OSA

The Open Scripting Architecture, which has been present on the Mac since the early 1990s, is Apple Computer’s mechanism for making interapplication communication available to a spectrum of scripting languages. AppleScript is the OSA language that Apple provides, but there are other OSA-compliant languages, including UserLand Frontier and JavaScript.[2]

OSA accomplishes this “the-more-the-merrier” approach to scripting systems by using Apple events as the unifying technology. The situation is similar to Open Database Connectivity (ODBC) on the Windows platform, where any client application can talk to different database management systems using ODBC as a common conduit (as long as ODBC driver software exists for that particular database). In terms of OSA, the conduit (on Mac OS 9) is a scripting component that can convert whatever scripting language is used (AppleScript or JavaScript) into one or more properly constructed Apple events. Figure 1-3 shows the same Apple event being sent to an application in two different scripting languages.

OSA scripting tools send Apple events
Figure 1-3. OSA scripting tools send Apple events

Before AppleScripts or other scripting languages can be compiled and run, their corresponding extension files have to be installed (the AppleScript extension is included in an OS 9 installation) and then loaded into the computer’s memory. The AppleScript extension or component is depicted in Figure 1-3.