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@@ -15,9 +15,11 @@ In a centralized application, the software essentially runs on a central node wi
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Typically, web applications are designed as centralized applications. The clients are usually (mobile) apps or browsers that act as the interface to the user. Examples are social networks such as Facebook and Twitter.
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-The advantages of a centralized architecture include that new clients can easily join the system simply by connecting to the server. Also, the maintenance of the software is easy to perform, since only the server node needs to be updated. These structures are also advantageous for the speed and the associated user experience since servers are generally reachable via fast connections, have sufficient resources and do not need to use complicated routes across several nodes. Due to the special role of the server, the authentication of a client in the system is easy to perform. Only the server has to check whether the client solely performs the actions to which it is authorized and can intervene if necessary. If a client is offline, this has no negative impact on the architecture because the software essentially runs on the server, clients only need to have low resources.
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+The advantages of a centralized architecture include that new clients can easily join the system simply by connecting to the server. Also, the maintenance of the software is easy to perform, since only the server node needs to be updated. These structures are also advantageous for the speed and the associated user experience since servers are generally reachable via fast connections, have sufficient resources and do not need to use complicated routes across several nodes. Due to the special role of the server, the authentication of a client in the system is easy to perform. Only the server has to check whether the client solely performs the actions to which it is authorized and can intervene if necessary. If a client is offline, this has no negative impact on the architecture because the software essentially runs on the server. Clients only need to have low resources.
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-The biggest disadvantage with this architecture is that failure or the blockade of the server leads to a collapses of the entire system. So, the server is the single point of failure of the whole system. Due to the design, the server has all the data. This makes him not only a popular target for hackers but also brings the clients into total dependency on the server. Having access to all the data can be used to provide an improved user experience by adapting the software to the user's needs. But it can also be used for targeted advertising or sensible data can even get sold to third parties. Furthermore, the server decides which data to send to the client, which brings with it the danger of censorship. As the number of clients increases, the server must scale to have sufficient resources.
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+The biggest disadvantage with this architecture is that failure or the blockade of the server leads to a collapses of the entire system. So, the server is the single point of failure of the whole system. Due to the design, the server has all the data. This makes him not only a popular target for hackers but also brings the clients into total dependency on the server.
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+With regard to web platforms like Facebook, having access to all the data can be used to provide an improved user experience by adapting the software to the user's needs. But it can also be used for targeted advertising or sensible data can even get sold to third parties. Furthermore, the server decides which data to send to the client, which brings with it the danger of censorship. As the number of clients increases, the server must scale to have sufficient resources.
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\subsection{Decentralized Applications}
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\label{sec:decentralized-applications}
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@@ -25,13 +27,13 @@ What are the advantages and disadvantages of centralized applications, is mostly
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Another advantage is that each server only handles the number of users covered by its resources. New servers contribute additional resources to the overall system. Distributed applications cannot be disabled easily because a new server can be started at any time that does not fall under a lock. Because the data are not centrally available, they cannot be processed, so that user data are better protected. Also, there is no longer a prominent attack target. So, hacking a single server loses lucrativeness.
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-The drawbacks include the difficulty of finding data because they are spread across multiple servers. Search functionalities are thus difficult to implement. If a server is taken offline, the data are no longer available, even if the system itself remains functional. Since there is no longer a central point that is managed by an operator, rolling out updates is difficult. This raises the challenge that server nodes of different versions of the same application can still work together.
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+The drawbacks include the difficulty of finding data because they are spread across multiple servers. Search functionalities are thus difficult to implement. If a server is taken offline, the data are no longer available, even if the system itself remains functional. To tackle this issue, data needs to be replicated. Since there is no longer a central point that is managed by an operator, rolling out updates is difficult. This raises the challenge that server nodes of different versions of the same application can still work together.
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-Examples of decentralized applications are the social networks diaspora* and Mastodon. In these networks, each user can operate a server on his own. Unlike Facebook, the decision on the existence of the service is therefore not in the control of the operator, but the user. Bitcoin is also a decentralized application architecture. In doing so, transactions are carried out in a decentralized database (blockchain).
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+Examples of decentralized applications are the social networks diaspora* and Mastodon. In these networks, each user can operate a server on his own. Unlike Facebook, the decision on the existence of the service is therefore not in the control of the operator, but the user.
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\subsection{Distributed Applications}
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\label{sec:distributed-applications}
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-A feature of distributed applications is the distributed computation across all nodes. At the same time, a single task is executed in parallel on several nodes of a system, and the entire system delivers the result in total.
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+A feature of distributed applications is the computation across all nodes. At the same time, a single task is executed in parallel on several nodes of a system, and the entire system delivers the result in total. The boundaries between decentralized and distributed networks are becoming blurred. A decentralized network consisting only of servers corresponds quasi to a distributed network.
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In distributed applications, there is no hierarchy with servers or clients. Each node is equal to the other nodes with everyone performing the same tasks. For this reason, a node in this architecture is called a peer. The structure is then referred to as \ac{P2P}. With such structures, there are no scaling problems, since each node contributes the required resources itself. Thus, the resources of the entire system grow with each new node added.
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