Graph Service

This document (version 0.2) defines a graph service according to the terms set out in the core specification.

The graph service describes how entities can be created, queried, updated, and linked together – including the block entity, represented by the properties sent to the block.

Glossary

Block entity: an instance of data conforming to the block’s schema.

Entity: an instance of data, often corresponding to a thing in the world, of a particular entity type.

Entity type: a specific type of entity, with a schema defining its structure. Entities have a type, and types have a schema.

Graph: a network of entities connected by links.

Link: a connection or relation between two entities.

Linked entities: entities which are linked to the block entity, whether directly or via other entities.

Properties: the fields on a schema, what types of data are permitted as their values, and any other validation rules. Field types may be scalar (integer, string etc.), complex objects, collections (lists/arrays), or refer to another schema.

Schema: a definition of a data structure, associated with an entity type. Entities of a given type must have properties which conform to the type’s schema.

Defining blocks

Block package

Block package Summary

Blocks using the graph service may provide a schema which describes the shape of their own properties, if any. Embedding applications should use this to constrain the properties they send to blocks. These properties are part of the block entity.

The block’s schema may be included as a file in the block package, or referred to by remote address (a URL). If the block has a schema, a path to it must be added to their block-metadata.json, under a schema key.

Blocks may also add default and examples keys to block-metadata.json to define default and example properties conforming to their schema. If more complex example data is required that involves specifying other entities and links between them, which the block will make use of, a block package may also include an example-graph.json.

Block package Specification

Blocks

A block using the graph service MAY expand block-metadata.json to specify:

• schema: a path to a JSON file describing the properties the block accepts as part of the block entity, using JSON Schema vocabulary. This file may be included in the block package, or hosted at a remote address. If the schema hosted at a remote address is subject to change, bear in mind that changes in the schema may invalidate other values in the block metadata (e.g. default) or the block’s functioning (e.g. if important constraints are removed).
• default: an object, conforming to the block’s schema, representing the default data that applications should provide when creating a block, unless (a) the block can handle being provided no data when first instantiated or (b) variants is provided (see below)
• examples: an array of objects conforming to the block's schema which provide examples of the data that can be passed to it
• variants: an array of objects, each with a name and properties, and optionally description, icon, and examples. These objects represents different variants of the block that the user can create, where properties sets the starting properties. As a simple example, a ‘header’ block might have variants with the name ‘Heading 1’ and ‘Heading 2’, which start with { level: 1 } and { level: 2 } as properties, respectively

If schema is defined, the JSON schema file it refers to:

• MUST specify a required array naming any properties the block will not function without (this MAY be omitted if there are no such properties)
• SHOULD specify any further constraints or validation requirements which improve the block’s functionality
• MAY specify an additional root-level field, configProperties, which is an array of string values which MUST be present as a key on the block schema's properties, i.e. each must name a property the block expects. This field is used to indicate which properties a block considers to be part of 'configuring' how it appears or behaves, rather than data users are creating or viewing via the blocks.

If more complex example data is required, a block’s package may also include a file at the root named example-graph.json, which MUST be a JSON object, and MAY contain one or more of:

• entities
• entityTypes
• links
• linkedAggregations

If defined, each field MUST be an array of JSON objects, which MUST conform to the structure defined for each of these resources, as specified in entity definition.

Embedding applications

Embedding applications MUST use the constraints set in the block’s schema, if defined, to constrain the data it sends under properties in the block entity, assuming the embedding application implements the blockEntity message.

Embedding applications MAY choose to display their own UI to allow users to set any values on the block entity described in configProperties, and could allow users to set values for them for all blocks of a type (rather than on a per-block instance basis)

Entity definition

Structure

Structure Summary

An entity is a combination of identifying fields and properties.

The identifying fields are fixed and specified in this document, and appear as keys at the root of the entity data object.

The properties can be any JSON object which is valid for the entity’s type. This object is nested under a properties key on the entity data object.

Each entity has an entity type representing the type of thing that it is. In turn, an entity type has a schema which sets constraints on the permitted properties belonging to an entity.

Links represent connections or relations between entities. In the language of an entity graph, the links are the edges, and the entities are the nodes.

Linked aggregations represent a link from a block to a particular aggregation of entities, e.g. the top 10 entities of type Person, sorted by a particular property.

Structure Specification

Entities

When embedding applications pass entities to blocks, whether the block entity or any other:

• entities MUST be represented by an object, which contains one or more identifying fields at the top level. The object:

  • MUST contain an entityId identifying the entity, which MUST be a string.
  • MAY contain an entityTypeId identifying the entity type the entity belongs to, which MUST be a string (if defined).
• MUST contain a properties field if the block has defined any required properties in its schema, and otherwise MAY be omitted. If present, it:

  • MUST be an object
  • MUST conform to the constraints described in the entity’s schema, if any

i.e. any entity MUST conform to the following schema:

{
  "$id": "https://blockprotocol.org/types/services/graph/entity",
  "title": "Entity",
  "type": "object",
  "properties": {
    "entityId": {
      "type": "string"
    },
    "entityTypeId": {
      "type": "string"
    },
    "properties": {
      "$ref": "https://example.com/path-to-the-entity-schema"
    }
  },
  "required": ["entityId"]
}

Entity types

Embedding applications SHOULD also provide – via the entityTypes message – an entity type for each entity they provide the block, including the block entity. Where provided, an entity type:

• MUST be represented by an object, which:

  • MUST contain an entityTypeId identifying the type, which MUST be a string
  • MUST contain a schema, a JSON Schema object defining the constraints on the data in the entity’s properties field, which

    • MUST be of type: "object"
    • SHOULD use our JSON Schema extensions where appropriate
    • MAY otherwise contain any valid JSON Schema

i.e. entity types MUST conform to the following JSON schema:

{
  "$id": "https://blockprotocol.org/types/services/graph/entity-type",
  "title": "EntityType",
  "type": "object",
  "properties": {
    "entityTypeId": {
      "type": "string"
    },
    "schema": {
      "$ref": "https://json-schema.org/draft/2020-12/schema"
    }
  },
  "required": ["entityTypeId", "schema"]
}

Blocks SHOULD use any schemas provided in the entityTypes message to understand the constraints on user input for each entity (e.g. what type(s) of data are valid for each property).

Links

Entities MAY be connected by a link, which:

• MUST contain:

  • sourceEntityId: the entityId of the source entity, which MUST be a string
  • destinationEntityId: the id of a single entity the link is made to, which MUST be a string
  • path: the path to the field on the source entity this link is conceptually made on, expressed as a JSON path, which MUST be a string
• MAY contain

  • index: the position of this link in a list (for where ordering of links is important), which MUST be an integer (if defined), where 0 is the first entry in the list

i.e. links MUST conform to the following schema:

{
  "$id": "https://blockprotocol.org/types/services/graph/link",
  "title": "Link",
  "type": "object",
  "properties": {
    "sourceEntityId": {
      "type": "string"
    },
    "destinationEntityId": {
      "type": "string"
    },
    "path": {
      "type": "string"
    },
    "index": {
      "type": "integer",
      "inclusiveMinimum": 0
    }
  },
  "required": ["sourceEntityId", "destinationEntityId", "path"]
}

Where the block entity has links from it to other entities:

• Embedding applications MUST implement a blockGraph message which represents the graph with the block entity at the root, the data for which MUST be an object, which:

  • MUST contain a linkGroups key, which contains a list of objects which group the links in the resolved graph (i.e. the edges) by entity and path. Each object:

    • MUST contain links, an array of links
    • MUST contain the sourceEntityId, identical across all entries in links
    • MUST contain the path, identical across all entries in path
  • MUST contain a linkedEntities key, which contains a list of the entities in the resolved graph (i.e. the nodes)
  • MUST contain a depth key, which indicates the depth to which the graph around the block entity has been resolved.
• Embedding applications MUST at least provide the links from the block entity. This represents a depth of 0. They MAY also include the entities linked from the block entity and their links which is a depth of 1, and so on.
• See blockGraph

linkGroups should conform to the following schema:

{
  "$id": "https://blockprotocol.org/types/services/graph/link-group",
  "title": "LinkGroup",
  "type": "object",
  "properties": {
    "links": {
      "type": "array",
      "items": {
        "$ref": "https://blockprotocol.org/types/services/graph/link"
      }
    },
    "sourceEntityId": {
      "type": "string"
    },
    "path": {
      "type": "string"
    }
  },
  "required": ["sourceEntityId", "destinationEntityId", "path"]
}

Linked aggregations

Blocks may also wish to link an entity to a particular aggregation of entities. To do so, blocks SHOULD create a LinkedAggregationDefinition, which:

