Method for integrating heterogeneous data sources (DS1...DSn) of automation technology into an automation system, the heterogeneous data sources (DS1...DSn) each comprising source data (SD1...SDn) of different data models, said source data (SD1...SDn) of the heterogeneous data sources (DS1...DSn) to be integrated being transformed by means of an integration middleware into a common data model, wherein the data sources (DS1...DSn) available in the automation system are identified by means of a discovery function implemented in the integration middleware and their source data (SD1...SDn) are loaded; the source data (DS1...DSn) of the data sources (SD1...SDn) whose data model is unknown is transformed by means of an ontology engine or by an ontology service into the common data model, with syntactic and semantic rules in the form of data mapping regulations being provided by the ontology engine or by the ontology service, by which rules the source data (SD1...SDn) is transformed into target data (TD1...TDn) of the common data model that corresponds syntactically and semantically to the common data model; a digital representative (DSDR1...DSDRn) in the form of an instance (DI, SI, VDI, SDI, ISCI) is generated with the common data model for each detected data source (DS1...DSn) by means of an instance manager implemented in the integration middleware and saved in a data abstraction layer; the target data (TD1...TDn) of each data source (DS1...DSn) is saved in the data abstraction layer in the respective digital representative (DSDR1...DSDRn); and the target data (TD1...TDn) is provided for at least one client tool (CT1...CTk) via an interface (CTI1...CTIk) which is designed to access the digital representative (DSDR1...DSDRn) of the target data (TD1...TDn) in accordance with the common data model. wherein the data sources (DS1...DSn) available in the automation system are identified by means of a discovery function implemented in the integration middleware and their source data (SD1...SDn) are loaded; the source data (DS1...DSn) of the data sources (SD1...SDn) whose data model is unknown is transformed by means of an ontology engine or by an ontology service into the common data model, with syntactic and semantic rules in the form of data mapping regulations being provided by the ontology engine or by the ontology service, by which rules the source data (SD1...SDn) is transformed into target data (TD1...TDn) of the common data model that corresponds syntactically and semantically to the common data model; a digital representative (DSDR1...DSDRn) in the form of an instance (DI, SI, VDI, SDI, ISCI) is generated with the common data model for each detected data source (DS1...DSn) by means of an instance manager implemented in the integration middleware and saved in a data abstraction layer; the target data (TD1...TDn) of each data source (DS1...DSn) is saved in the data abstraction layer in the respective digital representative (DSDR1...DSDRn); and the target data (TD1...TDn) is provided for at least one client tool (CT1...CTk) via an interface (CTI1...CTIk) which is designed to access the digital representative (DSDR1...DSDRn) of the target data (TD1...TDn) in accordance with the common data model.