The classification of medieval inscriptions in digital epigraphic systems requires the alignment of local scholarly traditions with international standards. This issue becomes particularly acute when terminology is transferred between different classificatory frameworks. The aim of this article was to clarify the relationship between the terms “prayer” and “invocation” in the classification of graffiti from St. Sophia of Kyiv. The study was based on a comparative analysis of Korniyenko’s printed corpus and the digital portal “Inscriptions of St. Sophia”, which enabled the identification of differences in classification principles and the reconstruction of their conceptual foundations. It has been established that the terms “prayer” and “invocation” are not synonymous and reflect different classificatory logics. It has been shown that “prayer” is defined by a communicative criterion – the act of addressing God – and encompasses requests, confession, curses, and questions. In contrast, “invocation” is defined by a formal criterion – the presence of an address formula at the beginning of the text – and represents a subset of only one communicative type. The case of graffiti No. 5459 (“Lord, I am drunk”) has been analysed: in Korniyenko’s corpus, it is classified as a confessional inscription, whereas in the digital portal, it is categorised as an invocation. It has been demonstrated that both classifications are internally consistent but respond to different analytical questions, indicating that the discrepancy is epistemological rather than terminological. It has been substantiated that within Simple Knowledge Organisation System vocabularies, these concepts cannot be linked as skos:exactMatch or skos:closeMatch, but require a skos:relatedMatch relation with explicitly documented asymmetry. The practical significance of the results lies in their application to the development of controlled vocabularies and ontologies for digital epigraphy, particularly for aligning culturally grounded classification systems with international standards
epigraphy; epistemological bases for classification; digital epigraphy; controlled vocabulary; simple knowledge organisation system