# Using External Vocabularies

JSON-LD allows to define classes and properties of your API with open vocabularies such as Schema.org and Good Relations.

API Platform provides attributes usable on PHP classes and properties for specifying a related external IRI.

<?php
// api/src/Entity/Book.php
namespace App\Entity;

use ApiPlatform\Metadata\ApiProperty;
use ApiPlatform\Metadata\ApiResource;

#[ApiResource(types: ['https://schema.org/Book'])]
class Book
{
    // ...

    #[ApiProperty(types: ['https://schema.org/name'])]
    public $name;
    
    // ...
}

The generated JSON for products and the related context document will now use external IRIs according to the specified attributes:

GET /books/22

{
  "@context": "/contexts/Book",
  "@id": "/books/22",
  "@type": "https://schema.org/Book",
  "name": "My awesome book"
}

GET /contexts/Book

{
  "@context": {
    "@vocab": "http://example.com/apidoc#",
    "hydra": "http://www.w3.org/ns/hydra/core#",
    "name": "https://schema.org/name"
  }
}

An extended list of existing open vocabularies is available on the Linked Open Vocabularies (LOV) database.

By default, when using validations API Platform will try to define known Schema.org types as IRIs for your properties if you did not provide any in your #[ApiProperty] attributes. Built-in mapping is:

Constraints	Schema.org type
`Symfony\Component\Validator\Constraints\Url`	`https://schema.org/url`
`Symfony\Component\Validator\Constraints\Email`	`https://schema.org/email`
`Symfony\Component\Validator\Constraints\Uuid`	`https://schema.org/identifier`
`Symfony\Component\Validator\Constraints\CardScheme`	`https://schema.org/identifier`
`Symfony\Component\Validator\Constraints\Bic`	`https://schema.org/identifier`
`Symfony\Component\Validator\Constraints\Iban`	`https://schema.org/identifier`
`Symfony\Component\Validator\Constraints\Date`	`https://schema.org/Date`
`Symfony\Component\Validator\Constraints\DateTime`	`https://schema.org/DateTime`
`Symfony\Component\Validator\Constraints\Time`	`https://schema.org/Time`
`Symfony\Component\Validator\Constraints\Image`	`https://schema.org/image`
`Symfony\Component\Validator\Constraints\File`	`https://schema.org/MediaObject`
`Symfony\Component\Validator\Constraints\Currency`	`https://schema.org/priceCurrency`
`Symfony\Component\Validator\Constraints\Isbn`	`https://schema.org/isbn`
`Symfony\Component\Validator\Constraints\Issn`	`https://schema.org/issn`

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# Using External Vocabularies