  The increasing amount of Linked Data and its inherent distributed nature have
attracted significant attention throughout the research community and amongst
practitioners to search data, in the past years. Inspired by research results
from traditional distributed databases, different approaches for managing
federation over SPARQL Endpoints have been introduced. SPARQL is the
standardised query language for RDF, the default data model used in Linked Data
deployments and SPARQL Endpoints are a popular access mechanism provided by
many Linked Open Data (LOD) repositories. In this paper, we initially give an
overview of the federation framework infrastructure and then proceed with a
comparison of existing SPARQL federation frameworks. Finally, we highlight
shortcomings in existing frameworks, which we hope helps spawning new research
directions.
