This document presents FOWLA (Federated Architecture for OWL Ontologies), an approach for ontology federation that addresses semantic heterogeneity. FOWLA defines autonomous ontologies that are aligned through rules, allowing inference across ontologies. Queries can be expressed using terms from any aligned ontology. Rule selection reduces query execution time compared to using all alignment rules. The approach was demonstrated by aligning ifcOWL and COBieOWL ontologies for building information modeling. FOWLA enables deducing new knowledge, flexible query composition, and reduced query response times.