VirtualMedia: Making Multimedia Database Systems Fit for World-Wide Access

In the age of the world-wide web global media data—often called media assets—, stored in multimedia database management systems (MM-DBMS), will increasingly be made accessible to virtually everyone. Hence, lots of heterogeneous clients with different, not safely predictable capabilities of storing, processing, and presenting media data are willing to access these MM-DBMSs (which may be part of a digital library). In general, there exist two categories of client applications. The first only want to retrieve media objects for presentation or possibly printing. The second (additionally) create media objects or modify them through editing and/or composition. Assuming a sort of unbalance between these application types sounds reasonable: Usually there will be many applications of the presentation type and much less of the other type. Thus, one could be tempted to optimize the system(s) for presentation only. This would, however, most likely result in missing the much stronger quality and performance demands of media editing applications. Consequently, media servers being an (essential) part of multimedia database management systems should provide physical data independence. Today’s media servers—especially continuous media servers—, however, do not provide physical data independence at all. One—if not the main—reason for this is performance. Physical data independence without optimization undoubtedly costs a lot of performance. Therefore, this optimization problem (and solving it) is both initiator and quintessence of the VirtualMedia approach. Obviously, we are facing considerable problems on attempting to provide physical data independence with a media server (or MM-DBMS, respectively): Such systems tend to require frequent format conversions inevitably resulting in bad performance. They may inadvertently lose data due to irreversible updates. Moreover, hiding the internal data representation from the client also means that all the strongly necessary optimization is to be accomplished by the server, which is both more difficult and more promising than leaving optimization to the applications. The following section summarizes some recent approaches to solve (some of) these problems. Section 3 briefly introduces VirtualMedia, followed by concluding remarks.