The solution should meet specific functional and non-functional requirements so that users are willing to use another client.

\textbf{Functional requirements}:
\begin{itemize}
	\item \textbf{Standard functionality}: With the hybrid solution, all standard functionalities of the \ac{OSN} should be unrestrictedly usable. Otherwise, the user would be forced to continue using the original client. The parallel use of two clients for the same \ac{OSN} is not user-friendly and would be an argument against the use of the restricted hybrid client.
	\item \textbf{Client-side solution}: Since there is no control over the \ac{OSN}'s servers and software, changes can only be implemented on the client side. The alternative Facebook client app \enquote{Friendly for Facebook} for example changes the design on the client side and removes advertisements.
	\item \textbf{Data sovereignty}: The user can actively decide whether his data are stored on the \ac{OSN}'s servers or exchanged with other users via a private, secure channel. This implies that any functionality and the associated data exchange can also be carried out in a private, secure way. The user thus gains sovereignty over his data and can decide for himself whether to entrust it to the \ac{OSN}.
	\item \textbf{Authorized data access}: Especially the service provider of the \ac{OSN} should not have access to the private data of a user and should under no circumstances be able to relate them to him. As in the \ac{OSN}, the author himself should be able to determine with which users he shares his private data and grants them access.
	\item \textbf{Encryption}: Private data are a sensitive commodity and should, therefore, be protected in the best possible way. In particular, encrypted transmission and encrypted data storage are necessary to protect it from unauthorized access by third parties. It should be ensured that the encryption guarantees sufficient protection and is difficult for attackers to crack.
	\item \textbf{Flexible data format}: The future development of the \ac{OSN} is not foreseeable, and it is not able to take an influence on it. The data format for information exchange in the private network must therefore be able to react flexibly to possible changes. If, for example, dislikes can be assigned in addition to likes in the future or a new post type for videos is added, it should be possible to implement this quickly in the data structure of the hybrid solution.
	\item \textbf{Platform independence}: The hybrid solution should be platform-independent. Most \acp{OSN} have clients and web front ends to be accessed on all platforms. For a hybrid solution to be accepted and become a permanent alternative, it must work on the same platforms. Otherwise the user has to use the official clients again. A solution working on the computer at home that is not working on the smartphone restricts the user and avoids the adoption of the hybrid solution.
	\item \textbf{Anonymized data for the service provider}: A particular requirement is the provision of anonymized data from the private network for the service provider. In order to guarantee the operation of the platform, service providers must earn money. The hybrid solution should accept this circumstance and support it by the provision of anonymized data since data usually plays a central role in the business model. The service provider should be able to retrieve the anonymized data via a defined interface.
\end{itemize}

\textbf{Non-functional requirements}:
\begin{itemize}
	\item \textbf{Minimal additional effort}: Installation, configuration, and operation should be as simple as possible. Increased complexity is an additional barrier to the acceptance of the solution. All users of the \ac{OSN}, especially technically inexperienced users, should be able to use the hybrid solution. For the success of the hybrid solution, wide distribution is essential, so no user groups should be excluded.
	\item \textbf{Minimal side effects}: There should be no limitations for regular users who do not use the hybrid solution. Cryptic messages, disturbing content and other disturbing elements should be avoided. Annoying messages could lead to the user being blocked by other users or cutting off contact with them.
	\item \textbf{Free service}: Since the use of all significant \acp{OSN} is free of charge the user also expects the free use of a hybrid solution. Costs would have a deterrent effect in this use case and prevent the user from accepting the solution.
	\item \textbf{Compliance with policies}: By registering, the user agrees to the terms of service/use. It is important not to violate these conditions; otherwise, the user would have to bear the consequences. The severity of the consequences depends on the respective terms of use and the type of violation. For the hybrid solution, it is therefore essential to adhere to the \ac{OSN} terms of use as well. Otherwise, legal use is not possible.\\
	The Twitter Terms and Conditions allow the crawling of content within the rules set in the robots.txt file \cite{twitterXXXXtos}. Facebook completely prohibits the use of automated methods, thus excluding the possibility of crawling \cite{facebookXXXXtos}. Compliance with the guidelines therefore also directly restricts the possibilities of technical implementation. 
	\item \textbf{Good user experience}: The user should be offered the best possible user experience to increase the acceptance for the solution. A bad user experience causes frustration and will in the long run not lead to success of the hybrid solution. Good user experience includes:
	\begin{itemize}
		\item Short loading times, so waiting times are kept to a minimum. Hence, finding and loading data hast to be quickly.
		\item The user interface of the hybrid solution should be simple and understandable and have a modern and appealing design.
		\item When integrating into the \ac{OSN} user interface, the existing layout should not be broken, and additional control elements should be inserted in the same design.
		\item Privacy should be protected by design. The opposite is known as dark design pattern \enquote{Privacy Zuckering} (named after Facebook CEO Mark Zuckerberg), when controlling the privacy is purposely made difficult \cite{facebookXXXXzuckering}.
	\end{itemize}
\end{itemize}