Linked Data Fragments (LDFs) refer to Web interfaces that allow for accessing\nand querying Knowledge Graphs on the Web. These interfaces, such as SPARQL\nendpoints or Triple Pattern Fragment servers, differ in the SPARQL expressions\nthey can evaluate and the metadata they provide. Client-side query processing\napproaches have been proposed and are tailored to evaluate queries over\nindividual interfaces. Moreover, federated query processing has focused on\nfederations with a single type of LDF interface, typically SPARQL endpoints. In\nthis work, we address the challenges of SPARQL query processing over\nfederations with heterogeneous LDF interfaces. To this end, we formalize the\nconcept of federations of Linked Data Fragment and propose a framework for\nfederated querying over heterogeneous federations with different LDF\ninterfaces. The framework comprises query decomposition, query planning, and\nphysical operators adapted to the particularities of different LDF interfaces.\nFurther, we propose an approach for each component of our framework and\nevaluate them in an experimental study on the well-known FedBench benchmark.\nThe results show a substantial improvement in performance achieved by devising\nthese interface-aware approaches exploiting the capabilities of heterogeneous\ninterfaces in federations.\n