Vietnamese Purple Star Astrology (VPSA) has long been revered as a potent tool for understanding destiny and unlocking the mysteries of individual lives. There have been some studies on astrology expert systems, but they are mainly based on classification algorithms and none for VPSA yet. This article is the first to propose a personalized expert system that utilizes ontology technology for VPSA. The system provides more profound and semantic insights by constructing a structured knowledge representation in an ontology that encapsulates the palaces and stars with their complex relationships. The expert system acts as an astrologer who can give predictions on various life aspects based on a specific VPSA chart. In this paper, we propose an architecture for a personalized VPSA expert system with knowledge representation, information extraction, and a reasoning machine. Our simulation example proves the benefits of an ontology-based approach, including the ability to systematically represent and reasoning capability.