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Last Updated: May 19, 2022

Objects are the basic unit for data storage in Object Storage Service (OSS). Objects are also known as files. OSS stores all elements as objects in buckets, and does not use a hierarchical structure to store objects.

Object types

Objects can be classified into the following three types based on how they are created:

  • Normal: Objects of this type are created by using simple upload.

  • Multipart: Objects of this type are created by using multipart upload.

  • Appendable: Objects of this type are created by using append upload. You can append content to objects only of the Appendable type.


An object cannot be converted to a different object type. For example, a normal object cannot be converted to a multipart object or an appendable object.

Object information

An object consists of the following information:

  • Key: the name of the object. You can use the object key to query the object.

  • Data: the content that is stored in the object. The content is a sequence of bytes.

  • Version ID: the ID of the object version. After you upload an object to a versioned bucket, OSS generates a version ID for the object.

  • Object metadata: the metadata of the object. Object metadata is a set of key-value pairs that define the attributes of the object, such as the time when the object is last modified and the object size. You can add custom information to object metadata.

Access control

OSS allows you to use the following access control methods to manage access to objects in buckets: bucket policies, access control lists (ACLs), Resource Access Management (RAM) policies, temporary access authorization based on Security Token Service (STS), and hotlink protection. Bucket policies and ACLs are implemented based on resources. RAM policies are implemented based on users. Hotlink protection is implemented by using whitelists. For more information about access control, see Overview.

Authorized access

By default, the ACLs of OSS resources such as buckets and objects are set to private. To allow unauthorized users to access these resources, you must grant permissions on these resources to the users. For example, if you store image and video resources of your websites in OSS buckets, you can use one of the following methods to authorize third-party users to access the resources: