Nowadays, learning and teaching outcomes are defined predominantly by target competencies. In order to assess learning outcomes, properly defined and empirically validated competency models are required. For object-oriented programming, such models have not been brought forward up to now. Aiming to develop a competency structure and level model for this field, we have examined the structural knowledge of programming novices to derive its potential dimensions. The results suggest 6 dimensions. Additionally, we propose difficulty levels for two of these dimensions based on the SOLO taxonomy. The empirical validation of these dimensions and their levels is subject to further investigations.