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DID & DDO Specification of decentralized identifiers for assets in Ocean Protocol using the DID & DDO standards. /concepts/did-ddo/ concepts

v4.0.0

Overview

This document describes how Ocean assets follow the DID/DDO specification, such that Ocean assets can inherit DID/DDO benefits and enhance interoperability. DIDs and DDOs follow the specification defined by the World Wide Web Consortium (W3C).

Decentralized identifiers (DIDs) are a type of identifier that enable verifiable, decentralized digital identity. Each DID is associated with a unique entity and DIDs may represent humans, objects, and more.

A DID Document (DDO) is JSON blob that holds information about the DID. Given a DID, a resolver will return the DDO of that DID.

If a DID is the index key in a key-value pair, then the DID Document is the value to which the index key points. The combination of a DID and its associated DID Document forms the root record for a decentralized identifier.

Rules for DIDs & DDOs

An asset in Ocean represents a downloadable file, compute service, or similar. Each asset is a resource under control of a publisher. The Ocean network itself does not store the actual resource (e.g. files).

An asset should have a DID and DDO. The DDO should include metadata about the asset, and define access in at least one service. The DDO can only be modified by owners or delegated users.

A metadata cache like Aquarius can help in reading and searching through encrypted DDO data from the chain.

Publishing & Retrieving DDOs

The DDO is stored on-chain as part of the NFT contract and it is stored encrypted using the private key of the Provider. To resolve it, a metadata cache like Aquarius must query the provider to decrypt the DDO.

Here is the complete flow:

DDO_flow

title DDO flow

User(Ocean library) -> User(Ocean library): Prepare DDO
User(Ocean library) -> Provider: encrypt DDO
Provider -> User(Ocean library): encryptedDDO
User(Ocean library) -> ERC721 contract: publish encryptedDDO
Aquarius <-> ERC721 contract: monitors ERC721 contract and gets MetdadataCreated Event (contains encryptedDDO)
Aquarius -> ERC721 contract: calls getMetaData()
Aquarius -> Provider: decrypt encryptedDDO, signed request using Aquarius's private key
Provider -> ERC721 contract: checks state using getMetaData()
Provider -> Provider: depending on metadataState (expired,retired) and aquarius address, validates the request
Provider -> Aquarius: DDO
Aquarius -> Aquarius : validate DDO
Aquarius -> Aquarius : cache DDO
Aquarius -> Aquarius : enhance cached DDO in response with additional infos like `events` & `stats`

DID

In Ocean, a DID is a string that looks like:

did:op:0ebed8226ada17fde24b6bf2b95d27f8f05fcce09139ff5cec31f6d81a7cd2ea

where

0ebed8226ada17fde24b6bf2b95d27f8f05fcce09139ff5cec31f6d81a7cd2ea = sha256(ERC721 contract address + chainId)

It follows the generic DID scheme.

DDO

A DDO in Ocean has these required attributes:

Attribute Type Description
@context Array of string Contexts used for validation.
id string Computed as sha256(address of ERC721 contract + chainId).
version string Version information referring to this DDO spec version, like 4.0.0.
chainId number Stores chainId of the network the DDO was published to.
created ISO Date Time string Contains the date of publishing in ISO Date Time Format, e.g. 2000-10-31T01:30:00.
updated ISO Date Time string Contains the the date of last update in ISO Date Time Format, e.g. 2000-10-31T01:30:00.
services Services Stores an array of services defining access to the asset.
files Files Stores information about the asset's files.
encryptedFiles Files Added after publishing.
credentials Credentials Describes the credentials needed to access a dataset in addition to the services definition.

Metadata

This object holds information describing the actual actual asset.

Attribute Type Required Description
description string ✓ Details of what the resource is. For a dataset, this attribute explains what the data represents and what it can be used for.
copyrightHolder string The party holding the legal copyright. Empty by default.
name string ✓ Descriptive name or title of the asset.
type string ✓ Asset type. Includes "dataset" (e.g. csv file), "algorithm" (e.g. Python script). Each type needs a different subset of metadata attributes.
author string ✓ Name of the entity generating this data (e.g. Tfl, Disney Corp, etc.).
license string ✓ Short name referencing the license of the asset (e.g. Public Domain, CC-0, CC-BY, No License Specified, etc. ). If it's not specified, the following value will be added: "No License Specified".
links Array of string Mapping of URL strings for data samples, or links to find out more information. Links may be to either a URL or another asset.
contentLanguage string The language of the content. Use one of the language codes from the IETF BCP 47 standard
categories Array of string Optional array of categories associated to the asset. Note: recommended to use tags instead of this.
tags Array of string Array of keywords or tags used to describe this content. Empty by default.
additionalInformation Object Stores additional information, this is customizable by publisher
algorithm Algorithm Metadata ✓ (for algorithm assets only) Information about asset of type algorithm

Example:

{
  "metadata": {
    "description": "Sample description",
    "name": "Sample asset",
    "type": "dataset",
    "author": "OPF",
    "license": "https://market.oceanprotocol.com/terms"
  }
}

