Provided by the University of Michigan Digital Library Production Service, OAIster is a union catalog of freely available digital resources and a search tool. It was originally funded by the Andrew Mellon Foundation and has been searchable since the summer of 2002 .
OAIster uses the Open Access Initiative Protocol for Metadata Harvesting (OAI-PMH) protocol to harvest metadata. The system harvests Dublin Core encoded metadata in XML format from OAI-enabled metadata repositories. XSLT is used to transform the DC metadata into DLXS Bibliographic Class encoded metadata. Metadata is indexed and made accessible through an interface using the XPAT search engine. It is an open source system including the framework, harvester tool, and transformation tool .
OAIster has harvested and indexed over 13 million records from over 900 contributors. These academically-oriented resources are from digital collections that are often hidden in the deep web and include:
- digitized books and articles
- born-digital texts
- audio files
- datasets 
Content is not limited by subject. It is also not limited to metadata. Instead, direct access to the online representation is provided.
 Search Tool
OAIster's search tool was designed to decipher the metadata tags used to label scholarly materials . It offers keyword and field based searching using Boolean operators. There are options to limit search by resource type: text, image, audio, video, and dataset. The results may be sorted by hit frequency, title, author/creator, and date.
1. Hagedorn, Kat. 2003. OAIster: A "no dead ends" OAI service provider. Library Hi-Tech 21(2): 170-181.
2. University of Michigan Digital Library Production Service. 2007. OAIster. http://www.oaister.org/.
3. Young, Jeffrey R. 2004. Libraries try to widen Google's eyes. Chronicle of Higher Education 50(37): A1-A32.