Driven by application requirements and using well-understood theoretical results, 
we describe a novel methodology and a tool for modular ontology design. 
We support the user in the safe use of imported symbols 
and in the economic import of the relevant part of the imported ontology. 
Both features are supported in a well-understood way: 
safety guarantees that the semantics of imported concepts is not changed, 
and economic import guarantees that no difference can be observed between 
importing the whole ontology or importing the relevant part.