Storing metadata in files

Creative Commons

The non-profit Creative Commons organization distributes a variety of easily applicable free licenses for digital works [17] that artists and authors worldwide use to protect their copyrights. Creative Commons recommends XMP as a metadata format. At the same time, the organization posts guidelines on how artists can best utilize the information of the license they use [18] and embed this in their published files. This creates a win-win situation: The license strengthens the position of the author, and the users establish the license conditions in an uncomplicated and reliable way from the objects themselves.

Creative Commons has defined the XML namespace http://creativecommons.org/ns# for XMP, as well as for other purposes; this includes the following four elements cc:license, cc:morePermissions, cc:attributionURL, and cc:attributionName. The XMP Toolkit makes this namespace available under the consts.XMP_NS_CC key. Furthermore, the organization recommends the use of the two elements xmpRights:Marked and xmpRights:UsageTerms from the XMP rights management schema (Table 1).

A copy of the license notice should also (according to their advice) end up in dc:rights. Listing 3 shows a Python script that writes the metadata recommended by Creative Commons into a JPG file (not yet containing an XMP packet) with XMP Toolkit for the Attribution-ShareAlike 4.0 license. The result of these efforts is presented in Listing 4.

Listing 3

Generating Creative Commons-Compliant Metadata

 

Listing 4

Created XMP Package

 

The xmpRights:WebStatement text element transports a callable URL, by which details regarding the authorship and conditions of use of a file can be verified. The Creative Commons creators suggest installing a reference under the address given here that also contains the hash value of the published file [19]. In this case, it can be manually or automatically compared to raise the alarm in case of forgeries.

Conclusion

XMP involves a sophisticated and professional metadata system that compiles schemas for different objects and applications. The comprehensive set of descriptive components can even be expanded with elements not provided by the specification.

XMP supports a wide range of file formats in which to embed metadata packets; it is only on exceptional occasions that no solution exists. Nothing else is comparable, especially when it comes to PDF documents, although this is not surprising considering the standard's author (Adobe).

End users can request XMP metadata with ease from the command line, and programmers can develop special XMP applications with a range of C/C++ libraries. Python bindings are available for the existing XMP and Exif libraries, which can also handle XMP.

Exiftool (in the libimage-exiftool-perl Debian package or perl-image-exiftool package for openSUSE and others) and the command-line tool from the Exiv2 library (in the Debian exiv2 package) are also useful for editing XMP data at the command line.

The Author

Daniel Stender http://www.danielstender.com has been keeping busy e-documenting since finishing a humanities degree. He is a Debian developer and, among other things, the maintainer of the Python XMP Toolkit.

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