Every SCI game uses a standard library of predefined classes. This concept is very similar to the JDK used by the Java language. This set of standard SCI classes was continually added to as time went on and new games were released. The table below is an attempt to identify what classes were available from the beginning and what classes were added later on and at what point these classes were added.
It is also clear from various clues that the compiled name of some classes is not the same as the original name as used in the source code. For example, in the QFG2 debug mode it is possible to activate a feature called "Feature Writer". This feature is able to generate some simple SCI source code for instances of the following SCI classes: Actor, PicView, Prop, View and Feature. In the compiled version of these classes, the names are instead Act, PV, Prop, View and Feature (notice the difference in the case of the first two). The Official Book of King's Quest also refers to the Actor class rather than Act. It is therefore likely that the source code for a class was able to define a shorter name for inclusion in the compiled script file. The following table, in addition to being a list of the standard set of SCI classes, is also an attempt to identify what the original names were for the cases where the compiled class name is clearly an abbreviation or truncation.
Note: VOCAB.996 contains the "class table". It is described in the SCI Specifications. This is a good starting point for determining where the classes are in each game.