---
layout: default
navsection: api
navmenu: Concepts
title: Resources

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h1. Resources

This page describes the common attributes of Arvados resources.

The list of resource types is on the "front page of the API Reference":./.

h2. Object IDs

Object IDs are alphanumeric strings, unique across all installations (each installation has a unique prefix to prevent collisions).

h2. Attributes of resources

table(table table-bordered table-condensed).
|*Attribute*|*Type*|*Description*|*Example*|
|uuid|string|universally unique object identifier|@mk2qn-4zz18-w3anr2hk2wgfpuo@|
|href|string|a URL that can be used to address this resource||
|kind|string|@arvados#{resource_type}@|@arvados#collection@|
|etag|string|The ETag[1] of the resource|@1xlmizzjq7wro3dlb2dirf505@|
|self_link|string|||
|owner_uuid|string|UUID of owner (typically User or Project)|@mk2qn-tpzed-a4lcehql0dv2u25@|
|created_at|datetime|When resource was created|@2013-01-21T22:17:39Z@|
|modified_by_client_uuid|string|API client software which most recently modified the resource|@mk2qn-ozdt8-vq8l5qkzj7pr7h7@|
|modified_by_user_uuid|string|Authenticated user, on whose behalf the client was acting when modifying the resource|@mk2qn-tpzed-a4lcehql0dv2u25@|
|modified_at|datetime|When resource was last modified|@2013-01-25T22:29:32Z@|

h2. Attributes of resource lists

table(table table-bordered table-condensed).
|*Attribute*|*Type*|*Description*|*Example*|
|kind|string|@arvados#{resource_type}List@|@arvados#projectList@|
|etag|string|The ETag[1] of the resource list|@cd3o1wi9sf934saajykawrz2e@|
|self_link|string|||
|next_page_token|string|||
|next_link|string|||
|items[]|list|List of resources||


h2. ETags

fn1. Each response includes an ETag, a string which changes when the resource changes.  Clients can use this to check whether a resource has changed since they last retrieved it.  If a previous ETag is provided along with a request, and the resource has not changed since, the server may return a "not modified" response.