Professional operators who deal with the cultural goods of Italy constantly face the problem of retrieving the needed information from heterogeneous sources. Such information has also to be combined and elaborated; this operation is made difficult by the heterogeneity of the data models and vocabularies employed at the different information sources.

This paper illustrates the architecture of a web-based system that provides users with a unified view of the metadata describing the information available from the various sources. In this way the user can navigate through and choose among homogeneous virtual descriptions that finally bring him/her to the sought real data.

The peculiarities of the illustrated system are: it is built exclusively employing open source software, it allows the data sources to maintain their "independence", i.e., they remain the unique managers of their own data, it supports different virtual communities of users, each with its own vocabulary and ontology.