This page specifies metadata attributes that _must_ be included, and that _may_ be included. These attributes are organized hierarchically, from top-layer attributes like `"main"` to sub-level attributes like `"main.type"`. This page also provides DDO metadata examples.
Asset DDO metadata is stored in plaintext by default. File URLs are stored encrypted on the chain. All metadata may be encrypted, though at a severe cost to discoverability.
**This list of attributes can't be modified after creation**, because these are considered as the metadata essence of the asset created. This information is used to calculate the unique checksum of the asset. If any change would be necessary in the following attributes, it would be necessary to create a new asset derived from the existing one.
The `main` object has the following attributes. Not all are required. Some are required by only the metadata store (_remote_) and others are mandatory for _local_ metadata only. If required or not by both, they are marked with _Yes/No_ in the _Required_ column.
| **`dateCreated`** | DateTime | Yes | The date on which the asset was created by the originator. ISO 8601 format, Coordinated Universal Time, e.g. `2019-01-31T08:38:32Z`. |
| **`datePublished`** | DateTime | (remote) | The date on which the asset DDO is registered into the metadata store (Aquarius) |
| **`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". |
| **`url`** | (local) | Content URL. Omitted from the remote metadata. Supports `http(s)://` and `ipfs://` URLs. |
| **`name`** | no | File name. |
| **`index`** | yes | Index number starting from 0 of the file. |
| **`contentType`** | yes | File format. |
| **`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. |
| **`categories`** | Array of Text | No | Optional array of categories associated to the asset. |
| **`tags`** | Array of Text | No | Array of keywords or tags used to describe this content. Empty by default. |
| **`description`** | Text | No | 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. |
| **`workExample`** | Text | No | Example of the concept of this asset. This example is part of the metadata, not an external link. |
| **`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. |
| **`inLanguage`** | 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). |
| **`updateFrequency`** | An indication of update latency - i.e. How often are updates expected (seldom, annually, quarterly, etc.), or is the resource static that is never expected to get updated. |
| **`termsOfService`** | |
| **`privacy`** | |
| **`keyword`** | A list of keywords/tags describing a dataset. |
| **`structuredMarkup`** | A link to machine-readable structured markup (such as ttl/json-ld/rdf) describing the dataset. |
| **`isListed`** | Boolean | No | Use to flag unsuitable content. True by default. If it's false, the content must not be returned. |
| **`isRetired`** | Boolean | No | Flag retired content. False by default. If it's true, the content may either not be returned, or returned with a note about retirement. |
| **`isOrderDisabled`** | Boolean | No | For temporarily disabling ordering assets, e.g. when file host is in maintenance. False by default. If it's true, no ordering of assets for download or compute should be allowed. |
This is what the DDO metadata looks like with all fields in plaintext. This is before it's stored on-chain or when it's retrieved and decrypted into a local cache.
