1. A computer implemented relation information constructing method for constructing, by computer processing, relation information between a plurality of data elements structured in a directed acyclic graph (DAG) in a first domain and a plurality of data elements structured in a DAG in a second domain on the basis of a preassigned relation between data elements, the method comprising: importing, using a processing device, data from the DAG of the first domain and data from the DAG of the second domain in order to generate a relation graph; in response to assignment of a relation between a node v a of the DAG of the first domain and a node v b of the DAG of the second domain, generating a join node between the node v a and the node v b in the relation graph, the join node being a node linking a node positioned upstream of the node v a in the DAG to a node positioned upstream of the node v b in the DAG; and as long as there is a pair of node v a of the DAG of the first domain and node v b of the DAG of the second domain that do not have a join node, generating a join node v between v a and v b in the relation graph, and generating an edge (v a , v) and an edge (v b , v) in the relation graph.