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Wikimedia Commons is a database of 56,102,378 media files. In order to make easier a selection process, these files are organized according various criteria (see Commons:Categories#Category structure).

This page explains the classification principles of a major part of this organization: the topics structure.


The basic element of this classification is the subject, an area of study which can be easily defined unambiguously.

The classification process consists in:

  • grouping media files by subject: allocate appropriate subjects to each media file
  • providing an easy access to these “subjects”, or groups of media files

Subjects will be choosed as much as possible amongst encyclopedic subjects which have an article in at least one Wikipedia. In any case, subjects must be useful to the classification process.

Relationships between subjectsEdit

The organization of Knowledge is an issue which concerns librarians for centuries, and they have used elaborate systems like the Dewey Decimal Classification or the Universal Decimal Classification.

These classification systems aim particularly to indicate relationships between subjects, because such relationships match the functionning of mind: a dog is much more related to a emu than to a crystal ball, and such assertion is generally regarded as true in most cultures.

In Commons Wikipedia, the set of subjects is organized according to relationships between subjects, a binary relation, or association of elements within the set of subjects with elements of the same set.