A type of collection that describes, and points to features of another collection.REFERENCE. Research Data Alliance http://smw-rda.esc.rzg.mpg.de/index.php/Main_Page ; Rajasekar, R., M. Wan, R. Moore, W. Schroeder, S.-Y. Chen, L. Gilbert, C.-Y. Hou, C. Lee, R. Marciano, P. Tooby, A. de Torcy, B. Zhu, “iRODS Primer: Integrated Rule-Oriented Data System”, Morgan & Claypool, 2010.