This paper presents an ontology for systems engineering, by means of a set of information models based on a modelling methodology derived from and a simplification of the ISO 15926 part 2 data model. The methodology matches the way people think and communicate and is designed specifically to be useful for engineers. The information models are derived from ISO 15288 System Life Cycle Processes. Based on the information models and the set of relationships defined herein one can, in combination with a reference data library, build or configure an information system or data exchange mechanism in order to support Systems Engineering processes or set up a specific product knowledge model. An implementation method based on RDF is given as example.