Grounding the development of mobile and ubiquitous services on actual needs and behaviors of users, rather than on designers' intuition, is a well-established tradition. However, gathering data about users in different contexts usually results in large amounts of data that have to be analyzed and translated into requirements. This crucial activity and its outcome are often shaped by the preconceptions of the developers or researchers. Despite this subjectivity, the translation process is seldom transparent. The aim of this paper, therefore, is to contribute to the field by presenting a process for translating user expressions into needs and later into requirements using Reiss' taxonomy of human needs. By adopting this process of translation, we were able to identify two hierarchical levels of needs: needs of a service and needs in a service. These two levels provide a transparent bridge between user expressions and system requirements.