Abstract: An aggregation operation is performed on a subset of facts sampled from a full structured collection of facts, to determine an aggregation result. Based on the determined aggregation result and on an indication of characteristics of the sampled subset of facts relative to the full structured collection of facts, an indication of a difference is determined, between what would be the result of the aggregation-type operation on the full structured collection of facts and the actual result of the aggregation-type operation on the sampled subset of facts. The full structured collection of facts may be comprised of a plurality of component structured collections of facts, where the sampled subset of facts includes facts that are sampled from the plurality of component structured collections of facts, in a manner that is deterministic across the component structured collections of facts, and then joined to constitute the sampled subset of facts.

Abstract: An aggregation operation is performed on a subset of facts sampled from a full structured collection of facts, to determine an aggregation result. Based on the determined aggregation result and on an indication of characteristics of the sampled subset of facts relative to the full structured collection of facts, an indication of a difference is determined, between what would be the result of the aggregation-type operation on the full structured collection of facts and the actual result of the aggregation-type operation on the sampled subset of facts. The full structured collection of facts may be comprised of a plurality of component structured collections of facts, where the sampled subset of facts includes facts that are sampled from the plurality of component structured collections of facts, in a manner that is deterministic across the component structured collections of facts, and then joined to constitute the sampled subset of facts.

Abstract: A seismic prospecting roll along switch incorporating electronically controlled switches in an improved switch arrangement requiring far fewer switches than previous systems. In a simple form, one switch is provided for each geophone input with one contact of each switch connected to one of the inputs and the other contact of each switch connected in pairs, appropriately selected, to the inputs of amplifier and filter channels. A controller is provided for electronically closing the appropriate switches for each roll along position. In most roll along positions geophone inputs are connected out of order to the signal processing channels and the sequence is corrected by a modified multiplexer which connects the processing channels to a system analog to digital converter.

Abstract: Apparatus and method for detecting errors in addressing as well as transfer and storage of data. Both odd and even parity are alternately assigned to data words as a function of the memory address where a particular data word is stored. A parity error on reading occurs when either an error has occurred in the data word itself or when the memory has been incorrectly addressed.