Access to distributed and heterogeneous Internet resources is coming up as one of the major problem for future development of the next generation of Digital Libraries. Available data sources vary in terms of data representation and access interfaces, therefore a system for federating heterogeneous resources accessible via the Web is considered to be a crucial aspect in digital libraries research and development. Libraries as well as institutions and enterprises are struggling to find solutions that can offer the final user an easy and automatic way to rapidly find relevant needed resources among heterogeneous ones. Our project starts from the recent results of Dublin Core Metadata Initiative (DCMI) and in particular from the Dublin Core Recommendations (DCMIR). This paper reports our analysis of three different digital historical archives maintained by the European University Institute (EUI) in Florence and its mapping using a common Meta Resource Card based on Dublin Core Elements (DCMES). This situation requires careful consideration of interoperability issues related to uniform naming, metadata formats, document models and access protocols for the different data sources. We also present our Porta Europa Portal (PEP) federated architecture that will support an XML Dublin Core implementation and in our aim should be easily open to RDF future support. The PEP pilot project specialised portal should provide high quality information, selected according to the criteria of originality, accuracy, credibility together with the cultural and political pluralism derived from the EUI’s profile. The information in Porta Europa will be relevant, reliable, searchable and retrievable.