Data Contract#

Data Contract Overview#

Data contracts define the schema (structure) of data an application will store on Dash Platform. Contracts are described using JSON Schema which allows the platform to validate the contract-related data submitted to it.

The following sections provide details that developers need to construct valid contracts: documents and definitions. All data contracts must define one or more documents, whereas definitions are optional and may not be used for simple contracts.

General Constraints#

There are a variety of constraints currently defined for performance and security reasons. The following constraints are applicable to all aspects of data contracts. Unless otherwise noted, these constraints are defined in the platform’s JSON Schema rules (e.g. rs-dpp data contract meta schema).

Keyword#

🚧

The $ref keyword has been disabled since Platform v0.22.

Keyword

Constraint

default

Restricted - cannot be used (defined in DPP logic)

propertyNames

Restricted - cannot be used (defined in DPP logic)

uniqueItems: true

maxItems must be defined (maximum: 100000)

pattern: <something>

maxLength must be defined (maximum: 50000)

format: <something>

maxLength must be defined (maximum: 50000)

$ref: <something>

Temporarily disabled
$ref can only reference $defs -
remote references not supported

if, then, else, allOf, anyOf, oneOf, not

Disabled for data contracts

dependencies

Not supported. Use dependentRequired and dependentSchema instead

additionalItems

Not supported. Use items: false and prefixItems instead

patternProperties

Restricted - cannot be used for data contracts

pattern

Accept only RE2 compatible regular expressions (defined in DPP logic)

Data Size#

Note: These constraints are defined in the Dash Platform Protocol logic (not in JSON Schema).

All serialized data (including state transitions) is limited to a maximum size of 16 KB.

Additional Properties#

Although JSON Schema allows additional, undefined properties by default, they are not allowed in Dash Platform data contracts. Data contract validation will fail if they are not explicitly forbidden using the additionalProperties keyword anywhere properties are defined (including within document properties of type object).

Include the following at the same level as the properties keyword to ensure proper validation:

"additionalProperties": false

Data Contract Object#

The data contract object consists of the following fields as defined in the JavaScript reference client (rs-dpp):

Property

Type

Required

Description

protocolVersion

integer

Yes

The platform protocol version (currently 1)

$schema

string

Yes

A valid URL (default: https://schema.dash.org/dpp-0-4-0/meta/data-contract)

$id

array of bytes

Yes

Contract ID generated from ownerId and entropy (32 bytes; content media type: application/x.dash.dpp.identifier)

version

integer

Yes

The data contract version

ownerId

array of bytes

Yes

Identity that registered the data contract defining the document (32 bytes; content media type: application/x.dash.dpp.identifier

documents

object

Yes

Document definitions (see Documents for details)

$defs

object

No

Definitions for $ref references used in the documents object (if present, must be a non-empty object with <= 100 valid properties)

Data Contract Schema#

Details regarding the data contract object may be found in the rs-dpp data contract meta schema. A truncated version is shown below for reference:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://schema.dash.org/dpp-0-4-0/meta/data-contract",
  "type": "object",
  "$defs": {
    // Truncated ...
  },
  "properties": {
    "protocolVersion": {
      "type": "integer",
      "minimum": 0,
      "$comment": "Maximum is the latest protocol version"
    },
    "$schema": {
      "type": "string",
      "const": "https://schema.dash.org/dpp-0-4-0/meta/data-contract"
    },
    "$id": {
      "type": "array",
      "byteArray": true,
      "minItems": 32,
      "maxItems": 32,
      "contentMediaType": "application/x.dash.dpp.identifier"
    },
    "version": {
      "type": "integer",
      "minimum": 1
    },
    "ownerId": {
      "type": "array",
      "byteArray": true,
      "minItems": 32,
      "maxItems": 32,
      "contentMediaType": "application/x.dash.dpp.identifier"
    },
    "documents": {
      "type": "object",
      "propertyNames": {
        "pattern": "^[a-zA-Z0-9-_]{1,64}$"
      },
      "additionalProperties": {
        "type": "object",
        "allOf": [
          {
            "properties": {
              "indices": {
                "type": "array",
                "items": {
                  "type": "object",
                  "properties": {
                    "name": {
                      "type": "string",
                      "minLength": 1,
                      "maxLength": 32
                    },
                    "properties": {
                      "type": "array",
                      "items": {
                        "type": "object",
                        "propertyNames": {
                          "maxLength": 256
                        },
                        "additionalProperties": {
                          "type": "string",
                          "enum": [
                            "asc"
                          ]
                        },
                        "minProperties": 1,
                        "maxProperties": 1
                      },
                      "minItems": 1,
                      "maxItems": 10
                    },
                    "unique": {
                      "type": "boolean"
                    }
                  },
                  "required": [
                    "properties",
                    "name"
                  ],
                  "additionalProperties": false
                },
                "minItems": 1,
                "maxItems": 10
              },
              "type": {
                "const": "object"
              },
              "signatureSecurityLevelRequirement": {
                "type": "integer",
                "enum": [
                  0,
                  1,
                  2,
                  3
                ],
                "description": "Public key security level. 0 - Master, 1 - Critical, 2 - High, 3 - Medium. If none specified, High level is used"
              }
            }
          },
          {
            "$ref": "#/$defs/documentSchema"
          }
        ],
        "unevaluatedProperties": false
      },
      "minProperties": 1,
      "maxProperties": 100
    },
    "$defs": {
      "$ref": "#/$defs/documentProperties"
    }
  },
  "required": [
    "protocolVersion",
    "$schema",
    "$id",
    "version",
    "ownerId",
    "documents"
  ],
  "additionalProperties": false
}

