<table><thead><tr><thwidth="169.6737288135593">Attribute</th><thwidth="164">Type</th><th>Description</th></tr></thead><tbody><tr><td><strong><code>@context</code></strong></td><td>Array of <code>string</code></td><td>Contexts used for validation.</td></tr><tr><td><strong><code>id</code></strong></td><td><code>string</code></td><td>Computed as <code>sha256(address of ERC721 contract + chainId)</code>.</td></tr><tr><td><strong><code>version</code></strong></td><td><code>string</code></td><td>Version information in <ahref="https://semver.org">SemVer</a> notation referring to this DDO spec version, like <code>4.1.0</code>.</td></tr><tr><td><strong><code>chainId</code></strong></td><td><code>number</code></td><td>Stores the chainId of the network the DDO was published to.</td></tr><tr><td><strong><code>nftAddress</code></strong></td><td><code>string</code></td><td>NFT contract linked to this asset</td></tr><tr><td><strong><code>metadata</code></strong></td><td><ahref="ddo-specification.md#metadata">Metadata</a></td><td>Stores an object describing the asset.</td></tr><tr><td><strong><code>services</code></strong></td><td><ahref="ddo-specification.md#services">Services</a></td><td>Stores an array of services defining access to the asset.</td></tr><tr><td><strong><code>credentials</code></strong></td><td><ahref="ddo-specification.md#credentials">Credentials</a></td><td>Describes the credentials needed to access a dataset in addition to the <code>services</code> definition.</td></tr></tbody></table>
<table><thead><tr><thwidth="260.3333333333333">Attribute</th><thwidth="166">Type</th><th>Description</th></tr></thead><tbody><tr><td><strong><code>created</code></strong></td><td><code>ISO date/time string</code></td><td>Contains the date of the creation of the dataset content in ISO 8601 format preferably with timezone designators, e.g. <code>2000-10-31T01:30:00Z</code>.</td></tr><tr><td><strong><code>updated</code></strong></td><td><code>ISO date/time string</code></td><td>Contains the date of last update of the dataset content in ISO 8601 format preferably with timezone designators, e.g. <code>2000-10-31T01:30:00Z</code>.</td></tr><tr><td><strong><code>description</code></strong>*</td><td><code>string</code></td><td>Details of what the resource is. For a dataset, this attribute explains what the data represents and what it can be used for.</td></tr><tr><td><strong><code>copyrightHolder</code></strong></td><td><code>string</code></td><td>The party holding the legal copyright. Empty by default.</td></tr><tr><td><strong><code>name</code></strong>*</td><td><code>string</code></td><td>Descriptive name or title of the asset.</td></tr><tr><td><strong><code>type</code></strong>*</td><td><code>string</code></td><td>Asset type. Includes <code>"dataset"</code> (e.g. csv file), <code>"algorithm"</code> (e.g. Python script). Each type needs a different subset of metadata attributes.</td></tr><tr><td><strong><code>author</code></strong>*</td><td><code>string</code></td><td>Name of the entity generating this data (e.g. Tfl, Disney Corp, etc.).</td></tr><tr><td><strong><code>license</code></strong>*</td><td><code>string</code></td><td>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".</td></tr><tr><td><strong><code>links</code></strong></td><td>Array of <code>string</code></td><td>Mapping of URL strings for data samples, or links to find out more information. Links may be to either a URL or another asset.</td></tr><tr><td><strong><code>contentLanguage</code></strong></td><td><code>string</code></td><td>The language of the content. Use one of the language codes from the <ahref="https://tools.ietf.org/html/bcp47">IETF BCP 47 standard</a></td></tr><tr><td><strong><code>tags</code></strong></td><td>Array of <code>string</code></td><td>Array of keywords or tags used to describe this content. Empty by default.</td></tr><tr><td><strong><code>categories</code></strong></td><td>Array of <code>string</code></td><td>Array of categories associated to the asset. Note: recommended to use <code>tags</code> instead of this.</td></tr><tr><td><strong><code>additionalInformation</code></strong></td><td>Object</td><td>Stores additional information, this is customizable by publisher</td></tr><tr><td><strong><code>algorithm</code></strong>**</td><td><ahref="compute-to-data/compute-to-data-algorithms.md#algorithm-metadata">Algorithm Metadata</a></td><td>Information about asset of <code>type</code><code>algorithm</code></td></tr></tbody></table>
<table><thead><tr><thwidth="259.3333333333333">Attribute</th><thwidth="121">Type</th><th>Description</th></tr></thead><tbody><tr><td><strong><code>id</code></strong>*</td><td><code>string</code></td><td>Unique ID</td></tr><tr><td><strong><code>type</code></strong>*</td><td><code>string</code></td><td>Type of service <code>access</code>, <code>compute</code>, <code>wss</code> etc.</td></tr><tr><td><strong><code>name</code></strong></td><td><code>string</code></td><td>Service friendly name</td></tr><tr><td><strong><code>description</code></strong></td><td><code>string</code></td><td>Service description</td></tr><tr><td><strong><code>datatokenAddress</code></strong>*</td><td><code>string</code></td><td>Datatoken</td></tr><tr><td><strong><code>serviceEndpoint</code></strong>*</td><td><code>string</code></td><td>Provider URL (schema + host)</td></tr><tr><td><strong><code>files</code></strong>*</td><td><ahref="#files">Files</a></td><td>Encrypted file.</td></tr><tr><td><strong><code>timeout</code></strong>*</td><td><code>number</code></td><td>Describing how long the service can be used after consumption is initiated. A timeout of <code>0</code> represents no time limit. Expressed in seconds.</td></tr><tr><td><strong><code>compute</code></strong>**</td><td><ahref="compute-to-data/compute-options.md">Compute</a></td><td>If service is of <code>type</code><code>compute</code>, holds information about the compute-related privacy settings & resources.</td></tr><tr><td><strong><code>consumerParameters</code></strong></td><td><ahref="compute-to-data/compute-options.md#consumer-parameters">Consumer Parameters</a></td><td>An object the defines required consumer input before consuming the asset</td></tr><tr><td><strong><code>additionalInformation</code></strong></td><td>Object</td><td>Stores additional information, this is customizable by publisher</td></tr></tbody></table>
By default, a consumer can access a resource if they have 1 datatoken. _Credentials_ allow the publisher to optionally specify more fine-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 datatoken _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 identification 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](https://www.w3.org/TR/vc-data-model/) and more.
