Semantic trajectory data can be exploited in the decision-making process in various application domains such as traffic management, healthcare, urban planning, banking, bird migration, natural disaster and so on. To take advantages of efficient inference from semantic trajectory data in the decision-making process, a higher level of abstraction when modelling this sort of data is an emerging need. An important issue of trajectory data modelling is the heterogeneity of the large number of information generated by the moving object. Ontologies permit overpowering heterogeneity of data as well as provide semantics to the design. This fact leads us to propose in this paper a new ontology-based approach to model and to query a semantic trajectory data warehouse. We validate our bid by a case study dealing with the trajectory of the Tunisian Kuwaiti Bank (BTK) mobile publicity car for children education saving plan.