Implement Create Schema RPC on node

[Vishwas1]

Introduction

The Credential Schema is a document that is used to guarantee the structure, and by extension the semantics, of the set of claims comprising a Verifiable Credential. A shared Credential Schema allows all parties to reference data in a known way.

4 Perspective of schema

1. Author: An author creates a schema as a blueprint for a verifiable credential, specifying the shape and format of the data in such a credential.
2. Issuer: utilize schemas to provide structure and meaning to the data they issue as verifiable credentials.
3. Verifier: A schema always guarantees the structure of a credential. The described structure can be used by the Verifier to understand what data the Holder holds.
4. Holder: Holders, or those who are the subject of credential issuance, can make sense of the data they own -- values -- by viewing it against a schema -- keys.

Credential Schemas are created and made available as immutable objects on a distributed ledger.

** id **

A globally unique identifier to locate the schema on a distributed ledger. This identifier is a Generic DID Parameter Name based upon the author of the schema. For example, if the author had a did like

did:work:abcdefghi

Metadata

• type
• modelVersion
• id
• schemaVersion
• name
• author
• authored

A possible schema ID the author created would have ID such as:

did:work:abcdefghi;id=17de181feb67447da4e78259d92d0240;version=1.0

Example

{
  "type": "https://w3c-ccg.github.io/vc-json-schemas/schema/1.0/schema.json",
  "modelVersion": "1.0",
  "id": "did:work:MDP8AsFhHzhwUvGNuYkX7T;id=06e126d1-fa44-4882-a243-1e326fbe21db;version=1.0",
  "name": "EmailCredentialSchema",
  "author": "did:work:MDP8AsFhHzhwUvGNuYkX7T",
  "authored": "2018-01-01T00:00:00+00:00",
  "schema": {
    "$schema": "http://json-schema.org/draft-07/schema#",
    "description": "Email",
    "type": "object",
    "properties": {
      "emailAddress": {
        "type": "string",
        "format": "email"
      }
    },
    "required": ["emailAddress"],
    "additionalProperties": false
  },
  "proof": {
      "created": "2019-09-27T06:26:11Z",
      "creator": "did:work:MDP8AsFhHzhwUvGNuYkX7T#key-1",
      "nonce": "0efba23d-2987-4441-998e-23a9d9af79f0",
      "signatureValue": "2A7ZF9f9TWMdtgn57Y6dP6RQGs52xg2QdjUESZUuf4J9BUnwwWFNL8vFshQAEQF6ZFBXjYLYNU4hzXNKc3R6y6re",
      "type": "Ed25519VerificationKey2018"
  }
}

Versioning

Revision
The addition or removal of an optional field is what constitutes a REVISION. Read more https://w3c-ccg.github.io/vc-json-schemas/v1/index.html#revision

Model

When a schema breaks historical data we call it a model change. The most common case of a MODEL change is the addition or subtraction of a required field.

An example of this rule is when the additionalProperties field’s value changes. Changing additionalProperties from false to true OR from true to false constitutes a breaking change, necessitating a MODEL increment.

This line was wrritten in https://hyperledger-indy.readthedocs.io/projects/node/en/latest/transactions.html#schema not sure why?

It’s not possible to update an existing schema. So, if the Schema needs to be evolved, a new Schema with a new version or new name needs to be created.

Reference

• https://w3c-ccg.github.io/vc-json-schemas/v1/index.html
• https://lists.w3.org/Archives/Public/public-credentials/2019Oct/att-0008/workday-credential-schemas.pdf
• https://hyperledger-indy.readthedocs.io/projects/node/en/latest/transactions.html#schema
• https://docs.serto.id/docs/main-concepts/schemas/
• https://schemas.serto.id/

[Vishwas1]

Example schema https://ssi.hypermine.in/core/api/v1/schema/sch_f3ab4b78-48fa-4a4d-9fe4-8f06dc501a6b

Schema Proto

https://w3c-ccg.github.io/vc-json-schemas/v1/index.html#credential_schema_definition_metadata

Schema: {
  type: string
  modelVersion: string
  id: string
  name: string
  author: string
  authored: string
  schema: SchemaProto
}

Schema Property Proto

https://w3c-ccg.github.io/vc-json-schemas/v1/index.html#credential_schema_definition_schema

ScheamProperty :{ 
  $schema: string / any
  description: string
  properties: string / any
  required: array
  additionalProperties: boolean
}

RPC

createSchema(Schema schema, Signatures  sig)

Validation

Validate basic format of shchema

Validate the format of id field

<did>;id=<guid>;version=<version>

example:

did:work:abcdefghi;id=17de181feb67447da4e78259d92d0240;version=1.0

did:work:abcdefghi;id=17de181feb67447da4e78259d92d0240;version=1.1

Validate Signature

1. Get the author (did) from schema
2. Get the the didDoc and publickey of the author
3. If the didDoc does nto exists error => author did does not exists
4. verify signature using the public key present in the did

Store the schema

key

id=17de181feb67447da4e78259d92d0240

value

schema

[arnabghose997]

The PR (#49) has been merged. The details of test cases are updated in the PR