295: Highlights

Programs should obey the explicit-representation principle: classes should reflect natural categories.
Programs should obey the modularity principle: program elements should be divided into coherent classes.
Programs should obey the no-duplication principle: variables and methods should be situated among class definitions to facilitate sharing.
Programs should obey the look-it-up principle: class definitions should include instance variables for frequently requested information.
If you find yourself using the phrase an X is a Y when describing the relation between two classes X and Y, then the first class is a subclass of the second.
If you find yourself using X has a Y when describing the relation between two classes, X and Y, then instances of the second class appear as parts of instances of the first class.