Time is an important entity in everyday life. Everyone of us has to check calendars, diaries, timetables etc. on a daily routine. Therefore it is not surprising that temporal information has also made its way into many information management systems. A recent reminder of this fact are the many discussions around the implication of what is called the ``date crisis'', the ``year-2000-bug'' or the ``millenium timebomb'', as in [Glass, 1997], [Clark, 1997], [Uhlig, 1997] and many more.
In this chapter, we focus on time data stored in databases. It is intended to serve as a general introduction to the research area of temporal databases. Furthermore, it will introduce some basic concepts that are used throughout the remainder of this thesis.