Here we look at the concept of federation, from both social, political and a technical point of view.
# Political Federation
A federal state is a political entity characterized by a union of partially self-governing states or regions under a central (federal) government. Alternatively, federation is a form of government in which sovereign power is formally divided between a central authority and a number of constituent regions so that each region retains some degree of control over its internal affairs - wikipedia
With the United States Constitution having become effective on 4 March 1789, the United States is the oldest surviving federation. On the other end of the timeline is Nepal, which became the newest federation after its constitution went into effect on 20 September 2015.
# Social Federation A socially federated architecture is also known as community.
When Margret Thatcher famously said "There is no such thing as society" she was alluding to a philosophical tradition that was fighting against the ontological and political claims that there was this "thing" society which could act or be an object of legitimate scrutiny. There were just individual people, the invisible hand of the market, and networks of relations between people - a "living tapestry of men and women".
When we think of federation in a social (or deliberative) context, we picture a small group of people meeting, developing relationships and a common understanding. A dialogue or interaction between such groups, will have different properties to a dialogue between a network (or "rich tapestry") of individuals. These are all different network topologies, with consequentially different behaviours.
# Technical Federation
Some comments on federation in the technical sense over at psyc.eu
# Federated Wiki
The web is a federated document database. Pages from wildly different sites are shown in a single browser interface.
Federated Wiki goes a step further, federating the read/write web. Documents from many different servers are pulled together into your browser. Clicking into edit one from another server brings a copy of it to your server, while preserving pointers and history from the server it came from.
The same way the web browser introduced one interface that made the web seem like one gigantic site (even though it was multiple servers) federated wiki introduces an interface that makes the federation seem like one giant wiki site, even though it is on multiple servers.
Of course, federating the read/write web is a bit more radical, and more apt to give you one of those ice cream headaches when you think hard about it. But thinking about why the web browser approach was so powerful in 1989 may help you understand what Federated Wiki is attempting.