A query processing system has a query processor and a data manager. The tongues, grooves, ridge and channel respectively are dimensioned so as to inter-engage when logs are placed one on top of another. During real time monitoring of various performance data, the system can also identify unsatisfactory performance conditions, i. The first operating unit operates whether a signal level of the input signal is sustained equal to or longer than a predetermined period based on the first and second signals, and outputs an output signal in synchronization with the clock signal when the signal level of the input signal is sustained equal to or longer than the predetermined period. In another embodiment, at least one of the elevator and the spider is remotely controllable. Embodiments of the present invention provide for the hierarchical set of slides to be navigated by a user via a keyboard, touchscreen, or other communication means.