Disco Schemas

These are JSON Schemas that define Verifiable Credentials.

Available schemas can be found in the json/ directory and can either be referenced directly from this git repo by their URL (e.g. https://raw.githubusercontent.com/discoxyz/disco-schemas/main/json/AccountLinkageCredential/1-0-0.json) or can be imported from this package.

Installation

yarn add disco-schemas
# or
npm install disco-schemas

Example usage

import {
  validateVcAgainstSchema,
  getAndValidateSchemaFromVc,
  AccountLinkageCredential,
  EXAMPLE_VC,
} from "disco-schemas";

(async function () {
  let valid, errors, schema;

  // Validate against a particular schema
  ({ valid, errors } = await validateVcAgainstSchema(EXAMPLE_VC, AccountLinkageCredential));
  console.log("VC is valid according to schema:", valid);
  console.log("Validation errors:", errors);

  // Validate against the schema the VC references in its `credentialSchema` field, and return that schema
  ({ valid, errors, schema } = await getAndValidateSchemaFromVc(EXAMPLE_VC));
  console.log("VC references schema:", schema);
  console.log("VC is valid according to schema:", valid);
  console.log("Validation errors:", errors);

  // Example validation error
  delete EXAMPLE_VC.credentialSubject.username;
  ({ valid, errors } = await validateVcAgainstSchema(EXAMPLE_VC, AccountLinkageCredential));
  console.log("VC is valid according to schema:", valid);
  console.log("Validation errors:", errors);
})();

Referencing schemas in a Verifiable Credential

The credentialSchema property can hold a reference to a JSON Schema by its URL. For example:

{
  "@context": ["https://www.w3.org/2018/credentials/v1"],
  type: ["VerifiableCredential", "AccountLinkageCredential"],
  ...
  credentialSubject: { ... },
  credentialSchema: {
    id: "https://raw.githubusercontent.com/discoxyz/disco-schemas/main/json/AccountLinkageCredential/1-0-0.json",
    type: "JsonSchemaValidator2018",
  },
}

The addSchemaToVc function can be used to automatically add the credentialSchema field and, optionally, append its name to type (note: adding to type this way is not strictly compliant with the VC standard, which requires that type values must dereference to a URI via the JSON-LD @context).

Versioning

Schema objects exported by this package always use the latest version, but schema JSON is available both at versioned URLs and at a pointer to the latest version:

Versions are defined as MODEL-REVISION-ADDITION. See https://docs.snowplowanalytics.com/docs/pipeline-components-and-applications/iglu/common-architecture/schemaver/ for more info.

Development

First, install Yarn and then install dependencies:

yarn install

Adding a new schema

See the JSON Schema introduction for information about the standard, and you can use this online editor to try editing JSON Schema live.

To add a new schema:

Determine the schema title and folder name
- The title should end in " Credential" and the folder should be a PascalCase version of that title
- E.g. title "Event Ticket Credential" -> folder "EventTicketCredential"
- This follows the VC standard's type naming convention
Create a folder in src/schemas/ for your new schema with the PascalCase folder name
Copy a schema version from another schema into this folder. Call it 1-0-0.ts for the first version
Update the schema! Make sure to change the following values:
- $id - replace the schema name and version at the end of this URL with the folder name and version number
- title (required) and description (required)
- credentialSubject your schema goes here!
Add to the schema to src/schemas/index.ts
- Import and export the schema
- (Optional: add to issuableSchemas if it should be available from Disco app) <- We don't need to do this anymore!!
Make sure to run yarn generate before using the schema or committing changes

Adding a new version of a schema

Each schema has a version number "MODEL-REVISION-ADDITION", e.g. "2-1-7". See the Versioning section for more information.

To add a new version:

Copy the last version to a new .ts file
Change the $id URL to match the new version number
Make your changes
Make sure to run yarn generate before using the schema or committing changes
package.json version will update on merge depending on the commit log
- minor chore: Description , fix: Description
- major feat: Description
- While schemas are permanently available at versioned .json URLs, schemas exported by this module in code always refer to the latest version, so apps importing any changed schemas will get the updates when they update disco-schemas. As such, make sure to follow SemVer conventions when updating package.json version number.

Notes

The JSON Schema standard allows the addition of arbitrary properties, so one could for instance add a $metadata object into a schema definition if desired.
Every schema currently builds off of BaseVerifiableCredential version 1-0-0. If a new version of that base schema is needed, schemas that need those updates should make sure to import the new version of it.