---
layout: default
navsection: api
navmenu: Concepts
title: Common resource fields

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This page describes the common attributes of Arvados resources.

h2(#resource). Resource

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@|
|owner_uuid|string|UUID of owner (must be a User or Group)|@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. Object UUID

Each object is assigned a UUID.  This has the format @aaaaa-bbbbb-ccccccccccccccc@.
format.

# The first field ("aaaaa" in the example) is the site prefix.  This is unique to a specific Arvados installation.
# The second field ("bbbbb" in the example) is the object type.
# The third field ("ccccccccccccccc" in the example) uniquely identifies the object.

h2. Timestamps

All Arvados timestamps follow ISO 8601 datetime format with fractional seconds (microsecond precision).  All timestamps are UTC.  Example date format: @YYYY-mm-ddTHH:MM:SS.SSSSZ@

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.