Decentralized identifiers (DIDs) are a new type of identifier that enables verifiable, decentralized digital identity. Each DID is associated with a unique entity. DIDs may represent humans, objects, and more.
- 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.
- The DDO can only can be modified by _owners_ or _delegated users_.
- There _must_ be at least one client library acting as _resolver_, to get a DDO from a DID.
- A metadata cache like Aquarius can help in reading and searching through DDO data from the chain.
## Flow for publishing / retrieving DDOs
- The DDO is stored on-chain.
- It's stored encrypted (using the private key of the provider). To resolve it, you must query the provider and you will might get the clear text ddo (depends on access rights, state, etc)
| **`description`** | Text | **Yes** | Details of what the resource is. For a dataset, this attribute explains what the data represents and what it can be used for.|
| **`copyrightHolder`** | Text | No | The party holding the legal copyright. Empty by default.
| **`name`** | Text |**Yes** | Descriptive name or title of the asset. |
| **`type`** | Text |**Yes** | Asset type. Includes `"dataset"` (e.g. csv file), `"algorithm"` (e.g. Python script). Each type needs a different subset of metadata attributes. |
| **`author`** | Text |**Yes** | Name of the entity generating this data (e.g. Tfl, Disney Corp, etc.). |
| **`license`** | Text |**Yes** | 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 Link | No | Mapping of links for data samples, or links to find out more information. Links may be to either a URL or another Asset. We expect marketplaces to converge on agreements of typical formats for linked data: The Ocean Protocol itself does not mandate any specific formats as these requirements are likely to be domain-specific. The links array can be an empty array, but if there is a link object in it, then an "url" is required in that link object. |
| **`contentLanguage`** | Text | No | The language of the content. Please use one of the language codes from the [IETF BCP 47 standard](https://tools.ietf.org/html/bcp47)|
| **`type`** | Text | **Yes** | Type of service (access, compute, wss, etc |
| **`name`** | Text | No | Service friendly name |
| **`description`** | Text | No | Service description |
| **`datatokenAddress`** | Text | Yes | Datatoken address |
| **`providerEndpoint`** | Text | **Yes** | Provider URI |
| **`timeout`** | Number | **Yes** | describing how long the sevice can be used after consumption is initiated. A timeout of 0 represents no time limit. Expressed in seconds.|
| **`files`** | Array of files object |**No ** | Array of `File` objects including the encrypted file urls that overwrites the root files object for this service [Files](#files) |
| **`allowRawAlgorithm`** | `boolean` | yes | If True, a drag & drop algo can be runned |
| **`allowNetworkAccess`** | `boolean` | yes | If True, the algo job will have network access (stil WIP) |
| **`publisherTrustedAlgorithmPublishers `** | Array of `String` | yes | If Empty , then any published algo is allowed. Otherwise, only published algorithms by some publishers are allowed |
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).
| **`url`** | Local | Content URL. Omitted from the remote metadata. Supports `http(s)://` and `ipfs://` URLs. |
| **`name`** | No | File name. |
| **`checksum`** | No | Checksum of the file using your preferred format (i.e. MD5). Format specified in `checksumType`. If it's not provided can't be validated if the file was not modified after registering. |
| **`checksumType`** | No | Format of the provided checksum. Can vary according to server (i.e Amazon vs. Azure) |
| **`contentLength`** | No | Size of the file in bytes. |
| **`encoding`** | No | File encoding (e.g. UTF-8). |
| **`compression`** | No | File compression (e.g. no, gzip, bzip2, etc). |
| **`encrypted`** | No | Boolean. Is the file encrypted? If is not set is assumed the file is not encrypted |
| **`encryptionMode`** | No | Encryption mode used. Just valid if `encrypted=true` |
| **`resourceId`** | No | Remote identifier of the file in the external provider. It is typically the remote id in the cloud provider. |
| **`attributes`** | No | Key-Value hash map with additional attributes describing the asset file. It could include details like the Amazon S3 bucket, region, etc.
