In the mid-1970s he authored the first Hungarian Prolog interpreter and led the development of the MProlog system, a pioneering Hungarian software product sold worldwide in the 1980s. His main fields of interest include declarative programming (logic programming, constraint programming, the Prolog language); semantic technologies (Semantic Web, semantic integration); exploiting parallelism and programming languages supporting parallelism; as well as implementation of programming languages. He is the author and co-author of about 90 peer-reviewed publications, including 14 books/book chapters and eight journal publications. In recognition of his pioneering work in the field, he was honoured by the Association of Logic Programming as one of the fifteen Founders of Logic Programming.