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Tag URI is a universal unique identifier protocol commonly used in various internet-related technologies and associated with data storage and transfer systems such as YAML.[1][2]

According to RFC 4151, a tag is a type of Uniform Resource Identifier (URI) designed to meet the following requirements:[3]

  1. Identifiers are likely to be unique across space and time, and come from a practically inexhaustible supply.
  2. Identifiers are relatively convenient for humans to mint (create), read, type, remember etc.
  3. No central registration is necessary, at least for holders of domain names or email addresses; and there is negligible cost to mint each new identifier.
  4. The identifiers are independent of any particular resolution scheme.


The following is an example tag that could be "minted" by a user to indicate authorship of a resource on the World Wide Web. The semantics of Tag URI do not require the user to currently have ownership of the Hostname upon which the tag is based, due to the date qualifier:


The following example is a similar tag minted to indicate the name of the pet gerbil of the same user. Note that the semantics of Tag URI do not require the tagged entity to be accessible electronically:


This demonstrates that the Tag URI scheme can be used to tag any entity, object or concept.

See also[edit]


  1. ^ "Tag". Retrieved 2007-11-02. 
  2. ^ "YAML specification". Retrieved 2007-11-02. 
  3. ^ RFC 4151 - The 'tag' URI Scheme