Describe | @m-ld/m-ld

A simple means to get the properties of a specific subject, or a set of subjects matching some @where clause.

Examples:

Describe a specific subject whose @id is fred

{
  "@describe": "fred"
}

Describe all subjects in the domain

{
  "@describe": "?id",
  "@where": { "@id": "?id" }
}

Describe subjects with a property age of 40

{
  "@describe": "?id",
  "@where": {
    "@id": "?id",
    "age": 40
  }
}

Describe all subjects referenced by fred via any property

{
  "@describe": "?id",
  "@where": {
    "@id": "fred",
    "?prop": { "@id": "?id" }
  }
}

See the @where property for more examples of how to use a where clause.

see: json-rql describe

Hierarchy

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- Describe

Index

Properties

Optional @context

@context: Context

An optional JSON-LD Context for the query. Use of a query-specific Context is rarely required, as the context is typically the local application, whose needs are specified by the local clone configuration.

@describe

@describe: Iri | Variable | (Iri | Variable)[]

Specifies a single Variable or Iri to return. Each matched value for the identified variable will be output as a Subject with its top-level properties.

Optional @where

@where: Subject | Subject[] | Group

The data pattern to match, as a set of subjects or a group. Variables are used as placeholders to capture matching properties and values in the domain.

Examples:

Match a subject by its @id

{
  ...
  "@where": { "@id": "fred" }
}

Match a subject where any property has a given value

{
  ...
  "@where": {
    "@id": "?id",
    "?prop": "Bedrock"
  }
}

Match a subject with a given property, having any value

{
  ...
  "@where": {
    "@id": "?id",
    "name": "?name"
  }
}

The Javascript engine supports filters for subject identities, properties and values, including inline filters.

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