The Digital Discovery System (DDS) software is an XML repository search server that provides a search API built on top of Lucene. A DDS repository can be populated through a repository service API or by pointing it to XML files on disc. It is optimized to support the rapid construction of audience-specific portals and applications and can be flexibly configured to search over any XML structure. An instance of the DDS is hosted at nsdl.org to provide the Search API over library collections. The DDS software may also be downloaded for use locally.