Fig. 4

Schema graph \(\mathbf {RG_2}\) transformation. The transformation of the schema graph \(\mathbf {RG_2}\) is depicted in two steps. The left panel displays the merge of hubs and directly connected sinks into new entity nodes (blue) in \(\mathbf {RG_2}\) 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., OrderPatient.PK and \(OrderPatient.order\_date\) became the edge labeled HasOrder with attribute \(order\_date\)) as shown in the right panel (step 7)