1. An in-memory data warehouse system comprising: one or more processors; and a computer-readable medium coupled with the processor, the computer-readable medium comprising instructions stored thereon that are executable by the one or more processors to cause the in-memory data warehouse system to perform operations comprising: storing a plurality of virtual data model views as part of a virtual data model layer configured to enrich application data with time-dependent data having a validity period; wherein each virtual data model view of the plurality of virtual data model views comprises a keep history flag as a property of each data model view that is only set if time-dependent data is maintained for the application data associated with the virtual data model view; receiving an indication that the keep history flag has been activated in a first virtual data model view of the plurality of virtual data model views, wherein the first virtual data model view is based on one or more tables; based on determining that the keep history flag has been activated in the first virtual data model view, generating a shadow table with a same structure as the first virtual data model view; determining that updates were made to at least one table upon which the first virtual data model view is based; determining whether the updates made to the at least one table have an effect on the first virtual data model view; and updating the shadow table, based on determining that updates made to the at least one table have an effect on the first virtual data model view.