---
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.