It is crucial for ontology engineers to compose these heterogeneous ontologies for effective and scalable interoperability among Web agents. In this paper, we propose a combination framework based on effective and scalable ontology interoperability for high-quality query answering. We also put forward a specifical process to substantiate our combination approach. The underlying theoretical and empirical analyses are exploited for ensuring effectiveness and correctness of the approach. Experimental results from our prototype system show that high-quality query results but sacrifice some of reasoning complexity.