Aries RFC 0249: Aries SDK Rich Schema Contexts

• Authors: Brent Zundel, Ken Ebert
• Status: PROPOSED
• Since: 2019-10-08
• Status Note: Part of proposed Rich Schema capabilities for credentials
• Supersedes:
• Start Date: 2019-06-07
• Tags: feature, rich-schemas

Summary

Every rich schema object has an associated @context. Contexts are JSON objects. They are the standard mechanism for defining shared semantic meaning among rich schema objects.

Motivation

@context is JSON-LD’s namespacing mechanism. Contexts allow rich schema objects to use a common vocabulary when referring to common attributes, i.e. they provide an explicit shared semantic meaning.

Tutorial

Intro to @context

@context is a JSON-LD construct that allows for namespacing and the establishment of a common vocabulary.

Data Registry Storage

Aries-SDK will provide a means for writing @context objects to and reading @context objects from a data registry (such as a distributed ledger).

Example context

"@context": [
    "did:sov:UVj5w8DRzcmPVDpUMr4AZhJ:7:example:1.0",
    "did:sov:AZKWUJ3zArXPG36kyTJZZm:7:base-context:1.0",
    "did:sov:9TDvb9PPgKQUWNQcWAFMo4:7:new-person:3.5",
    {
          "dct": "http://purl.org/dc/terms/",
          "rdf": "http://www.w3.org/1999/02/22-rdf-syntax-ns#",
          "rdfs": "http://www.w3.org/2000/01/rdf-schema#",
          "Driver": "did:sov:35qJWkTM7znKnicY7dq5Yk:8:driver:2.4",
          "DriverLicense": "did:sov:Q6kuSqnxE57waPFs2xAs7q:8:driver-license:3.5",
          "CategoryOfVehicles": "DriverLicense:CategoryOfVehicles"
    }
]

Aries Data Registry Interface

We propose adding two Aries-Data-Registry-Interface methods for writing and reading @context objects:

• write_context: a method to write a @context object to a data registry.
• read_context: a method to read a @context object from a data registry.

write_context

Writes a context to a data registry.

#Params
submitter: {
    key: public key of the submitter,
    keystore: key manager where private key is stored
}, 
data: {
    id: identifier for the context,
    context: context object,
    name: context name string,
    version: context version string,
    ver: version of the context JSON format
},
registry: identifier for the registry

#Returns
registry_response: result as json,
error: {
    code: aries common error code,
    description:  aries common error description
}

read_context

Reads a context from a data registry.

#Params
submitter (optional): {
    key: public key of the submitter,
    keystore: key manager where private key is stored
}, 
id: identifier for the context,
registry: identifier for the registry

#Returns
registry_response: context object,
error: {
    code: aries common error code,
    description:  aries common error description
}

Reference

More information on the Verifiable Credential data model use of @context may be found here

More information on @context from the JSON-LD specification may be found here and here.

Drawbacks

There are no known drawbacks.

Rationale and alternatives

• A @context object is required by the W3C Verifiable Credentials Data Model specification.
• It also supports rich schema capabilities for credentials.

Unresolved questions

• Is the proposed interface generic enough to support other data registries?

Implementations

The following lists the implementations (if any) of this RFC. Please do a pull request to add your implementation. If the implementation is open source, include a link to the repo or to the implementation within the repo. Please be consistent in the "Name" field so that a mechanical processing of the RFCs can generate a list of all RFCs supported by an Aries implementation.

Name / Link	Implementation Notes