Configuring the set names and specs is done in the proai.properties file of the Fedora OAI provider plug-in. The following properties control how sets are defined.
The above properties are set to a Dublin Core or RELS-EXT field that define what setSpecs and setNames are available. For example, setting driver.fedora.setSpec = dc:type will expose all values of dc:type as setSpecs.
Another important property is driver.fedora.itemSetSpecPath which defines how items are related to sets. Following the example from above, setting driver.fedora.itemSetSpecPath = $item <dc:type> $setSpec means the $item’s dc:type has to match the given $setSpec to be considered part of that set.
The OAI provider documentation at http://www.fedora.info/download/2.2/services/oaiprovider/doc/index.html has more detail.