Domain ontology building is one of the most critical activities required in Semantic Web applications. The task must be performed by domain experts, who do not (generally) have the background of a knowledge engineer. To ease this task, Ontology Management Systems (such as Kaon, Protégé, OntoEdit, Athos) are developing user friendly interfaces. However the problem is mainly of a cognitive nature. Difficulties comes from the fact that the existing ontology languages: (i) are hard to be used by unskilled people, (ii) have very basic constructs (e.g., class, property), (iii) are not domain specific, i.e., they are conceived for very diverse contexts (e.g., from medical sector to high energy physics). OPAL (Object, Process, Actor modelling Language) aims at supporting business experts who need to build an ontology by providing a limited number of high level conceptual templates.