Horst received a Ph.D. in computer science from the Technische Universität of Berlin in 1985 where he has been a senior research scientist ever since.  His research interests are information retrieval systems, software engineering, software metrics and the measurement of the quality of software during the software life-cycle.

From 1987 to 1988 he was with IBM Thomas J. Watson Research in Yorktown Heights.  In 1991 he published the book Software Complexity, Measures and Methods (De Gruyter).  From 1989 until 1992 he was with the ESPRIT II Project 2384 METKIT (Metric-Educational-Toolkit) of the European Commission.  Then from August 1994 to December 1994 he was invited to be a researcher by the Gesellschaft für Mathematik und Datenverarbeitung (GMD) in St. Augustin, Germany.

In 1998 he published his second book A Framework for Software Measurement (DeGruyter).  From February 1998 to May 1998 he was a visiting professor at the University of Southwest Louisiana in Lafayette, Louisiana.  In December 1998 he received his habilitation (Privatdozent) in the area of Praktische Informatik (Practical Computer Science) from the department of computer science at the Technische Universität, Berlin.