This paper presents the theoretical and methodological considerations on the implementation of a controlled vocabulary for medieval administrative acts expressed in imperial diplomas. The controlled vocabulary constitutes an expansion of the ontological module for the bibliographic description of medieval charters related to Germanic emperors, OntoVE_WrittenRecords, described in De Bastiani (2023, 2025). It is being conceived in order to overcome the limitations of the so far implemented bibliographic module. In fact, the bibliographic module currently in use models the acts as events, but does not allow for finer grained inquiries on the data. While the controlled vocabulary is still under construction, this paper presents the theoretical and methodological underpinnings for its implementation, starting from the literature on ontologies and the semantic modelling of medieval charters.