Ontologies reflect our view of what exists, and developing ontologies for a given domain requires a common context. This context can be characterized explicitly by means of an upper ontology. Upper ontologies define top-level concepts such as physical objects, activities, mereological and topological relations from which more specific classes and relations can be defined. As an effort to support the development of domain ontologies, we are developing an OWL ontology based on the ISO 15926 standard. This paper introduces the key aspects of the ontology, describes some of its main classes and properties and discusses its benefits and applications in the process engineering domain. (c) 2006 Elsevier Ltd. All rights reserved.