Abstract <p>The subject domain, which can contain from one to several dozen or even hundreds (for large-scale systems) of subject lists, is a mandatory, core component of the vast majority of existing databases, around which all other components of the latter are built. The multilevel representation of objects in such databases is a standard practice aimed to simultaneously reflect both the numerous classifications that accompany subject lists and the key, basic relationship of materialization, which connects prototypes, models of subjects, and their instances. In spite of the existence of many methods for configuring subject schemes, the question of the invariance of such constructions is still relevant. In this paper, we show that the relationship of materialization is not the only constant in subject schemes. Multilevel models must include several standard relationships, such as relationships of variability and personification, which, together with the relationship of materialization, form an invariant framework of the subject scheme.</p>