Centralized VS decentralized VS distributed

I think bottom picture summarizes the concept very well.
We all know centralized systems so I will try to focus on Decentralized VERSUS Distributed systems.

“Decentralized” still includes the string “CENTRAL”.
It is something like “Semi-central” and “semi-distributed”.
In fact there are again “central authorities” (“semi-central”) but there is not just one single authority, there are many authorities and because of having many different independent authorities it is some kind distributed (“semi-distributed”)

“Distributed” systems have no authority, so keyword does not include string “CENTRAL”
Any combination of peer-to-peer(P2P) communication can occur but everyone has the data and processes the data separately and independently.
Everyone having data and processing separately means system is really and totally distributed.
Decisions after processing all distributed results may be centralized or decentralized but it does harm distributed processing systems.
Also decisions always require authorities. ( objects taking decisions are authorities.) Decision phase is different, processing phase is different.

Let’s look at blockchain example.
At blockchain, we heard terms like “DLT” and “DApps”. What is that “D” refer to? Is it same everywhere , if not why?
Every “D” does not mean same. It is sometimes “Decentralized” or sometimes “Distributed”

DLT=Distributed Ledger Technology
Every peer has ledger data and every peer process ledger separately and independently, so it is exactly distributed system.
DApps= Decentralized Applications
Companies making business together in blockchain write their own separate Smart Contract Applications.
Each company has separate business logic and separate decisions.
There may be many different co-operating companies ( = authorities ) writing their own Smart Contract ( = application )
So, application is absolutely decentralized.

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