1. A relational graph database system that manages a database containing graph data including node data connected through links to at least a first terminal device and a second terminal device, the relational graph database system comprising: a first processing unit comprising: at least one processor; a memory to store instructions to execute on the at least one processor, a node generation unit that generates node data corresponding to a prescribed operation of a node generation object in the first terminal device connected to a computer network; a partial graph generation unit that generates partial graph data including a plurality of node data having a prescribed relationship connected through links, wherein the plurality of node data corresponds to the prescribed operations conducted in the first terminal during a time interval; and a graph generation unit that synthesizes a plurality of partial graph data to generate graph data and stores the generated graph data that represents the plurality of node data and the links in the database, wherein the node generation unit generates a plurality of types of node data corresponding to a plurality of types of operations conducted in the second terminal device, when a plurality of operations conducted in the second terminal device has a prescribed relationship, the partial graph generation unit connects a plurality of node data corresponding to the plurality of operations conducted in the second terminal device through links to generate partial graph data, and the graph generation unit detects a common node in the plurality of partial graph data, and conducts graph synthesis of the plurality of partial graph data from the first terminal device and the second terminal device containing common node data of a common node in the plurality of partial graph data to generate graph data, and a second processing unit comprising: a reference node selection unit that selects a plurality of reference nodes from node data contained in the generated graph data based on input from the first terminal device, and an extraction unit that extracts a plurality of nodes having node data from the graph data based on centricity as determined from the plurality of reference nodes, wherein the extracted node data include strengths of relationships between the plurality of reference nodes and the extracted plurality of nodes.