Nielsen SoundScan is an information and sales tracking system created by Mike Fine and Mike Shalett. Soundscan is the official method of tracking sales of music and music video products throughout the United States and Canada. Data is collected weekly and made available every Wednesday to subscribers, which include executives from all facets of record companies, publishing firms, music retailers, independent promoters, film and TV, and artist management. SoundScan is the sales source for the Billboard music charts, making it the official source of sales records in the music industry.

Nielsen SoundScan began tracking sales data for Nielsen since March 1, 1991. The May 25 issue of Billboard published Billboard 200 and Country Album charts based on SoundScan "piece count data," and the first Hot 100 chart to debut with the system was released on November 30, 1991. Previously, Billboard tracked sales by calling stores across the U.S. and asking about sales - a method that was inherently error-prone and open to outright fraud.^{[citation needed]}

Keith L. Clark is a Professor of Computer Science at Imperial College London, England. He has lectured in both mathematics and computer science. Since 1979 he has had a tenured position in the Department of Computing, Imperial College London, where he has been Professor of Computational Logic since 1987. Between 1987 and 1995 he was also Visiting Professor at Uppsala University. He is currently a Visiting Professor at BTH (since 1997), and at the University of Queensland (since 1998). In 1980 he co-founded an Imperial College spin-off company, Logic Programming Associates, to develop and market Prolog systems for micro-computers (micro-Prolog) and to provide consultancy on expert systems and rule based applications.

His key contributions have been in the field of logic programming. His 1978 paper on negation as failure was arguably the first formalisation of a non-monotonic logic. His 1981 paper on a relational language for parallel programming introduced concurrent logic programming.

Recently he has been working on the April and Go! programming languages and their application to agent programming.