Algorithm Metadata

An asset of type algorithm has the following additional attributes under algorithm within the metadata object:

Attribute Type Required Description
language string Language used to implement the software
version string Version of the software.
container container ✓ Object describing the Docker container image. See below

The container object has the following attributes defining the Docker image the algorithm needs to run:

Attribute Type Required Description
entrypoint string ✓ The command to execute, or script to run inside the Docker image.
image string ✓ Name of the Docker image.
tag string ✓ Tag of the Docker image.
checksum string ✓ Checksum of the Docker image. 
{
  "metadata": {
    "description": "Sample description",
    "name": "Sample algorithm asset",
    "type": "algorithm",
    "author": "OPF",
    "license": "https://market.oceanprotocol.com/terms",
    "algorithm": {
      "language": "",
      "version": "",
      "container": {
        "entrypoint": "",
        "image": "",
        "tag": "",
        "checksum": ""
      }
    }
  }
}

Files

The ddo.files field is returned as a string which holds the encrypted file URLs. During the publish process this needs to be encrypted with a respective Provider API call.

Example:

{
  "files": "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"
}

Services

Services define the access to the asset.

Attribute Type Required Description
type string ✓ Type of service (access, compute, wss, etc.
name string Service friendly name
description string Service description
datatokenAddress string ✓ Datatoken address
providerEndpoint string ✓ Provider endpoint URI (URI + path)
timeout number ✓ describing how long the service can be used after consumption is initiated. A timeout of 0 represents no time limit. Expressed in seconds.
files string, see Files ✓ Encrypted file URLs
privacy Privacy ✓ (for compute assets only) If asset service is of type compute, holds information about the compute-related privacy settings.

Compute Privacy

An asset with a service of type compute has the following additional attributes under the privacy object. This object is required if the asset is of type compute, but can be omitted for type of access.

Attribute Type Required Description
allowRawAlgorithm boolean ✓ If true, a drag & drop algorithm can be run
allowNetworkAccess boolean ✓ If true, the algorithm job will have network access (still WIP)
publisherTrustedAlgorithmPublishers Array of String ✓ If empty, then any published algorithm is allowed. Otherwise, only published algorithms by some publishers are allowed
publisherTrustedAlgorithms Array of publisherTrustedAlgorithms ✓ If empty, then any published algorithm is allowed. (see below)

The publisherTrustedAlgorithms is an array of objects with the following structure:

Attribute Type Required Description
did string ✓ The DID of the algorithm which is trusted by the publisher.
filesChecksum string ✓ Hash of algorithm's encryptedFiles + files section (as string)
containerSectionChecksum string ✓ Hash of the algorithm container section (as string)

To produce filesChecksum:

sha256(
  algorithm_ddo.metadata.encryptedFiles +
    JSON.Stringify(algorithm_ddo.metadata.files)
)

To produce containerSectionChecksum:

sha256(JSON.Stringify(algorithm_ddo.metadata.algorithm.container))

Example:

{
  "services": [
    {
      "type": "access",
      "name": "Download service",
      "description": "Download service",
      "datatokenAddress": "0x123",
      "providerEndpoint": "https://myprovider",
      "timeout": 0
    },
    {
      "type": "compute",
      "name": "Compute service",
      "description": "Compute service",
      "datatokenAddress": "0x124",
      "providerEndpoint": "https://myprovider",
      "timeout": 0,
      "privacy": {
        "allowRawAlgorithm": false,
        "allowNetworkAccess": true,
        "publisherTrustedAlgorithmPublishers": ["0x234", "0x235"],
        "publisherTrustedAlgorithms": [
          {
            "did": "did:op:123",
            "filesChecksum": "100",
            "containerSectionChecksum": "200"
          },
          {
            "did": "did:op:124",
            "filesChecksum": "110",
            "containerSectionChecksum": "210"
          }
        ]
      }
    }
  ]
}

Credentials

By default, a consumer can access a resource if they have 1.0 datatokens. Credentials allow the publisher to optionally specify finer-grained permissions.

Consider a medical data use case, where only a credentialed EU researcher can legally access a given dataset. Ocean supports this as follows: a consumer can only access the resource if they have 1.0 datatokens and one of the specified "allow" credentials.

This is like going to an R-rated movie, where you can only get in if you show both your movie ticket (datatoken) and some some id showing you're old enough (credential).

Only credentials that can be proven are supported. This includes Ethereum public addresses, and (in the future) W3C Verifiable Credentials and more.

Ocean also supports "deny" credentials: if a consumer has any of these credentials, they can not access the resource.

Here's an example object with both "allow" and "deny" entries:

{
  "credentials": {
    "allow": [
      {
        "type": "address",
        "values": ["0x123", "0x456"]
      }
    ],
    "deny": [
      {
        "type": "address",
        "values": ["0x2222", "0x333"]
      }
    ]
  }
}

For future usage, we can extend that with different credentials types.

