OAI / Open Archives Initiative -- A particular initiative to make information about electronic resources widely available, using the OAI protocol (see Open Archive and OAI protocol for Metadata Harvesting). The Initiative website is at http://www.openarchives.org/
OAI Protocol for Metadata Harvesting -- The protocol defines a mechanism for harvesting records containing metadata from repositories. The link between this metadata and the related content is not defined by the OAI protocol.
OAI and the OAIS differentiated -- The OAIS stands for the 'Open Archival Information System'. This is a reference model and conceptual framework for an archival system dedicated to preserving and maintaining access to digital information over the long term. Brian Lavoie of OCLC defines its purpose as: "to increase awareness and understanding of concepts relevant for archiving digital objects, especially among nonarchival institutions; elucidate terminology and concepts for describing and comparing data models and archival architectures; expand consensus on the elements and processes endemic to digital information preservation and access; and create a framework to guide the identification and development of standards." [Meeting the challenges of digital preservation: the OAIS reference model, originally published in the OCLC Newsletter, No. 243: 26-30 (January/February 2000)].
Thus the aim of the OAIS is quite different from that of the Open Archives Initiative. The OAIS also uses the term "Archive" in a quite different sense, more in line with that used by the archiving profession, where it has connotations of long term preservation. See "Archive" in this glossary.
Open Archive -- an 'open archive' is one for which metadata is publicly available (i.e., 'exposed') to researchers via a service provider. The 'open' part of this technical term refers to the architectural aspect of the open archives idea - the definition and promotion of machine interfaces which facilitate the availability of content from a variety of providers. 'Open' does not mean 'free' or available for unlimited use. 'Archive' reflects the origins of the OAI - in the E-prints community the term 'archive generally means 'a repository of scholarly papers' - but the OAI uses the term in a broader sense as a repository for stored information.