Categorization
There are several proposals for how to do categorization in Wikipedia (and, by extension, for other MediaWiki sites).
By hand
"List of X" articles give hand-build categorization.
Automatically, "Category:" pseudo-namespace
Magnus Manske did an automated categorization tool using a "Category:" pseudo-namespace.
Categorization with field-value pairs
Would apply field-value pairs for categorization. See Categorization with field-value pairs.