REST Resource Naming Guide

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In REST, primary data representation is called Resource. Having a strong and consistent REST resource naming strategy – will definitely prove one of the best design decisions in the long term.

The key abstraction of information in REST is a resource. Any information that can be named can be a resource: a document or image, a temporal service (e.g. today’s weather in Los Angeles), a collection of other resources, a non-virtual object (e.g., a person), and so on. In other words, any concept that might be the target of an author’s hypertext reference must fit within the definition of a resource. A resource is a conceptual mapping to a set of entities, not the entity that corresponds to the mapping at any particular point in time.
Roy Fielding’s dissertation

A resource can be a singleton or a collection. For example, customers is a collection resource and customer is a singleton resource (in a banking domain). We can identify customers collection resource using the URI /customers. We can identify a single customer resource using the URI /customers/{customerId}.

A resource may contain sub-collection resources also. For example, sub-collection resource accounts of a particular customer can be identified using the URN /customers/{customerId}/accounts (in a banking domain). Similarly, a singleton resource account inside the sub-collection resource accounts can be identified as follows: /customers/{customerId}/accounts/{accountId}.

REST APIs use Uniform Resource Identifiers (URIs) to address resources. REST API designers should create URIs that convey a REST API’s resource model to its potential client developers. When resources are named well, an API is intuitive and easy to use. If done poorly, that same API can feel difficult to use and understand.

The constraint of uniform interface is partially addressed by the combination of URIs and HTTP verbs and using them in line with the standards and conventions.

Below are a few tips to get you going when creating the resource URIs for your new API.

REST Resource Naming Best Practices

Use nouns to represent resources

RESTful URI should refer to a resource that is a thing (noun) instead of referring to an action (verb) because nouns have properties which verbs do not have – similar to resources have attributes. Some examples of a resource are:

• Users of the system
• User Accounts
• Network Devices etc.

and their resource URIs can be designed as below:

http://api.example.com/device-management/managed-devices
http://api.example.com/device-management/managed-devices/{device-id}
http://api.example.com/user-management/users/
http://api.example.com/user-management/users/{id}

For more clarity, let’s divide the resource archetypes into four categories (document, collection, store and controller) and then you should always target to put a resource into one archetype and then use it’s naming convention consistently. For uniformity’s sake, resist the temptation to design resources that are hybrids of more than one archetype.

1. document

   A document resource is a singular concept that is akin to an object instance or database record. In REST, you can view it as a single resource inside resource collection. A document’s state representation typically includes both fields with values and links to other related resources.

   Use singular name to denote document resource archetype.

   http://api.example.com/device-management/managed-devices/{device-id}
   http://api.example.com/user-management/users/{id}
   http://api.example.com/user-management/users/admin

2. collection

   A collection resource is a server-managed directory of resources. Clients may propose new resources to be added to a collection. However, it is up to the collection to choose to create a new resource or not. A collection resource chooses what it wants to contain and also decides the URIs of each contained resource.

   Use plural name to denote collection resource archetype.

   http://api.example.com/device-management/managed-devices
   http://api.example.com/user-management/users
   http://api.example.com/user-management/users/{id}/accounts

3. store

   A store is a client-managed resource repository. A store resource lets an API client put resources in, get them back out, and decide when to delete them. A store never generates new URIs. Instead, each stored resource has a URI that was chosen by a client when it was initially put into the store.

   Use plural name to denote store resource archetype.

   http://api.example.com/song-management/users/{id}/playlists

4. controller

   A controller resource models a procedural concept. Controller resources are like executable functions, with parameters and return values; inputs and outputs.

   Use verb to denote controller archetype.

   http://api.example.com/cart-management/users/{id}/cart/checkout
   http://api.example.com/song-management/users/{id}/playlist/play

Consistency is the key

Use consistent resource naming conventions and URI formatting for minimum ambiguily and maximum readability and maintainability. You may implement below design hints to achieve consistency:

1. Use forward slash (/) to indicate hierarchical relationships

   The forward slash (/) character is used in the path portion of the URI to indicate a hierarchical relationship between resources. e.g.

   http://api.example.com/device-management
   http://api.example.com/device-management/managed-devices
   http://api.example.com/device-management/managed-devices/{id}
   http://api.example.com/device-management/managed-devices/{id}/scripts
   http://api.example.com/device-management/managed-devices/{id}/scripts/{id}

2. Do not use trailing forward slash (/) in URIs

   As the last character within a URI’s path, a forward slash (/) adds no semantic value and may cause confusion. It’s better to drop them completely.

   http://api.example.com/device-management/managed-devices/
   http://api.example.com/device-management/managed-devices  /*This is much better version*/

3. Use hyphens (-) to improve the readability of URIs

   To make your URIs easy for people to scan and interpret, use the hyphen (-) character to improve the readability of names in long path segments.

   http://api.example.com/inventory-management/managed-entities/{id}/install-script-location  //More readable
   http://api.example.com/inventory-management/managedEntities/{id}/installScriptLocation  //Less readable

4. Do not use underscores ( _ )

   It’s possible to use an underscore in place of a hyphen to be used as separator – But depending on the application’s font, it’s possible that the underscore (_) character can either get partially obscured or completely hidden in some browsers or screens.

   To avoid this confusion, use hyphens (-) instead of underscores ( _ ).

   http://api.example.com/inventory-management/managed-entities/{id}/install-script-location  //More readable
   http://api.example.com/inventory_management/managed_entities/{id}/install_script_location  //More error prone

5. Use lowercase letters in URIs

   When convenient, lowercase letters should be consistently preferred in URI paths.

   RFC 3986 defines URIs as case-sensitive except for the scheme and host components. e.g.

   http://api.example.org/my-folder/my-doc  //1
   HTTP://API.EXAMPLE.ORG/my-folder/my-doc  //2
   http://api.example.org/My-Folder/my-doc  //3

   In above examples, 1 and 2 are same but 3 is not as it uses My-Folder in capital letters.

6. Do not use file extentions

   File extensions look bad and do not add any advantage. Removing them decreases the length of URIs as well. No reason to keep them.

   Apart from above reason, if you want to highlight the media type of API using file extenstion then you should rely on the media type, as communicated through the Content-Type header, to determine how to process the body’s content.

   http://api.example.com/device-management/managed-devices.xml  /*Do not use it*/
   http://api.example.com/device-management/managed-devices   /*This is correct URI*/

Never use CRUD function names in URIs

URIs should not be used to indicate that a CRUD function is performed. URIs should be used to uniquely identify resources and not any action upon them. HTTP request methods should be used to indicate which CRUD function is performed.

HTTP GET http://api.example.com/device-management/managed-devices  //Get all devices
HTTP POST http://api.example.com/device-management/managed-devices  //Create new Device
HTTP GET http://api.example.com/device-management/managed-devices/{id}  //Get device for given Id
HTTP PUT http://api.example.com/device-management/managed-devices/{id}  //Update device for given Id
HTTP DELETE http://api.example.com/device-management/managed-devices/{id}  //Delete device for given Id

Use query component to filter URI collection

Many times, you will come across requirements where you will need a collection of resources sorted, filtered or limited based on some certain resource attribute. For this, do not create new APIs – rather enable sorting, filtering and pagination capabilities in resource collection API and pass the input parameters as query parameters. e.g.

http://api.example.com/device-management/managed-devices
http://api.example.com/device-management/managed-devices?region=USA
http://api.example.com/device-management/managed-devices?region=USA&brand=XYZ
http://api.example.com/device-management/managed-devices?region=USA&brand=XYZ&sort=installation-date