The finite state machine approach

Any input item entering the machine has the effect of producing 

a number (possibly zero) of output items depending on the input item and the state of the machine prior to interpreting the input item. 

The semantics of an input item is defined as the effect which it will produce when received by the finite state machine. 

the pre-processor which converts CAD data base contents into a neutral file, 

the post-processor which converts neutral files into CAD data base content, 

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