We present a proposal for selecting ERP products from a formal description of their relevant characteristics. The work is based on a previous and successful collaboration with a midsize company in the field of software package selection. An ERP was selected following a systematic methodology called SHERPA. In this past experience, SHERPA relied on natural language descriptions of the application domain, user needs and candidate ERP solutions. Now, we show that a formal language may be used for modeling this application domain, translating user needs into requirements over the ERP products, and for reflecting how concrete ERP products adjust to them. Having selection criteria used during ERP acquisition formally modeled, as well as user needs and ERP product descriptions, we expect to obtain more reliable and understandable results in this process.