---
schema_version: "1"
id: 95e9f881d3c656be7f9c8efc5083bd6f6198a92f47b670e27b1224a120d23e37
title: Schema Definition Support
collection: admin
version: current
locale: en-us
portal_url: https://docs.salesforce.com/admin/current/en-us/platform/264-0-0/external_services_intro_schema_definitions.md
canonical_url: https://help.salesforce.com/s/articleView?id=platform.external_services_intro_schema_definitions.htm&release=264.0.0&type=5
source_site: help.salesforce.com
content_type: documentation
content_hash: 8fef2c8e42178601e450225a7d189b98454047e114454763d9f40881b24131df
description: Learn about External Services' schema limits and other considerations.
products:
  - Salesforce Platform
  - Security
release: "264"
---
# Schema Definition Support

Learn about External Services' schema limits and other considerations.

### Required Editions

<table class="slds-table slds-table_bordered slds-max-medium-table_stacked slds-m-bottom_small edition"><colgroup><col></colgroup><tbody><tr class=""><td class="slds-cell-wrap" style="vertical-align:top;">Available in: Lightning Experience</td></tr><tr class=""><td class="slds-cell-wrap" style="vertical-align:top;">Available in: <strong>Enterprise</strong>, <strong>Performance</strong>, <strong>Unlimited</strong>, and <strong>Developer</strong> Editions</td></tr></tbody></table>

- **[System Limits](https://help.salesforce.com/s/articleView?id=platform.external_services_schema_def_limits.htm&release=264.0.0&type=5)**  
    External Services maximum system limits for registrations, schema size, operations, objects, properties, and file size.
- **[Callouts and Callbacks: Limits and Usage](https://help.salesforce.com/s/articleView?id=platform.external_services_schema_def_usage_considerations.htm&release=264.0.0&type=5)**  
    Limits and best approaches for callbacks and callouts to and from External Services.
- **[Schema Definitions](https://help.salesforce.com/s/articleView?id=platform.external_services_schema_def_definition.htm&release=264.0.0&type=5)**  
    Learn the basics about External Service's schema support, schema components that are ignored, and supported data types.
- **[Character Set Encodings](https://help.salesforce.com/s/articleView?id=platform.external_services_schema_def_character_set_encodings.htm&release=264.0.0&type=5)**  
    Learn about request and response character set encodings.
- **[Media Type Directives and Mapping](https://help.salesforce.com/s/articleView?id=platform.external_services_schema_def_media_type_schema_directives.htm&release=264.0.0&type=5)**  
    Learn about OpenApi 2.0 `consumes`/`produces` or OpenAPI 3.0 `content` media type schema directives.
- **[Naming and Description Conventions](https://help.salesforce.com/s/articleView?id=platform.external_services_schema_def_naming_description.htm&release=264.0.0&type=5)**  
    Learn about support for component names and descriptions defined in your schema.
- **[Defaults and Default Values](https://help.salesforce.com/s/articleView?id=platform.external_services_schema_apex_defaults.htm&release=264.0.0&type=5)**  
    Learn about External Services' support for defaults. For OpenAPI 2.0, default values set on `properties` are used. For OpenAPI 3.0 schemas, the "outermost" default is used. Non-supported configurations are ignored.
- **[Operation Output Parameters](https://help.salesforce.com/s/articleView?id=platform.external_services_schema_def_operation_output_params.htm&release=264.0.0&type=5)**  
    Learn about how External Services interprets an operation's output parameters.
- **[Structure Data Using properties and additionalProperties](https://help.salesforce.com/s/articleView?id=platform.external_services_schema_def_properties_additional_properties.htm&release=264.0.0&type=5)**  
    In an Open API specification, the properties keyword defines one or more properties on an object including the property name and data type. The additionalProperties keyword gives you the flexibility to add additional properties with an undefined schema. The named properties are accessible as Apex properties with a matching data type. The additionalProperties in the spec are accessible in Apex as a Map property.
- **[Apex Class Names and Developer Names](https://help.salesforce.com/s/articleView?id=platform.external_services_schema_def_apex_class_names.htm&release=264.0.0&type=5)**  
    Learn how External Services derives Apex class names from your schema.
- **[Apex Reserved Keywords](https://help.salesforce.com/s/articleView?id=platform.external_services_schema_def_apex_reserved_keywords.htm&release=264.0.0&type=5)**  
    Learn about External Service's support for Apex reserved keywords.
- **[Null Values](https://help.salesforce.com/s/articleView?id=platform.external_services_schema_def_null_values.htm&release=264.0.0&type=5)**  
    Learn null values are interpreted by External Services.