There are five very useful VOCAB files that come with all SCI0 games.
VOCAB.000: Contains the words that may be used in the game.
VOCAB.996: Contains the class table that says what SCRIPT files each class number is in.
VOCAB.997: Contains the list of selectors that apply to the current game.
VOCAB.998: Contains the list of SCI byte codes.
VOCAB.999: Contains the list of Kernel functions.
These five VOCAB files will be particularly useful when creating the decompiler.