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Paper presented on the "I Krajowa Konferencja Naukowa Technologie Przetwarzania Danych, Poznań, 26-28.09.2005".
Virtual Schemas are part of the visual information retrieval system called Mavigator. The system is dedicated to naive users (computer non-professionals) and allows them to retrieve information from any data source, in particular, from object-oriented and XML-oriented databases. A significant problem related to all browsing tools is a way of presenting database schema graph. In many cases, there is a need to customize data-base schema, in particular, changing some names, adding new associations or removing some classes. Virtual Schemas allow creating a virtual customized version of existing database schema and navigate within the database according to this schema. Schema customization options include creating virtual association and virtual attributes, hiding/showing particular classes and renaming some schema items.