\chapter{Introduction}
\label{ch:introduction}

\section{Motivation}
\label{sec:motivation}

\section{Contribution}
\label{sec:contribution}
The goal of this work is to define the requirements for a hybrid solution and to prove its feasibility in the form of a prototype. Within the scope of the concept for a hybrid solution, the requirements for the \ac{OSN}, the app and the network for secure data exchange have to be defined, and potential problems and limitations have to be identified. Based on these requirements, the elaboration of solution strategies for the implementation is possible. 

For the prototype, an Android application that exchanges private data with other users via a \ac{P2P} network is created.  The previously defined requirements should be fulfilled in the best possible way. Both the selection of the \ac{OSN} and the technologies used need to be carefully evaluated.

With the Hybrid \ac{OSN} app for Twitter, we present a solution that allows private data to be shared securely with other users of the same app without complicated configuration. Thus, everyone can protect their privacy and still use the usual features of the \ac{OSN}.

\section{Outline}
\label{sec:outline}
The remainder of this thesis is structured as follows. In Chapter \ref{ch:background}, a comprehensive overview of different network and system architectures is given for a better understanding of this work. In particular, the basics of software system architectures and their characteristics are described, as well as \ac{P2P} networks and \acp{dApp}.  Chapter \ref{ch:related-work} is about relevant work and projects in the context of this thesis. In Chapter \ref{ch:concept}, the general concept of a hybrid OSN is discussed, and requirements to the solution are defined. Furthermore, several solution strategies are carried out. Chapter \ref{ch:proof-of-concept} describes our implementation of the concept in the form of an Android app for the hybrid use of Twitter. The design decisions and architecture are considered as well.  Chapter \ref{ch:evaluation} evaluates the Hybrid \ac{OSN} prototype with the previously defined requirements. Besides, the limitations and threats are discussed. Finally, Chapter \ref{ch:conclusions} summarizes this work and gives an outlook for future work.