If I want my OAI repository to serve a metadata format other than oai_dc, what do I need to do?
OAI-PMH requires schemas for all metadata served, so you must indicate an XML schema for the metadata format, and each of your metadata records must validate to its indicated schema. This means the xsi:schemaLocation attribute must be provided for served metadata. OAI-PMH requires that this attribute be present on the “metadata” elements. We reiterate: your metadata must validate to an XML schema to adhere to OAI-PMH.