In order to ensure the integrity of the DDO, a checksum is computed for each DDO:
```js
const checksum = sha256(JSON.stringify(ddo));
```
The checksum hash is used when publishing/updating metadata using the `setMetaData` function in the ERC721 contract, and is stored in the event generated by the ERC721 contract.
<details>
<summary>MetadataCreated and MetadataUpdated smart contract events</summary>
```solidity
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
);
```
</details>
_Aquarius_ should always verify the checksum after data is decrypted via a _Provider_ API call.
#### State
Each asset has a state, which is held by the NFT contract. The possible states are:
<table><thead><tr><thwidth="95">State</th><thwidth="271">Description</th><thwidth="155">Discoverable in Ocean Market</th><th>Ordering allowed</th><th>Listed under profile</th></tr></thead><tbody><tr><td><strong><code>0</code></strong></td><td>Active</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td><strong><code>1</code></strong></td><td>End-of-life</td><td>No</td><td>No</td><td>No</td></tr><tr><td><strong><code>2</code></strong></td><td>Deprecated (by another asset)</td><td>No</td><td>No</td><td>No</td></tr><tr><td><strong><code>3</code></strong></td><td>Revoked by publisher</td><td>No</td><td>No</td><td>No</td></tr><tr><td><strong><code>4</code></strong></td><td>Ordering is temporary disabled</td><td>Yes</td><td>No</td><td>Yes</td></tr><tr><td><strong><code>5</code></strong></td><td>Asset unlisted.</td><td>No</td><td>Yes</td><td>Yes</td></tr></tbody></table>
The following fields are added by _Aquarius_ in its DDO response for convenience reasons, where an asset returned by _Aquarius_ inherits the DDO fields stored on-chain.
<table><thead><tr><thwidth="144.70989551321452">Attribute</th><thwidth="234.33333333333331">Type</th><th>Description</th></tr></thead><tbody><tr><td><strong><code>address</code></strong></td><td><code>string</code></td><td>Contract address of the deployed ERC721 NFT contract.</td></tr><tr><td><strong><code>name</code></strong></td><td><code>string</code></td><td>Name of NFT set in contract.</td></tr><tr><td><strong><code>symbol</code></strong></td><td><code>string</code></td><td>Symbol of NFT set in contract.</td></tr><tr><td><strong><code>owner</code></strong></td><td><code>string</code></td><td>ETH account address of the NFT owner.</td></tr><tr><td><strong><code>state</code></strong></td><td><code>number</code></td><td>State of the asset reflecting the NFT contract value. See <ahref="ddo-specification.md#state">State</a></td></tr><tr><td><strong><code>created</code></strong></td><td><code>ISO date/time string</code></td><td>Contains the date of NFT creation.</td></tr><tr><td><strong><code>tokenURI</code></strong></td><td><code>string</code></td><td>tokenURI</td></tr></tbody></table>
<table><thead><tr><thwidth="160.77255871446232">Attribute</th><thwidth="128.33333333333331">Type</th><th>Description</th></tr></thead><tbody><tr><td><strong><code>address</code></strong></td><td><code>string</code></td><td>Contract address of the deployed ERC20 contract.</td></tr><tr><td><strong><code>name</code></strong></td><td><code>string</code></td><td>Name of NFT set in contract.</td></tr><tr><td><strong><code>symbol</code></strong></td><td><code>string</code></td><td>Symbol of NFT set in contract.</td></tr><tr><td><strong><code>serviceId</code></strong></td><td><code>string</code></td><td>ID of the service the datatoken is attached to.</td></tr></tbody></table>
Contains information about an asset's purgatory status defined in [`list-purgatory`](https://github.com/oceanprotocol/list-purgatory). Marketplace interfaces are encouraged to prevent certain user actions like adding liquidity on assets in purgatory.
<table><thead><tr><thwidth="145.92125984251967">Attribute</th><thwidth="134">Type</th><th>Description</th></tr></thead><tbody><tr><td><strong><code>state</code></strong></td><td><code>boolean</code></td><td>If <code>true</code>, asset is in purgatory.</td></tr><tr><td><strong><code>reason</code></strong></td><td><code>string</code></td><td>If asset is in purgatory, contains the reason for being there as defined in <code>list-purgatory</code>.</td></tr></tbody></table>
<table><thead><tr><thwidth="142.75440658049354">Attribute</th><thwidth="125">Type</th><th>Description</th></tr></thead><tbody><tr><td><strong><code>orders</code></strong></td><td><code>number</code></td><td>How often an asset was ordered, meaning how often it was either downloaded or used as part of a compute job.</td></tr></tbody></table>
For algorithms and datasets that are used for compute to data, there are additional fields and objects within the DDO structure that you need to consider. These include:
