Relational database system for a social network via which a number of users can share data with each other, wherein the data are stored in data blocks in tables having a plurality of rows, the data assigned to a user are stored as data blocks in the database system, the data blocks assigned to a user can be managed exclusively by the user, the sharing of data of the data blocks between users in the social network is defined by predetermined data chains, wherein each data chain specifies data from the data associated with a user that the user shares and specifies the user with whom the data is shared, wherein each data chain thus also represents a connection between the users and the data chains are formed within the network, wherein each data chain is stored as a table in the relational database system and can be managed exclusively by the user to whom the data is assigned, wherein the sharing creates a new table with the data according to the data chain and wherein at least one data chain is assigned a program which executes predetermined functions on the basis of the data specified by the data chain, wherein one of the functions is a payment mechanism that implements a transaction in cryptocurrency between at least two users, wherein the data chain with the corresponding data blocks can be fixed such that it cannot be modified by any user, wherein the database system in the social network confirms, through the fixed data chain with the corresponding fixed data blocks, an agreement made between the one user and the user with whom the data is shared, and wherein the fixed data chain with the corresponding fixed data blocks is secured on a blockchain that is independent of the database system. the data are stored in data blocks in tables having a plurality of rows, the data assigned to a user are stored as data blocks in the database system, the data blocks assigned to a user can be managed exclusively by the user, the sharing of data of the data blocks between users in the social network is defined by predetermined data chains, wherein each data chain specifies data from the data associated with a user that the user shares and specifies the user with whom the data is shared, wherein each data chain thus also represents a connection between the users and the data chains are formed within the network, wherein each data chain is stored as a table in the relational database system and can be managed exclusively by the user to whom the data is assigned, wherein the sharing creates a new table with the data according to the data chain and wherein at least one data chain is assigned a program which executes predetermined functions on the basis of the data specified by the data chain, wherein one of the functions is a payment mechanism that implements a transaction in cryptocurrency between at least two users, wherein the data chain with the corresponding data blocks can be fixed such that it cannot be modified by any user, wherein the database system in the social network confirms, through the fixed data chain with the corresponding fixed data blocks, an agreement made between the one user and the user with whom the data is shared, and wherein the fixed data chain with the corresponding fixed data blocks is secured on a blockchain that is independent of the database system.