Fence after Fence

Alan Kay's Turing Award Lecture ends with a demo that shows the drive-a-car thing – a fascinating exploration of object oriented programming, a fulfillment of his expression that "everything is an object."

Meta abstraction

He talks about classes as being horizontal, not hierarchical, all independent of each other – an aspiration perhaps not fully achieved in Smalltalk. There, classes were nested like Russian dolls.

One of his most interesting comments was that "meta is safe if you allow fence after fence after fence." Here he means meta as a higher abstraction.

His idea of a fence is closely aligned with Alexander's concept of boundaries that is found in his 15 Properties:

>**Property 3: Boundaries** In nature, we see many systems with powerful, thick boundaries. The thick boundaries evolve as a result of the need for functional separations and transitions between different systems. They occur essentially because wherever two very different phenomena interact, there is also a ‘zone of interaction’ which is a thing in itself, as important as the things which it separates.

15 Properties

Boundaries are one of the three properties of "wholeness" for each element in his Natural Order – his description of the essential characteristics defining vital, autopoietic systems:

* Strong Center (intention) * Boundaries (responsibility) * The Void (white space - ma)