Fig. 3

Schema graph \(\mathbf {RG_1}\) transformation. The transformation of the schema graph \(\mathbf {RG_1}\) is depicted in two steps. The left panel shows how hubs and directly connected sinks were merged into new entity nodes (blue) in \(\mathbf {RG_1}\) according to transformation step 6 (e.g., nodes Patient.id and Patient.attributes were merged into node Patient). Sources were transformed into edges connecting the previously created nodes directly (e.g., ProjectPatient.PK became the edge labeled InProject) as shown in the right panel (step 7)