A diagram of hyperlinks would show it's complexity.
>>> issubclass(wiki, database)
True
>>>
"""Ward Cunningham, the developer of the first wiki software, WikiWikiWeb, originally described it as "the simplest online database that could possibly work"."""
The SQL is just the datastore. The wiki is the real database. Now to show that the wiki is a complex database, you would show a diagram of all the hyperlinks between pages... and the many other ways the data is linked (categories, tags etc)
Personally, what I find surprising about this whole thing is that people are so amazed at the simplicity of the schema. A wiki is a fairly simple application. Think about it. If you were going to build one it's not much more than a basic CRUD application. You really only have articles (with versioning), user accounts, images/media and whatever other oddball features you want to have like statistics and IP restrictions. Hell, I remember seeing some beginning Ruby on Rails book that used a wiki as the tutorial application. This is pretty basic stuff.
The relations(links) are like the relations in an SQL database. The relations in the wikitext are like database relations.
Much of the logic is built into the document attributes(wikitext), coded in the php layer. Mediawiki is a very big, and complex database. 1.5 million LOC. Which is fairly small compared to other databases.
Anyway... I guess my point is that mediawiki is a database, and that it's relations are not in the SQL - but in the wikitext.
see you!