Dahl was born in Mandal, Norway. He was the son of Finn Dahl and Ingrid Othilie Kathinka Pedersen. When he was seven, his family moved to Drammen. When he was thirteen, the whole family fled to Sweden during the Occupation of Norway by Nazi Germany. After the end of the war, Dahl studied numerical mathematics at the University of Oslo. Dahl became a full professor at the University of Oslo in 1968 and was a gifted teacher as well as researcher. Here he worked on Hierarchical Program Structures, probably his most influential publication, which appeared co-authored with C.A.R. Hoare in the influential book Structured Programming of 1972 by Dahl, Edsger Dijkstra and Hoare, perhaps the best-known academic book concerning software in the 1970s. As his career progressed, Dahl became increasingly interested in the use of formal methods, to rigorously reason about object-orientation for example. His expertise ranged from the practical application of ideas to their formal mathematical underpinning to ensure the validity of the approach. Dahl is widely accepted as Norway's foremost computer scientist. With Kristen Nygaard, he produced the initial ideas for object-oriented programming in the 1960s at the Norwegian Computing Center as part of the Simula I and Simula 67simulationprogramming languages. Dahl and Nygaard were the first to develop the concepts of class, subclass, inheritance, dynamic object creation, etc., all important aspects of the OO paradigm. An object is a self-contained component in a software system. These are combined to form a complete system. The object-oriented approach is now pervasive in modern software development, including widely used imperative programming languages such as Java and C++. He received the Turing Award for his work in 2001. He received the 2002 IEEE John von Neumann Medal and was named Commander of the Royal Norwegian Order of St. Olav in 2000.
SIMULA: an ALGOL based simulation language / by Ole-Johan Dahl and Kristen Nygaard. Oslo: Norsk Regnesentral, 1966.
Simula: an ALGOL-based simulation language / Ole-Johan Dahl and Kristen Nygaard. New York: Association for Computing Machinery, 1966. I: Communications of the ACM; 9.
Class and subclass declarations / Ole-Johan Dahl and Kristen Nygaard. Amsterdam: North-Holland, c1968. I: Simulation programming languages: proceedings of the IFIP working conference on simulation programming languages, Oslo, May 1967 / O.-J. Dahl, conference chairman; organized by IFIP Technical Committee 2, programming languages; edited by J.N. Buxton.
SIMULA 67: common base language / by Ole-Johan Dahl, Bjørn Myhrhaug and Kristen Nygaard. Oslo: Norsk Regnesentral, 1968. Rev. 1970: Common base language.