Example

{
  "id": "AoDzJxWSb1gUi2dSmvFeUFpSsjZQRJaqCpn7vCLkwwJj",
  "ownerId": "7NUbPf231ixt1kVBQsBvSMMBxd7AgPad8KtdtfFGhXDP",
  "schema": "https://schema.dash.org/dpp-0-4-0/meta/data-contract",
  "documents": {
    "note": {
      "properties": {
        "message": {
          "type": "string"
        }
      },
      "additionalProperties": false
    }
  }
}

Data Contract id#

The data contract $id is a hash of the ownerId and entropy as shown here.

// From the Rust reference implementation (rs-dpp)
// generate_data_contract.rs
/// Generate data contract id based on owner id and entropy
pub fn generate_data_contract_id(owner_id: impl AsRef<[u8]>, entropy: impl AsRef<[u8]>) -> Vec<u8> {
    let mut b: Vec<u8> = vec![];
    let _ = b.write(owner_id.as_ref());
    let _ = b.write(entropy.as_ref());
    hash(b)
}

Data Contract version#

The data contract version is an integer representing the current version of the contract. This
property must be incremented if the contract is updated.

Data Contract Documents#

The documents object defines each type of document required by the data contract. At a minimum, a document must consist of 1 or more properties. Documents may also define indices and a list of required properties. The additionalProperties properties keyword must be included as described in the constraints section.

The following example shows a minimal documents object defining a single document (note) that has one property (message).

{
  "note": {
    "type": "object",
    "properties": {
      "message": {
        "type": "string",
        "position": 0
      }
    },
    "additionalProperties": false
  }
}

Document Properties#

The properties object defines each field that will be used by a document. Each field consists of an object that, at a minimum, must define its data type (string, number, integer, boolean, array, object). Fields may also apply a variety of optional JSON Schema constraints related to the format, range, length, etc. of the data.

Note: The object type is required to have properties defined either directly or via the data contract’s $defs. For example, the body property shown below is an object containing a single string property (objectProperty):

const contractDocuments = {
  message: {
    "type": "object",
    properties: {
      body: {
        type: "object",
        properties: {
          objectProperty: {
            type: "string",
            position: 0
          },
        },
        additionalProperties: false,
      },
      header: {
        type: "string",
        position: 1
      }
    },
    additionalProperties: false
  }
};

Note: A full explanation of the capabilities of JSON Schema is beyond the scope of this document. For more information regarding its data types and the constraints that can be applied, please refer to the JSON Schema reference documentation.

Property Constraints#

There are a variety of constraints currently defined for performance and security reasons.

Description

Value

Minimum number of properties

1

Maximum number of properties

100

Minimum property name length

1 (Note: minimum length was 3 prior to v0.23)

Maximum property name length

64

Property name characters

Alphanumeric (A-Z, a-z, 0-9)
Hyphen (-)
Underscore (_)

Prior to Dash Platform v0.23 there were stricter limitations on minimum property name length and the characters that could be used in property names.

Required Properties (Optional)#

Each document may have some fields that are required for the document to be valid and other fields that are optional. Required fields are defined via the required array which consists of a list of the field names from the document that must be present. The required object should be excluded for documents without any required properties.

"required": [
  "<field name a>",
  "<field name b>"
]

Example
The following example (excerpt from the DPNS contract’s domain document) demonstrates a document that has 6 required fields:

"required": [
  "label",
  "normalizedLabel",
  "normalizedParentDomainName",
  "preorderSalt",
  "records",
  "subdomainRules"
]

Document Indices#

Document indices may be defined if indexing on document fields is required.

