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Discussion 4 - Elspeth Watson

History of Object Systems from Midterm Review Sp2000.


What is Sketchpad?

Was made by Ivan Sutherland at MIT in 1963. It is basically a graphics editor of today's standards. The ideas in Sketchpad were the start of inheritance. One could have a master drawing which you could have other drawings inherit from. So if you change the master drawing all the ones inheriting from it would also change. Sketchpad was amazingly fast (even by today's standards) and the virtual canvas was about third of a mile square.

What is Simula?

This is a program language tha twas meant to make simulations easier to implement. It was made in Norway in the early 1960s. You can esentially make objects (it was not called that then). You could creat many processes (objects) which was a instance of an activity. A simulation had its own class in which the data and behavior could not be changed without permission. This is basically encapsulation - where each object has its own data and behaviors and any other object cannot change those behaviors and data with out the objects permission. Lots of objects can act independently and at the same time. In a simulation it is important to have this act at the same time or appear to act a the same time.

What do they have to do with C++?

Both Sketchpad and Simula had a huge influence on the birth of object-oriented program. Alan Kay at the University of Utah was looking at both Simula and Sketchpad. He relized how they were related and found out that this is the key to having large, complex systems. Since Kay was a Biology major he had everything based on the real world. This is the beginning of Object-oriented design. C++ is an object-oriented language and that is how it is related.

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