Multimedia Database Systems as the tool to extract and generate additi
onal values from multimedia 'Contents' are discussed in this paper wit
h putting emphasis on the mediator functions between users and content
s. Firstly, we discuss about 'what to do' from the view point of four
promising contents sources: 'on the network,' 'in the digital broadcas
ting' 'in the library' and 'in the real world.' From this view point,
four types of multimedia database systems are defined. 'What to do' fo
r each database system is also discussed. Two concrete multimedia data
base systems with unique mediator functions, stream-type multimedia da
tabase platform GOLS and the intelligent access and authoring system u
sing multiple media synchronization are proposed with experimental eva
luation results and concrete multimedia database applications.