Note: Dash Platform v0.23 only allows ascending default ordering for indices.

The indices array consists of:

  • One or more objects that each contain:

    • A unique name for the index

    • A properties array composed of a <field name: sort order> object for each document field that is part of the index (sort order: asc only for Dash Platform v0.23)

    • An (optional) unique element that determines if duplicate values are allowed for the document type

Note:

  • The indices object should be excluded for documents that do not require indices.

  • When defining an index with multiple properties (i.e a compound index), the order in which the properties are listed is important. Refer to the mongoDB documentation for details regarding the significance of the order as it relates to querying capabilities. Dash uses GroveDB which works similarly but does requiring listing all the index’s fields in query order by statements.

"indices": [
  {
    "name": "Index1",
    "properties": [
      { "<field name a>": "asc" },
      { "<field name b>": "asc" }
    ],
    "unique": true|false
  },
  {
    "name": "Index2",
    "properties": [
      { "<field name c>": "asc" },
    ],
  }
]
Index Constraints#

For performance and security reasons, indices have the following constraints. These constraints are subject to change over time.

Description

Value

Minimum/maximum length of index name

1 / 32

Maximum number of indices

10

Maximum number of unique indices

3

Maximum number of properties in a single index

10

Maximum length of indexed string property

63

Note: Dash Platform v0.22+. does not allow indices for arrays
Maximum length of indexed byte array property

255

Note: Dash Platform v0.22+. does not allow indices for arrays
Maximum number of indexed array items

1024

Usage of $id in an index disallowed

N/A

Example
The following example (excerpt from the DPNS contract’s preorder document) creates an index named saltedHash on the saltedDomainHash property that also enforces uniqueness across all documents of that type:

"indices": [
  {
    "name": "saltedHash",
    "properties": [
      {
        "saltedDomainHash": "asc"
      }
    ],
    "unique": true
  }
]

Full Document Syntax#

This example syntax shows the structure of a documents object that defines two documents, an index, and a required field.

{
  "<document name a>": {
    "type": "object",
    "properties": {
      "<field name b>": {
        "type": "<field data type>",
        "position": "<number>"
      },
      "<field name c>": {
        "type": "<field data type>",
        "position": "<number>"
      },
    },
    "indices": [
      {
        "name": "<index name>",
        "properties": [
          {
            "<field name c>": "asc"
          }
        ],
        "unique": true|false
      },
    ],
    "required": [
      "<field name c>"
    ]
    "additionalProperties": false
  },
  "<document name x>": {
    "type": "object",
    "properties": {
      "<property name y>": {
        "type": "<property data type>",
        "position": "<number>"
      },
      "<property name z>": {
        "type": "<property data type>",
        "position": "<number>"
      },
    },
    "additionalProperties": false
  },    
}

Document Schema#

Full document schema details may be found in this section of the rs-dpp data contract meta schema.

Data Contract Definitions#

❗️ Definitions are currently unavailable

The optional $defs object enables definition of aspects of a schema that are used in multiple places. This is done using the JSON Schema support for reuse. Items defined in $defs may then be referenced when defining documents through use of the $ref keyword.

Note:

  • Properties defined in the $defs object must meet the same criteria as those defined in the documents object (e.g. the additionalProperties properties keyword must be included as described in the constraints section).

  • Data contracts can only use the $ref keyword to reference their own $defs. Referencing external definitions is not supported by the platform protocol.

Example
The following example shows a definition for a message object consisting of two properties:

{
  // Preceding content truncated ...
  "$defs": {
    "message": {
      "type": "object",
      "properties": {
        "timestamp": {
          "type": "number"
        },
        "description": {
          "type": "string"
        }
      },
      "additionalProperties": false
    }
  }
}

Data Contract State Transition Details#

There are two data contract-related state transitions: data contract create and data contract update. Details are provided in this section.

Data Contract Creation#

Data contracts are created on the platform by submitting the data contract object in a data contract create state transition consisting of:

Field

Type

Description

protocolVersion

integer

The platform protocol version (currently 1)

type

integer

State transition type (0 for data contract create)

dataContract

data contract object

Object containing the data contract details

entropy

array of bytes

Entropy used to generate the data contract ID. Generated as shown here. (32 bytes)

signaturePublicKeyId

number

The id of the identity public key that signed the state transition

signature

array of bytes

Signature of state transition data (65 or 96 bytes)

