The Semantic Web and ontologies are emerging technologies which enable advanced knowledge management and sharing. Their application to Astronomy can offer new ways of sharing information between astronomers, but also between machines or software components and allow inference engines to perform reasoning on an astronomical knowledge base. This document presents the current status of an ontology describing knowledge about astronomical object types, originally based on the standardization of object types used in the SIMBAD database. Specifically, this ontology of defined concepts is designed to enable advanced reasoning on astronomical object types. The possibilities offered by such a system are semi-automatic or fully-automatic applications such as checking the semantic consistency of databases entries, providing new means of building or refining queries and suggesting object types matching a description.