Editing Ole-Johan Dahl

{{Short description|Norwegian computer scientist}}
{{Use dmy dates|date=April 2018}}
{{Infobox scientist
| name = Ole-Johan Dahl
| image = Ole-Johan Dahl.jpg
| birth_date = {{birth date |1931|10|12 |df=y}}
| birth_place = [[Mandal, Norway]]
| death_date = {{death date and age |2002|06|29 |1931|10|12 |df=y}}
| death_place = [[Asker]], Norway
| field = [[Computer science]]
| workplaces = [[Norwegian Computing Center]]<br/>University of Oslo
| education = [[University of Oslo]] ([[Bachelor of Science|BS]], [[Master of Science|MS]])
| known_for = [[Simula]]<br/>[[Object-oriented programming]]
| awards = [[Turing Award]] (2001)<br/>[[IEEE John von Neumann Medal]] (2002)
}}
'''Ole-Johan Dahl''' (12 October 1931 – 29 June 2002) was a Norwegian [[computer scientist]]. Dahl was a professor of computer science at the [[University of Oslo]] and is considered to be one of the fathers of [[Simula]] and [[object-oriented programming]] along with [[Kristen Nygaard]].<ref name="BioLexicon">
{{cite web |url=https://snl.no/Ole-Johan_Dahl |title=Ole-Johan Dahl |last=Nygaard |first=Kristen |website=Large Norwegian Encyclopedia |access-date=14 November 2020}}</ref><ref>
{{cite web |url=https://nbl.snl.no/Kristen_Nygaard |title=Kristen Nygaard |last=Rossen |first=Eirik |website=Norwegian Biographical Lexicon |publisher=Large Norwegian encyclopedia |access-date=1 May 2017}}</ref>

== Career ==
Dahl was born in [[Mandal, Norway]]. He was the son of Finn Dahl (1898–1962) and Ingrid Othilie Kathinka Pedersen (1905–80). When he was seven, his family moved to [[Drammen]]. When he was thirteen, the whole family fled to Sweden during the [[German occupation of Norway]] in [[World War II]]. After the war's end, Dahl studied numerical [[mathematics]] at the University of Oslo.<ref name="BioLexicon"/>

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 advanced, Dahl grew 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.<ref>{{cite web |url=https://www.mn.uio.no/ifi/english/about/ole-johan-dahl/ |title=Tribute to Ole-Johan Dahl |author=<!-- Unstated --> |date=2002 |publisher=University of Oslo |access-date=14 November 2020}}</ref>

Dahl is widely accepted as Norway's foremost computer scientist. With Kristen Nygaard, he produced the initial ideas for object-oriented (OO) programming in the 1960s at the [[Norwegian Computing Center]] (Norsk Regnesentral (NR)) as part of the [[Simula]] I (1961–1965) and Simula 67 (1965–1968) [[simulation]] [[programming language]]s, which began as an extended variant and [[Subset|superset]] of [[ALGOL 60]].<ref name="CommonBase">{{cite report |last1=Dahl |first1=Ole-Johan |author-link=Ole-Johan Dahl |last2=Myhrhaug |first2=Bjørn |last3=Nygaard |first3=Kristen |author3-link=Kristen Nygaard |date=1970 |url=http://www.edelweb.fr/Simula/#7 |title=Common Base Language |publisher=Norwegian Computing Center |page=1.3.1 |access-date=14 November 2020 |url-status=usurped |archive-url=https://web.archive.org/web/20131225084408/http://www.edelweb.fr/Simula/scb-1.pdf |archive-date=2013-12-25}}</ref> Dahl and Nygaard were the first to develop the concepts of [[Class (computer science)|class]], [[Subclass (computer science)|subclass]] (allowing implicit [[information hiding]]), [[Inheritance (object-oriented programming)|inheritance]], [[dynamic object creation]], etc., all important aspects of the OO paradigm. An ''object'' is a self-contained component (with a data structure and associated procedures or ''methods'') 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 [[C++]] and [[Java (programming language)|Java]].

He received the [[Turing Award]] for his work in 2001 (with [[Kristen Nygaard]]). He received the 2002 [[Institute of Electrical and Electronics Engineers]] (IEEE) [[John von Neumann Medal]] (with Kristen Nygaard)<ref>{{cite web |url=http://www.ieee.org/portal/pages/about/awards/pr/vonneupr.html |archive-url=https://web.archive.org/web/20060720182319/http://www.ieee.org/portal/pages/about/awards/pr/vonneupr.html |url-status=dead |archive-date=20 July 2006 |title=Recipients IEEE John von Neumann Medal|website=[[Institute of Electrical and Electronics Engineers]] (IEEE) }}</ref> and was named Commander of the [[Royal Norwegian Order of St. Olav]] in 2000.<ref>
{{cite web |url=https://amturing.acm.org/award_winners/dahl_6917600.cfm |title=Ole-Johan Dahl |last=Black |first=Andrew P. |date=2001 |website=ACM Awards |publisher=Association for Computing Machinery |access-date=14 November 2020}}</ref>

