"The discovery layer still uses the information and indexing in the integrated library system (ILS), but it also searches across proprietary databases and other electronic resources, all with the goal of revealing everything that a library owns or has licensed on a given topic be it a print monograph, an electronic journal article, streaming video, or a collection of archival documents"

The discovery layer can be looked on as the replacement for the OPAC.Some libraries maintain both a catalog interface OPAC and a discovery layer interface.