We present a generic portal system architecture suitable for geoscientific data portals. The portals harvest data providers with Open Archives Initiative (OAI) protocols using XML based metadata formats like DIF or ISO-19139 format. Current implementations of OAI only support Dublin Core metadata. The new Java based portal software will support any XML format and makes them searchable through Apache Lucene without any other database software. The open architecture makes it possible to define searchable fields in several data formats by XPath allowing full text queries on all types of fields including numerical ranges. The metadata of all providers are stored in separate indices which makes it possible to combine them in several different portals. The web service interface allows to support custom front-ends for users and additional visualization in maps. The software will be made freely available through the Open-Source concept. A use case describes how the generic software is used in the Collaborative Climate Community Data and Processing Grid (C3-Grid).