Abstract: An entity-relation database is disclosed to include a plurality of entity fields containing arrays of data elements, the data elements being related to each other in predefined sets, with each predefined set including data elements in at least two of the entity fields. At least one linked list defines the relationship between data elements between each of the predefined sets and provides a means for retrieving all of the elements of any selected predefined set from the two entity fields. The linked list consists of two distinct portions, namely, a head portion associated with each member of one entity field and a continuation portion associated with each member of another entity field, while each entry consists of a pair of addresses thereby forming a doubly linked list.

Abstract: Plural digital signals are converted to plural analog signals through a plurality of sample and hold circuits, there being one for each of the desired conversions, which sequentially sample a periodic signal on a repetitive basis in response to a sample control signal, and a plurality of digital counters, each being associated with a different one of the sample and hold circuits for receiving one of the digital signals and providing a digital count of clock pulses indicative thereof when enabled to provide the sample control signal upon the completion of its count, with each enabling period being initiated at the same cyclical point of the periodic signal and wherein the number of clock pulses generated in one cycle of the periodic signal is equal to the maximum count for the digital counters.