AppleScript: The Definitive Guide

The Open Scripting Architecture

In 1992-93, the founders of AppleScript had to decide where the language should live. They could have made AppleScript the internal language of a single application, like HyperCard’s HyperTalk; the user would then compile and run AppleScript code entirely from within this one application. But this approach was unacceptable. Rather, they wanted AppleScript to be available everywhere. Thus the language would have to be part of the System. In creating a place within the System to put it, they generalized this place to be somewhere that not only AppleScript but any scripting language could live in. The resulting structure is the Open Scripting Architecture (OSA).

Components

Under the OSA, a scripting language is implemented by a something called a component. (Components were not invented specially for the OSA; they existed already in connection with QuickTime.) Think of a component as a piece of self-contained functionality made available at system level so that any program can hook up to it and use it. One thing that’s special about components is that they can be installed and uninstalled dynamically. So an OSA-savvy program doesn’t necessarily think in terms of any particular scripting language; it asks the System—in particular, the Component Manager—what scripting languages are presently installed, and if it wants to use one, the Component Manager provides access to it.

Since components are installed dynamically, this installation must actually take ...