Difference between revisions of "XMP"

XMP (Extensible Metadata Platform) facilitates embedding metadata in files using a subset of RDF. Most notably XMP supports embedding metadata in PDF and many image formats, though it is designed to support nearly any file type.

Creative Commons is recommending XMP as the preferred format for embedded metadata, given its support for numerous file formats and the balkanized state of embedded metadata standards. Others are coming to a similar conclusion; Microsoft has announced support for XMP in Vista applications and Jon Udell notes "There’s also good support in .NET Framework 3.0 for reading and writing XMP metadata." Note that even when embedded with XMP metadata, Creative Commons recommends a licensed document include a visible copyright notice; format-specific recommendations for visible notices are available.

The Creative Commons licensing process offers a XMP template which may be used to mark files within XMP-supporting Adobe applications (step-by-step how-to document).

Specifying License Information

XMP defines a rights management schema (see section 4.2.5). Creative Commons sets the following properties (example values):

• xapRights:Copyright — This work is licensed to the public under the Creative Commons Attribution-ShareAlike license http://creativecommons.org/licenses/by-sa/2.0/ verify at http://example.com/pdf-metadata.html (Replace URL following 'verify at' with URL containing metadata about the XMP-embedded file; this is typically the same URL specified by xapRights:WebStatement.)
• xapRights:Marked — False if Public Domain, True otherwise.
• xapRights:WebStatement — http://example.com/pdf-metadata.html (Replace with URL containing metadata about the XMP-embedded file; this is referred to as the Web Statement.)

We also define a Creative Commons schema http://creativecommons.org/ns# whose common prefix is cc. It currently has the following properties:

• license — The license URL; for example, http://creativecommons.org/licenses/by-sa/2.0/.
• morePermissions — A URL where additional permissions (commercial licensing, etc) are available.
• attributionURL — The URL to use when attributing this work.
• attributionName — The creator's preferred name to use when attributing this work.

Verification Links and XMP

A publisher can add boost confidence in embedded metadata by providing a verifying web statement. A verifying web statement is a URL which contains metadata with assertions matching those embedded in the file. The difference is that instead of making the assertions about a URL, the assertions are made in reference to the SHA-1 hash of the file.

For example, the example web statement http://example.com/pdf-metadata.html would include metadata encoded as RDFa.

  <p>The document example.pdf is licensed under a 
     <a about="urn:sha1:MSMBC5VEUDLTC26UT5W7GZBAKZHCY2MD" rel="license" 
        href="http://creativecommons.org/license/by/3.0/">
          Creative Commons Attribution 3.0</a> license.
     </a>
  </p>

When processing a file containing an embedded web statement, an application can retrieve the statement and parse it for additional metadata. If matching assertions are found which apply to the calculated SHA-1 hash of the file, the application can display an indicator noting increased confidence in the metadata. This approach has the added benefit of taking advantage of an existing mechanism (copyright take-down procedures) in order to break the confidence in the case of inappropriately licensed material.

Additional Information

• XMP Implementations
• All XMP-related articles

The XMP logo is either a registered trademark or trademark of the Adobe Systems Incorporated in the United States and/or other countries.