Maintaining enterprise information systems over their life cycle requires proper modelling of the software components of these systems. Moreover, it requires proper modelling of the structure and functioning of the (extended) enterprise in which these systems are embedded. In this paper, the role of enterprise models in relation to enterprise information systems is compared with the role of product models in relation to physical products. Upgrading of physical products such as buildings requires modelling of these buildings in their physical environment. Upgrading of enterprise software requires a model of the software components in a run-time environment, which describes the extended enterprise.