Example:

{
  "type": "credential3Box",
  "values": ["profile1", "profile2"]
}

DDO Hash

In order to ensure the integrity of the DDO, a hash is computed for each DDO:

const hash = sha256(JSON.stringify(DDO))

The hash is used when publishing/update metadata using setMetaData function in the ERC721 contract, and is stored in the event generated by the ERC721 contract:

event MetadataCreated(
  address indexed createdBy,
  uint8 state,
  string decryptorUrl,
  bytes flags,
  bytes data,
  bytes metaDataHash,
  uint256 timestamp,
  uint256 blockNumber
);

event MetadataUpdated(
  address indexed updatedBy,
  uint8 state,
  string decryptorUrl,
  bytes flags,
  bytes data,
  bytes metaDataHash,
  uint256 timestamp,
  uint256 blockNumber
);

Aquarius should always check the hash after data is decrypted via a Provider API call, in order to ensure DDO integrity.

State

Each asset has a state, which is held by the NFT contract. The possible states are:

  • 0 = active
  • 1 = end-of-life
  • 2 = deprecated (by another asset)
  • 3 = revoked by publisher

Aquarius Enhanced DDO Response

The following fields are added by Aquarius in its DDO response for convenience reasons where an Asset returned by Aquarius inherits the DDO fields from the chain.

These additional fields are never stored on-chain, and are never taken into consideration when hashing the DDO.

NFT

The nft object contains information about the NFT contract which represents the intellectual property of the publisher.

Attribute Type Description
address string Contract address of the deployed NFT contract
name string Name of NFT set in contract
symbol string Symbol of NFT set in contract
owner string ETH account address of the NFT owner

Example:

{
  "nft": {
    "adddress": "0x000000",
    "name": "Ocean Protocol Asset v4",
    "symbol": "OCEAN-A-v4",
    "owner": "0x0000000"
  }
}

Status

The status object contains attributes for marketplaces to implement various visibility states for an asset.

Attribute Type Description
state number State of the asset reflecting the NFT contract value. See State
isListed boolean If this asset should be displayed
isOrderDisabled boolean If this asset has ordering disabled

Example:

{
  "status": {
    "state": 0,
    "isListed": true,
    "isOrderDisabled": false
  }
}

Events

The events section contains information about the transactions that created or updated the DDO which can be useful for displaying a metadata history for provenance reasons.

Example:

{
  "events": [
    {
      "txid": "0x8d127de58509be5dfac600792ad24cc9164921571d168bff2f123c7f1cb4b11c",
      "blockNo": 12831214,
      "from": "0xAcca11dbeD4F863Bb3bC2336D3CE5BAC52aa1f83",
      "contract": "0x1a4b70d8c9DcA47cD6D0Fb3c52BB8634CA1C0Fdf",
      "update": false
    }
  ]
}

Statistics

The stats section contains different statistics fields.

Attribute Type Description
consumes number How often an asset was consumed, meaning how often it was either downloaded or used as part of a compute job.

Example:

{
  "stats": {
    "consumes": 4
  }
}

Full Enhanced DDO Example

{
  "@context": ["https://w3id.org/did/v1"],
  "id": "did:op:ACce67694eD2848dd683c651Dab7Af823b7dd123",
  "created": "2020-11-15T12:27:48Z",
  "updated": "2021-05-17T21:58:02Z",
  "version": "4.0.0",
  "chainId": 1,
  "metadata": {
    "description": "Sample description",
    "name": "Sample asset",
    "type": "dataset",
    "author": "OPF",
    "license": "https://market.oceanprotocol.com/terms"
  },

  // Never in response, only for publishing
  "files": [
    {
      "url": "https://demo.com/file.csv"
    }
  ],

  // Created automatically after publishing, and `files` gets removed.
  "encryptedFiles": "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",
  "services": [
    {
      "type": "access",
      "name": "Download service",
      "description": "Download service",
      "datatokenAddress": "0x123",
      "providerEndpoint": "https://myprovider.com",
      "timeout": 0
    }
  ],
  "credentials": {
    "allow": [
      {
        "type": "address",
        "values": ["0x123", "0x456"]
      }
    ],
    "deny": [
      {
        "type": "address",
        "values": ["0x2222", "0x333"]
      }
    ]
  },

  // Enhanced Aquarius response begins here
  "nft": {
    "adddress": "0x000000",
    "name": "Ocean Protocol Asset v4",
    "symbol": "OCEAN-A-v4",
    "owner": "0x0000000"
  },
  "status": {
    "state": 0,
    "isListed": true,
    "isOrderDisabled": false
  },
  "events": [
    {
      "txid": "0x8d127de58509be5dfac600792ad24cc9164921571d168bff2f123c7f1cb4b11c",
      "blockNo": 12831214,
      "from": "0xAcca11dbeD4F863Bb3bC2336D3CE5BAC52aa1f83",
      "contract": "0x1a4b70d8c9DcA47cD6D0Fb3c52BB8634CA1C0Fdf",
      "update": false,
      "chainId": 1
    }
  ],
  "stats": {
    "consumes": 4
  }
}