Nevertheless spreadsheets were originally designed for computing purposes and for commercial applications, they are often used in industry to implement Information Systems, thanks to the functionalities offered by integrated scripting languages and ad-hoc frameworks (e.g., Visual Basic for Applications). This technological solution allows the adoption of Rapid Application Development processes for the quickly development of Spreadsheets-based Information Systems, but the resulting systems are quite difficult to be maintained and very difficult to be migrated to other architectures such as Database-oriented Informative Systems or Web applications. In this paper we present an approach for reverse engineering the data model from an Excel spreadsheet-based system in the context of a process of migration to a Web based application based on a MVC architecture. The proposed approach was successfully applied in a real context of a company operating in the automotive industry. The main contribution of this paper is represented by the Data Model Reverse Engineering activity that is the basis of the Migration process.