The [[Association Internationale pour les Technologies Objets]] named the [[Dahl-Nygaard Prize]] after Dahl.<ref>{{cite web |title=Dahl-Nygaard Prize |url=https://sites.google.com/aito.org/home/aito-dahl-nygaard?pli=1&authuser=1#h.mghfbijfburs |access-date=7 December 2022}}</ref>

==Early papers==
*{{cite book |last=Dahl |first=O.-J |date=1957 |title=Multiple index countings on the Ferranti Mercury computer |location=Oslo |publisher=[[Norwegian Defence Research Establishment]]}}
*{{cite book |last1=Dahl |first1=O.-J. |last2=Garwick |first2=Jan V. |date=1958 |title=Programmer's handbook for the Ferranti Mercury Computer, Frederic at the Norwegian Defense Research Establishment – 2nd ed., Kjeller |publisher=[[Norwegian Defence Research Establishment]]}}
*{{cite book |title=Automatisk kodning: et prosjekt ved Forsvarets forskningsinstitutt}}
*{{cite report |last1=Bell |first1=Vic |last2=Dahl |first2=Ole-Johan |date=1963 |title=Simscript implementation |location=Oslo |publisher=[[Norwegian Computing Center]]}}
*{{cite book |last1=Dahl |first1=Ole-Johan |last2=Nygaard |first2=Kristen |author2-link=Kristen Nygaard |date=1965<!--?--> |title=Basic concepts of Simula: an ALGOL based simulation language |location=Oslo |publisher=[[Norwegian Computing Center]]}}
*{{cite book |date=1965 |title=[[Simula]]: a language for programming and description of discrete event systems: introduction and user's manual |location=Oslo |publisher=[[Norwegian Computing Center]]}}
*{{cite book |last=Dahl |first=Ole-Johan |date=1966 |title=Discrete event simulation languages: lectures delivered at the NATO summer school, Villard-de-Lans, September 1966 |location=Oslo |publisher=[[Norwegian Computing Center]]}}
*{{cite book |last1=Dahl |first1=Ole-Johan |last2=Nygaard |first2=Kristen |author2-link=Kristen Nygaard |date=1966 |title=Simula: an ALGOL based simulation language |location=Oslo |publisher=[[Norwegian Computing Center]]}}
*{{cite journal |last1=Dahl |first1=Ole-Johan |last2=Nygaard |first2=Kristen |author2-link=Kristen Nygaard |date=1966 |title=Simula: an ALGOL-based simulation language |location=[[New York City|New York]] |publisher=[[Association for Computing Machinery]] |journal=Communications of the ACM |volume=9|issue=9 |pages=671–678 |doi=10.1145/365813.365819 |s2cid=11032334 |doi-access=free }}
*{{cite book |last1=Dahl |first1=Ole-Johan |last2=Nygaard |first2=Kristen |author2-link=Kristen Nygaard |editor-last=Buxton |editor-first=J. N. |chapter=Class and subclass declarations |publication-place=[[Amsterdam]], [[North Holland]] |publication-date=1968<!--?--> |title=I: Simulation programming languages: Proceedings of the IFIP working conference on simulation programming languages |place=Oslo |date=May 1967}} Organized by IFIP Technical Committee 2, programming languages; O.-J. Dahl, conference chairman.
*{{cite book |last=Dahl |first=Ole-Johan |editor-last=Genuys |editor-first=F. |date=1968 |title=Discrete event simulation languages |location=London |publisher=[[Academic Press]] (Programming languages: NATO Advanced Study Institute}}
*{{cite book |last1=Dahl |first1=Ole-Johan |last2=Myhrhaug |first2=Bjørn |last3=Nygaard |first3=Kristen |author3-link=Kristen Nygaard |date=1968 |title=[[Simula]] 67: Common Base Language |location=Oslo |publisher=[[Norwegian Computing Center]] (Publication S; Revised 1970, Publication 22}}

==See also==
* [[List of pioneers in computer science]]

==References==
{{Reflist}}

==Sources==
* ''From Object-Orientation to Formal Methods: Essays in Memory of Ole-Johan Dahl'', Olaf Owe, Stein Krogdahl and Tom Lyche (eds.), [[Springer Science+Business Media|Springer]], [[Lecture Notes in Computer Science]], Volume 2635, 2004. {{ISBN|3-540-21366-X}}. {{doi|10.1007/b96089}}.
* Pioneer who Prepared the Ground for Road to Java, [[Jonathan Bowen]]. ''[[The Times Higher Education Supplement]]'', 1677:34, 4 February 2005.

==External links==
* [https://web.archive.org/web/20181023114653/http://www.olejohandahl.info/ Homepage – comprehensive amount of info, pictures, and biblio]

{{ALGOL programming}}
{{University of Oslo}}
{{Software engineering}}
{{Turing Award laureates}}
{{Authority control}}

{{DEFAULTSORT:Dahl, Ole-Johan}}
[[Category:1931 births]]
[[Category:2002 deaths]]
[[Category:People from Mandal, Norway]]
[[Category:University of Oslo alumni]]
[[Category:Academic staff of the University of Oslo]]
[[Category:Norwegian computer scientists]]
[[Category:Programming language designers]]
[[Category:Turing Award laureates]]
[[Category:Formal methods people]]
[[Category:Dahl–Nygaard Prize]]