This work develops a support system for robotic assembly program synthesis. The system is based on the conceptual graph theory. The proposed intelligent system for robotic assembly (ISRA) provides a means to automatically (guided by knowledge) convert a user's request, expressed in the natural language, to the appropriate conceptual model of thee requested task. This model incorporates the information required for understanding, planning, and sensory-guided controlling the required robotic task. Such a model has to be suitable (e.g., representable and executable) for an efficient computer processing. Hence, to complete justification of the proposed approach, problems of complexity of the ISRA algorithm, existence of the canonical solutions, crashing, finiteness, and correctness must be studied in this paper, we present a formal approach to evaluate the complexity of conceptual graph-based algorithms of IISRA type, and a case study that illustrates the approach.