<P> Alan Kay, </P> <P> Another early MIT example was Sketchpad created by Ivan Sutherland in 1960--61; in the glossary of the 1963 technical report based on his dissertation about Sketchpad, Sutherland defined notions of "object" and "instance" (with the class concept covered by "master" or "definition"), albeit specialized to graphical interaction . Also, an MIT ALGOL version, AED - 0, established a direct link between data structures ("plexes", in that dialect) and procedures, prefiguring what were later termed "messages", "methods", and "member functions". </P> <P> In the 1960s object - orientated programming was put into practice with the Simula language, which introduced important concepts that are today an essential part of object - orientated programming, such as class and object, inheritance, and dynamic binding . Simula was also designed to take account of programming and data security . For programming security purposes a detection process was implemented so that through reference counts a last resort garbage collector deleted unused objects in the random - access memory (RAM). But although the idea of data objects had already been established by 1965, date encapsulation through levels of scope for variables, such as private (-) and public (+), were not implemented in Simula because it would have required the accessing procedures to be also hidden . </P> <P> In 1962 Kristen Nygaard initiated a project for a simulation language at the Norwegian Computing Center, based on his previous use of the Monte Carlo simulation and his work to conceptualise real - world systems . Ole - Johan Dahl formally joined the project and the Simula programming language was designed to run on the Universal Automatic Computer (UNIVAC) 1107 . In the early stages Simula was supposed to be a procedure package for the programming language ALGOL 60 . Dissatisfied with the restrictions imposed by ALGOL the researchers decided to develop Simula into a fully - fledged programming language, which used the UNIVAC ALGOL 60 compiler . Simula launched in 1964, and was promoted by Dahl and Nygaard throughout 1965 and 1966, leading to increasing use of the programming language in Sweden, Germany and the Soviet Union . In 1968 the language became widely available through the Burroughs B5500 computers, and was later also implemented on the URAL - 16 computer . In 1966 Dahl and Nygaard wrote a Simula compiler . They became preoccupied with putting into practice Tony Hoare's record class concept, which had been implemented in the free - form, English - like general - purpose simulation language SIMSCRIPT . They settled for a generalised process concept with record class properties, and a second layer of prefixes . Through prefixing a process could reference its predecessor and have additional properties . Simula thus introduced the class and subclass hierarchy, and the possibility of generating objects from these classes . The Simula 1 compiler and a new version of the programming language, Simula 67, was introduced to the wider world through the research paper "Class and Subclass Declarations" at a 1967 conference . </P>

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