Temporal database research has seen an explosive growth in the 1980s and 1990s; however, most of this research has failed to make its way to commercial database systems. In particular, there is not a well-accepted temporal query language that will allow such tasks as the extraction of temporal information from databases at different granularities or the extraction of time interval information from time instant data. These tasks are important on their own but also as a data preprocessing step, prior to data mining. Therefore, the temporal data owner is left on her own to devise a solution to extract this kind of information from a standard database system. Another recently emerging need is the extraction of temporally semantic information, that is, information within the context of a temporal ontology. In Section 1.2 of this chapter, we discuss the concept of a temporal database mediator, which is a computational layer placed between the user interface and the database for the discovery of temporal relations, temporal data conversion, and the discovery of semantic relationships.