1. A computer-implemented method of mapping data within a data source to a target data model comprising: determining an identifier for each data object of the data source based on the data within that data object, wherein the identifier indicates a corresponding entity within a source ontology of a data model of the data source to which that data object belongs, wherein the source ontology includes a plurality of entities and relations between those entities, and wherein the determining the identifier includes: identifying for each data object a partition of one or more entities in the source ontology including a greatest amount of data from that data object; and determining the identifier for each data object based on the identified partition associated with that data object; comparing the determined identifiers for the data objects of the data source to a target ontology of the target data model to determine mappings between the data objects of the data source and the target data model; and extracting data objects from the data source for the target data model in accordance with the mappings.