Stop those Control Freaks
Suppose, you are in a meeting with other people. You need more information on the Hubble constant and ask the audience for details. Someone (maybe a friendly physics professor) comes to the white board and explains the theory.
Hmmh, how does that relate to software architecture? If you think about the situation, you'll recognize that the solution is based on a decentralized approach.
Normally, we are more used to centralization. Maybe, we are even addicted to all those centralized concepts. There is a central directory server, a central hub in the EAI solution, a central database, ... But as the example illustrates, sometimes decentralization is the better choice.
In the real life example we have used a P2P concept by leveraging broadband communication - ok, you just spoke very loud so that everyone paid attention to your question. Is this the only way to implement decentralization? No, there are several other alternatives.
For example, Swarm Intelligence: Suppose, I can't remember where I have parked my car. To increase search speed, all family members will visit different areas to locate the car. All searchers carry mobile phones to communicate with each other. After my wife found the car, she tells everyone where it is.
Another example could be Ad Hoc Networking: In the nearby forest, I find an interesting bird. I tell other people approaching my location about the bird who themselves tell other people who ... After a short period of time the scene is crowded with interested people.
Decentralized thinking means getting rid of central nodes or central controls. This might increase fault tolerance, but decrease efficiency. Often centralized concepts are mixed with decentralized ones. For example, there might be registries where all possible peers in a P2P network are known.
From an architecture viewpoint, several patterns support decentralization. For instance, the Lookup/Locator pattern, Blackboard architecture pattern, or the Leader/Followers pattern.
One of the qualities we can get from a decentralized system is emergence. The system as a whole reveals smart behavior that is more than just the combination of all nodes. Think of swarm intelligence like in an ant population.
From my viewpoint, decentralization is still neglected in software engineering, especially in software architecture. And as the examples shows, real life offers an abundance of decentralized concepts.