CASS includes an extension to JSON-LD called KBAC that provides additional meta-fields (prefixed with @) that allow objects to be permissioned using Public Key Cryptography.

In short:

  • The @owner field defines key-holders who can modify or delete an object
  • The @reader field defines key-holders who can read an object’s hidden and encrypted fields
  • The @signature field defines signatures that can be used to validate the integrity of the data

These fields can be found in any CASS object, such as this one (opens new window).

# Resources

JSON-LD is aligned with RDF, which is an advanced data modeling paradigm and methodology that will not be covered here. Reading the JSON-LD specification is a good start, but the CASS Library attempts to insulate you from RDF as much as possible.

# Other RDF Formats

Other RDF formats may be negotiated through use of the Accept header in an HTTP GET request. Supported formats are:

text/n4

text/turtle

application/x-turtle

application/rdf+xml

application/rdf+n4

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