Each data contract state transition must comply with this JSON-Schema definition established in rs-dpp:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "properties": {
    "protocolVersion": {
      "type": "integer",
      "$comment": "Maximum is the latest protocol version"
    },
    "type": {
      "type": "integer",
      "const": 0
    },
    "dataContract": {
      "type": "object"
    },
    "entropy": {
      "type": "array",
      "byteArray": true,
      "minItems": 32,
      "maxItems": 32
    },
    "signaturePublicKeyId": {
      "type": "integer",
      "minimum": 0
    },
    "signature": {
      "type": "array",
      "byteArray": true,
      "minItems": 65,
      "maxItems": 96
    }
  },
  "additionalProperties": false,
  "required": [
    "protocolVersion",
    "type",
    "dataContract",
    "entropy",
    "signaturePublicKeyId",
    "signature"
  ]
}

Example State Transition

{
  "protocolVersion":1,
  "type":0,
  "signature":"IFmEb/OwyYG0yn33U4/kieH4JL63Ft25GAun+XqWOalkbDrpL9z+OH+Sb03xsyMNzoILC2T1Q8yV1q7kCmr0HuQ=",
  "signaturePublicKeyId":0,
  "dataContract":{
    "protocolVersion":1,
    "$id":"44dvUnSdVtvPPeVy6mS4vRzJ4zfABCt33VvqTWMM8VG6",
    "$schema":"https://schema.dash.org/dpp-0-4-0/meta/data-contract",
    "version":1,
    "ownerId":"6YfP6tT9AK8HPVXMK7CQrhpc8VMg7frjEnXinSPvUmZC",
    "documents":{
      "note":{
        "type":"object",
        "properties":{
          "message":{
            "type":"string"
          }
        },
        "additionalProperties":false
      }
    }
  },
  "entropy":"J2Sl/Ka9T1paYUv6f2ec5MzaaACs9lcUvOskBU0SMlo="
}

Data Contract Update#

Existing data contracts can be updated in certain backwards-compatible ways. The following aspects
of a data contract can be updated:

  • Adding a new document

  • Adding a new optional property to an existing document

  • Adding non-unique indices for properties added in the update

Data contracts are updated on the platform by submitting the modified data contract
object in a data contract update state transition consisting of:

Field

Type

Description

protocolVersion

integer

The platform protocol version (currently 1)

type

integer

State transition type (4 for data contract update)

dataContract

data contract object

Object containing the updated data contract details
Note: the data contract’s version property must be incremented with each update

signaturePublicKeyId

number

The id of the identity public key that signed the state transition

signature

array of bytes

Signature of state transition data (65 or 96 bytes)

Each data contract state transition must comply with this JSON-Schema definition established in
rs-dpp:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "properties": {
    "protocolVersion": {
      "type": "integer",
      "$comment": "Maximum is the latest protocol version"
    },
    "type": {
      "type": "integer",
      "const": 4
    },
    "dataContract": {
      "type": "object"
    },
    "signaturePublicKeyId": {
      "type": "integer",
      "minimum": 0
    },
    "signature": {
      "type": "array",
      "byteArray": true,
      "minItems": 65,
      "maxItems": 96
    }
  },
  "additionalProperties": false,
  "required": [
    "protocolVersion",
    "type",
    "dataContract",
    "signaturePublicKeyId",
    "signature"
  ]
}

Example State Transition

{
  "protocolVersion":1,
  "type":4,
  "signature":"IBboAbqbGBiWzyJDyhwzs1GujR6Gb4m5Gt/QCugLV2EYcsBaQKTM/Stq7iyIm2YyqkV8VlWqOfGebW2w5Pjnfak=",
  "signaturePublicKeyId":0,
  "dataContract":{
    "protocolVersion":1,
    "$id":"44dvUnSdVtvPPeVy6mS4vRzJ4zfABCt33VvqTWMM8VG6",
    "$schema":"https://schema.dash.org/dpp-0-4-0/meta/data-contract",
    "version":2,
    "ownerId":"6YfP6tT9AK8HPVXMK7CQrhpc8VMg7frjEnXinSPvUmZC",
    "documents":{
      "note":{
        "type":"object",
        "properties":{
          "message":{
            "type":"string"
          },
          "author":{
            "type":"string"
          }
        },
        "additionalProperties":false
      }
    }
  }
}

Data Contract State Transition Signing#

Data contract state transitions must be signed by a private key associated with the contract owner’s identity.

The process to sign a data contract state transition consists of the following steps:

  1. Canonical CBOR encode the state transition data - this include all ST fields except the signature and signaturePublicKeyId

  2. Sign the encoded data with a private key associated with the ownerId

  3. Set the state transition signature to the value of the signature created in the previous step

  4. Set the state transitionsignaturePublicKeyId to the public key id corresponding to the key used to sign