astronomy

Ole-Johan Dahl

Ole-Johan Dahl is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Ole-Johan Dahl rather than just read about it. In short: 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.

Key takeaways

Ole-Johan Dahl belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Ole-Johan Dahl to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Ole-Johan Dahl from memory before moving on to harder problems.

Reference excerpt

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. In 2001, Dahl and Nygaard won the ACM Turing Award.

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. 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. 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 languages, which began as an extended variant and superset of ALGOL 60. Dahl and Nygaard were the first to develop the concepts of class, subclass (allowing implicit information hiding), 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. 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) and was named Commander of the Royal Norwegian Order of St. Olav in 2000. The Association Internationale pour les Technologies Objets named the Dahl-Nygaard Prize after Dahl.

Early papers Dahl, O.-J (1957). Multiple index countings on the Ferranti Mercury computer. Oslo: Norwegian Defence Research Establishment. Dahl, O.-J.; Garwick, Jan V. (1958). Programmer's handbook for the Ferranti Mercury Computer, Frederic at the Norwegian Defense Research Establishment – 2nd ed., Kjeller. Norwegian Defence Research Establishment. Automatisk kodning: et prosjekt ved Forsvarets forskningsinstitutt. Bell, Vic; Dahl, Ole-Johan (1963). Simscript implementation (Report). Oslo: Norwegian Computing Center. Dahl, Ole-Johan; Nygaard, Kristen (1965). Basic concepts of Simula: an ALGOL based simulation language. Oslo: Norwegian Computing Center. Simula: a language for programming and description of discrete event systems: introduction and user's manual. Oslo: Norwegian Computing Center. 1965. Dahl, Ole-Johan (1966). Discrete event simulation languages: lectures delivered at the NATO summer school, Villard-de-Lans, September 1966. Oslo: Norwegian Computing Center. Dahl, Ole-Johan; Nygaard, Kristen (1966). Simula: an ALGOL based simulation language. Oslo: Norwegian Computing Center. Dahl, Ole-Johan; Nygaard, Kristen (1966). "Simula: an ALGOL-based simulation language". Communications of the ACM. 9 (9). New York: Association for Computing Machinery: 671–678. doi:10.1145/365813.365819. S2CID 11032334. Dahl, Ole-Johan; Nygaard, Kristen (May 1967). "Class and subclass declarations". Written at Oslo. In Buxton, J. N. (ed.). I: Simulation programming languages: Proceedings of the IFIP working conference on simulation programming languages. Amsterdam: North-Holland (published 1968). Organized by IFIP Technical Committee 2, programming languages; O.-J. Dahl, conference chairman. Dahl, Ole-Johan (1968). Genuys, F. (ed.). Discrete event simulation languages. London: Academic Press (Programming languages: NATO Advanced Study Institute. Dahl, Ole-Johan; Myhrhaug, Bjørn; Nygaard, Kristen (1968). Simula 67: Common Base Language. Oslo: Norwegian Computing Center (Publication S; Revised 1970, Publication 22.

See also List of pioneers in computer science

References

Sources From Object-Orientation to Formal Methods: Essays in Memory of Ole-Johan Dahl, Olaf Owe, Stein Krogdahl and Tom Lyche (eds.), 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 Homepage – comprehensive amount of info, pictures, and biblio

Worked examples

Example 1 — a first encounter with Ole-Johan Dahl

Start with the simplest possible case. Write down what Ole-Johan Dahl claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Ole-Johan Dahl before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Ole-Johan Dahl ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Ole-Johan Dahl

In research: Ole-Johan Dahl appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Ole-Johan Dahl in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Ole-Johan Dahl is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1931 births, 2002 deaths, Academic staff of the University of Oslo, so understanding it makes those chapters shorter.
In everyday life: Look for Ole-Johan Dahl outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Ole-Johan Dahl in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Ole-Johan Dahl means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Ole-Johan Dahl out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Ole-Johan Dahl in simple terms?

Why does Ole-Johan Dahl matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Ole-Johan Dahl?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Ole-Johan Dahl.