hello cyboman,
think of , say, 4to1 multiplexer.
you can write the code in verilog or vhdl for the mux.
there are thre ways describing the mux in hdl.
imagine the blackbox model with input and outputs of mux alone.
-if you write the code as the mux consisting of 'gates' ,
then it is 'structural' model.
-if you write the 'boolean equation' or 'truth table ' of mux
then it is 'rtl' model .
-on the other hand , without worrying the above two ,
you can write it as, something like,
if(selects0,s1==00)
o/p=a;
....
this model is 'behaviour'
in 'behaviuoral model u dont worry about what is the logic
or boolean equationof the mux.. just input/output relationship.
write its 'behaviour' ,in a highlevel construct of 'if...' etc.
hope u get.
srizbf
30thapril2010