After thinking some more about the merits of the augmenting the category system or creating a new system, I thought of the following: The Category tag can only ever represent an "is a" relationship. By adding the Category:Human tag to Liam Neeson, we are really trying to convey that Liam Neeson IS A human. The category system is perfect for defining this kind of information. However, the category system cannot be used to define any other kind of relationship. For example, in the Anne Frank article, it is not currently possible in wikipedia to have an "author of" relationship. It would therefore be a good idea to add an AuthorOf tag to wikipedia. There are many other relationships like this that could be defined. Each such relationship should have a well defined domain and co-domain (For those that are unfamiliar with these terms, I will explain them with an example). Consider the "Author of" relationship: (Lewis Carroll) AuthorOf (Alice's Adventures in Wonderland) AuthorOf is a relation, that maps a Person to a Book. We say that the domain of AuthorOf is People, and the co-domain of AuthorOf is Books. Each new relation defined in wikipedia would have to have a domain and a co-domain associated with it. For the sake of example, I will create the following syntax to define a new relationship: Relation: AuthorOf Domain: Person CoDomain: Book Because we have defined the domains of the AuthorOf relation, we can now do some very powerfull stuff with wikipedia: Imagine Dave is a user of wikipedia, who does not know about defining categories. He is doing some research on the web on his favourite author, Lewis Carroll, and notices that there is no page on wikipedia about him. He goes ahead and creates the page, and he also creates two pages for Lewis' most famour books: Alice's Adventures in Wonderland and Through the Looking Glass. Dave does not add his new pages to any category. At the same time Mike is looking at the recent changes, and sees the new editions on Lewis Caroll, and decides to have a look at the pages. He notices that Dave has not defined the AuthorOf relationship, so on the Lewis Caroll page Mike adds: [[AuthorOf:Alice's Adventures in Wonderland]] [[AuthorOf:Through the Looking Glass]] Remember that Wikipedia knows that the domain of the AuthorOf relation is Person, and that the co-domain is Book, so it can automatically add Category:Person to Lewis Caroll, and Category:Book to Alice's Adventures in Wonderland and Through the Looking Glass We can also define an inverse of AuthorOf: consider the revised syntax: Relation: AuthorOf Inverse: WrittenBy Domain: Person CoDomain: Book Now when someone defines that Lewis Carroll was the AuthorOf Through the Looking Glass, Wikipedia will automatically know that Through the Looking Glass was written by Lewis Carroll. Mikes adds the tag [[AuthorOf:Through the Looking Glass]] to Lewis Caroll, and Wikipedia will automatically add [[WrittenBy:Lewis Carrol]] to the Through the Looking Glass page. What does anyone else think? -- Marc O'Morain