Organizing objects using prefixes - Amazon Simple Storage Service

Organizing objects using prefixes

You can use prefixes to organize the data that you store in Amazon S3 buckets. A prefix value is similar to a directory name that enables you to group similar objects together in a bucket. When you programmatically upload objects, you can use prefixes to organize your data.

The prefix limits the results to only those keys that begin with the specified prefix. The delimiter causes a list operation to roll up all the keys that share a common prefix into a single summary list result.

The purpose of the prefix and delimiter parameters is to help you organize and then browse your keys hierarchically. To do this, first pick a delimiter for your bucket, such as slash (/), that doesn't occur in any of your anticipated key names. Next, construct your key names by concatenating all containing levels of the hierarchy, separating each level with the delimiter.

For example, if you were storing information about cities, you might naturally organize them by continent, then by country, then by province or state. Because these names don't usually contain punctuation, you might use slash (/) as the delimiter. The following examples use a slash (/) delimiter.

  • Europe/France/Nouvelle-Aquitaine/Bordeaux

  • North America/Canada/Quebec/Montreal

  • North America/USA/Washington/Bellevue

  • North America/USA/Washington/Seattle

If you stored data for every city in the world in this manner, it would become awkward to manage a flat key namespace. By using Prefix and Delimiter with the list operation, you can use the hierarchy you've created to list your data. For example, to list all the states in USA, set Delimiter='/' and Prefix='North America/USA/'. To list all the provinces in Canada for which you have data, set Delimiter='/' and Prefix='North America/Canada/'.

Listing objects using prefixes and delimiters

A list request with a delimiter lets you browse your hierarchy at just one level, skipping over and summarizing the (possibly millions of) keys nested at deeper levels. For example, assume that you have a bucket (ExampleBucket) with the following keys.

sample.jpg

photos/2006/January/sample.jpg

photos/2006/February/sample2.jpg

photos/2006/February/sample3.jpg

photos/2006/February/sample4.jpg

The sample bucket has only the sample.jpg object at the root level. To list only the root level objects in the bucket, you send a GET request on the bucket with "/" delimiter character. In response, Amazon S3 returns the sample.jpg object key because it does not contain the "/" delimiter character. All other keys contain the delimiter character. Amazon S3 groups these keys and returns a single CommonPrefixes element with prefix value photos/ that is a substring from the beginning of these keys to the first occurrence of the specified delimiter.

<ListBucketResult xmlns="http://s3.amazonaws.com/doc/2006-03-01/"> <Name>ExampleBucket</Name> <Prefix></Prefix> <Marker></Marker> <MaxKeys>1000</MaxKeys> <Delimiter>/</Delimiter> <IsTruncated>false</IsTruncated> <Contents> <Key>sample.jpg</Key> <LastModified>2011-07-24T19:39:30.000Z</LastModified> <ETag>&quot;d1a7fb5eab1c16cb4f7cf341cf188c3d&quot;</ETag> <Size>6</Size> <Owner> <ID>75cc57f09aa0c8caeab4f8c24e99d10f8e7faeebf76c078efc7c6caea54ba06a</ID> <DisplayName>displayname</DisplayName> </Owner> <StorageClass>STANDARD</StorageClass> </Contents> <CommonPrefixes> <Prefix>photos/</Prefix> </CommonPrefixes> </ListBucketResult>

For more information about listing object keys programmatically, see Listing object keys programmatically.