This paper shows how to combine ontological and model-based techniques in languages that facilitate collaborative design exploration. The proposed approach uses ontology to capture alternative designs and incremental refinements that meet requirements and earlier design commitments. Model-based techniques are applied to develop more powerful, engineering-friendly languages for using ontology. It uses ontology's open world semantics to support design collaboration with flexible and accurate design combination, refinement, and consistency checking. It also leads to more reliable interpretation of models across the product lifecycle due to more rigorous language semantics. An example language is described using these techniques.