TIMECENTER Participants

Any software made available via TimeCenter is provided \as is " and without any express or implied warranties, including, without limitation, the implied warranty of merchantability and tness for a particular purpose. The TimeCenter icon on the cover combines two \arrows. " These \arrows " are letters in the so-called Rune alphabet used one millennium ago by theVikings, as well as by their precedessors and successors. The Rune alphabet (second phase) has 16 letters, all of which have angular shapes and lack horizontal lines because the primary storage medium was wood. Runes may also be found on jewelry, tools, and weapons and were perceived by manyashaving magic, hidden powers. The two Rune arrows in the icon denote \T " and\C, " respectively. Most real-world databases record time-varying information. In such databases, the notion of \the current time, " or NOW, occurs naturally and prominently. For example, when capturing the past states of a relation using begin and end time attributes, tuples that are part of the current state have some past time as their begin time and NOW as their end time. While the semantics of such variable databases has been described in detail and is well understood, th