• MUST contain:

  • sourceEntityId: the entityId of the source entity
  • operation: an aggregation operation which the embedding application should resolve the link to, following the structure of the operation object
  • path: the path to the field on the source entity this link is conceptually made on, expressed as a JSON path, which MUST be a string

i.e. a linked aggregation definition must conform to the following schema:

{
  "$id": "https://blockprotocol.org/types/services/graph/linked-aggregation-definition",
  "title": "LinkedAggregationDefinition",
  "type": "object",
  "properties": {
    "sourceEntityId": {
      "type": "string"
    },
    "path": {
      "type": "string"
    },
    "operation": {
      "$ref": "https://blockprotocol.org/types/services/graph/aggregation-operation"
    }
  },
  "required": ["sourceEntityId", "operation", "path"]
}

Identification

Identification Summary

Blocks must pass an entityId when making requests in respect of any entity.

Embedding applications should ensure this is stable and unique for any given entity.

Identification Specification

Blocks MUST provide entityId when identifying a particular entity for the purpose of messages under the graph service.

Embedding applications MUST provide entityId for each entity it supplies the block at the root of the entity data object, as described under Structure above.

entityId SHOULD be a stable, unique reference to the entity, so that blocks may use it for comparing the identity of entities – i.e. so that blocks can assume that entities with the same entityId are the same entity, and that the same entity referenced in different places will have the same entityId wherever it appears.

JSON Schema extensions

JSON Schema extensions Summary

We define additional keywords for use as part of a JSON Schema definition.

We will publish a JSON schema vocabulary and meta-schema which allows for validating these custom keywords.

We also intend to introduce a richer vocabulary for defining entities and links between them in JSON Schema, using composable property types and data types. Please see the RFC.

JSON Schema extensions Specification

As well as the core and validation JSON Schema vocabularies:, the following keywords MAY be used at the root of the schema definition:

• labelProperty: a single string, which MUST be present as a key on the schema's properties, i.e. it must name a property available on the entity. Where an entity’s schema is provided as part of the entityTypes message, and it contains a labelProperty pointing to a defined property on the entity, blocks MUST use the value for that property as a display name for the entity where appropriate.

{
  "$id": "https://example.com/Person",
  "type": "object",
  "properties": {
    "name": { "type": "string" },
    "age": { "type": "number" }
  },
  "labelProperty": "name"
}

Messages

Error definitions

Error definitions Specification

The following error codes MAY appear as a value for code in an entry in the errors array sent with any message:

• NOT_FOUND: the message relied on an entity that was not found
• FORBIDDEN: the message relied on permissions that the user or block does not have
• INVALID_INPUT: the message relied on previous input that was missing or otherwise invalid

Individual messages MAY specify only a subset of these codes as being valid for that message.

Message definitions

Message definitions Summary

Messages under the graph service can be grouped into two functional categories:

• values provided by the embedding application, marked as source: "embedder" and sentOnInitialization: true
• requests made by the block during its lifetime, marked as source: "block"

Note that there is no reason why embedding applications cannot make requests, nor why blocks cannot send values on initialization, but the service does yet not specify any such messages.

The values are all sent from the embedding application to the block on initialization, and re-sent subsequently if they change. They are:

• blockEntity: the block entity, conforming to the constraints defined in the block schema
• entityTypes: the entity type definitions for any entities provided to the block in other messages
• blockGraph: the entity graph with the block at its root, which contains: - linkedEntities: the entities linked from the block entity, and from those entities, and so on, resolved to a depth determined by the embedding application - linkGroups: the links from the block entity and the links from any entities in linkedEntities, grouped by source entity and link path
• linkedAggregations: field containing the definitions and results of aggregations linked from the block’s entity - these are special objects which contain an aggregation definition (e.g. in plain English, "top 10 Cars sorted by age, descending") and its results at the time of provision
• readonly: whether or not the block should display in ‘readonly’ mode, disabling or hiding any editing controls it offers.

The requests may be made by the block once it has been initialized, and represent operations which create, read, update or delete entities, entity types, and create links. They are named according to the pattern [action][Resource], e.g. createEntity.

As well as the formal service JSON specification, the messages can be sent and received via the @blockprotocol/graph package.

Message definitions Specification

The messages available for exchange in the graph service are defined in the service's JSON definition and are also listed below for ease of reference.